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Light-dependent photosynthetic characteristics indicated by chlorophyll fluorescence in five mangrove species native to Pohnpei Island, Micronesia
Abstract
To investigate the adaptive capacity to strong light among mangrove species, we examined light-dependent properties of photosynthesis in relation to photoinhibition using chlorophyll fluorescence for sun-leaves of five mangrove tree species; Sonneratia alba, Rhizophora stylosa, Rhizophora apiculata, Bruguiera gymnorrhiza and Xylocarpus granatum. These species were classified into three groups; pioneer -S. alba and R. stylosa, intermediate -R. apiculata and B. gymnorrhiza and climax species -X. granatum. A further distinction can be made between the two intermediate species, the less shade-tolerant R. apiculata and the shade-tolerant B. gymnorrhiza. There was a clear association between successional status and light-saturated electron transport rate (ETR) where ETR was higher in S. alba and R. stylosa > R. apiculata and B. gymnorrhiza > X. granatum. Based on its lower initial slope of light-dependent ETR and lower ratio of variable to maximum fluorescence (Fv/Fm) after a dark-adaptation, X. granatum appeared to suffer greater photoinhibition than other species. The response of qP, which represents PSII openness, to incident light indicates a ranking of tolerant capacity to photoinhibition of S. alba and R. stylosa > R. apiculata > B. gymnorrhiza and X. granatum. The difference in qP response between R. apiculata and B. gymnorrhiza might be attributed to the higher leaf absorptance and the lower degree of thermal dissipation indicated by the higher F'v/F'm in B. gymnorrhiza. It appears that the co-ordination of leaf absorptance, thermal dissipation and consumption of absorbed light energy through electron transport is important in the acclimation of mangrove species to exposed habitats.
... Light availability is a significant factor in the establishment of seedlings and further species composition (Denslow, 1987). Even though, the quantitative information on the light adaptability of seedlings in various parts of the tropical forests are available (Chazdon and Fetcher, 1984b;Smith et al., 1992;Clark et al., 1996;Kitao et al., 2003;Gyimah and Nakao, 2007;Liu et al., 2007), such information for the tree species of the Western Ghats is lacking. ...
... The above studies are based on gas exchange measurements using portable photosynthetic system. Now a days, in addition to gas exchange method, the measurement of chlorophyll a fluorescence has been widely used as a useful technique for obtaining rapid quantitative and qualitative information about the performance of photosynthetic system compared to gas exchange measurements (Goedheer, 1972;Krause and Weis, 1991;Schreiber et al., 1995;Kitao et al., 2003;Govindjee, 2004;Sreejith et al., 2004;Kitao et al., 2006;Govindjee et al., 2007). ...
... Even though several experimental data on photosynthetic performance and successional status of tree species in different parts of tropical region are available (Hozumi, et al., 1969;Bjorkman,, 1981;Bazzaz and Carlson, 1982;Langenheim et al., 1984;Ramos and Grace, 1990;Riddoch et al., 1991;Kitao et al., 2003;Slik, 2005;Gyimah and Nakao, 2007), such data for the indigenous trees of Western Ghats of India are limited. Available literature indicates that, in this part of the tropical forests, some studies have been conducted to understand the ecophysiology and photosynthetic performance of many economically important plants (Lee and Patel, 1987). ...
... Avoidance of light-absorption through lower chlorophyll contents plays an important protective role at the leaf level (Havaux and Tardy 1999). Consumption of absorbed light energy both by thermal dissipation in the chlorophyll antenna system and by energy dissipation via electron transport are also relevant to the mitigation of photoinhibition in sun-exposed habitats (Demmig-Adams et al. 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003b. In earlier studies, energy dissipation through electron transport was observed to be of more significance than thermal energy dissipation to influence the susceptibility of photoinhibition among mangrove species (Kitao et al. 2003b), and among mountain birch seedlings raised under different water regimes (Kitao et al. 2003a). ...
... Consumption of absorbed light energy both by thermal dissipation in the chlorophyll antenna system and by energy dissipation via electron transport are also relevant to the mitigation of photoinhibition in sun-exposed habitats (Demmig-Adams et al. 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003b. In earlier studies, energy dissipation through electron transport was observed to be of more significance than thermal energy dissipation to influence the susceptibility of photoinhibition among mangrove species (Kitao et al. 2003b), and among mountain birch seedlings raised under different water regimes (Kitao et al. 2003a). ...
... As well as leaf N content, stomatal conductance can influence ETR via changes in intercellular CO 2 concentration. ETR would decrease with C i decreasing under saturating light intensities where the ratio of photosynthesis/photorespiration decreases (Farquhar et al. 1980, Kitao et al. 2003b). ...
... Avoidance of light-absorption through lower chlorophyll contents plays an important protective role at the leaf level (Havaux and Tardy 1999). Consumption of absorbed light energy both by thermal dissipation in the chlorophyll antenna system and by energy dissipation via electron transport are also relevant to the mitigation of photoinhibition in sun-exposed habitats (Demmig-Adams et al. 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003b. In earlier studies, energy dissipation through electron transport was observed to be of more significance than thermal energy dissipation to influence the susceptibility of photoinhibition among mangrove species (Kitao et al. 2003b), and among mountain birch seedlings raised under different water regimes (Kitao et al. 2003a). ...
... Consumption of absorbed light energy both by thermal dissipation in the chlorophyll antenna system and by energy dissipation via electron transport are also relevant to the mitigation of photoinhibition in sun-exposed habitats (Demmig-Adams et al. 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003b. In earlier studies, energy dissipation through electron transport was observed to be of more significance than thermal energy dissipation to influence the susceptibility of photoinhibition among mangrove species (Kitao et al. 2003b), and among mountain birch seedlings raised under different water regimes (Kitao et al. 2003a). ...
... As well as leaf N content, stomatal conductance can influence ETR via changes in intercellular CO 2 concentration. ETR would decrease with C i decreasing under saturating light intensities where the ratio of photosynthesis/photorespiration decreases (Farquhar et al. 1980, Kitao et al. 2003b). ...
To investigate the adaptive capacity to strong light, we examined photosynthetic properties in relation to photoinhibition for sun-leaves of 6 tropical fruit tree species native to Malaysia. The 6 species are: Bouea macrophylla (Bm), Callerya atropurpurea (Ca), Canarium sp. (Csp), Cynometra cauliflora (Cc), Morinda citrifolia (Mc) and Syzysuim oleyana (So). They are edible for endemic animals and birds. The degree of chronic photoinhibition indicated by a decrease in pre-dawn F v /F m was well associated with an accumulation of excessive excitation energy in PSII indicated by the decrease in photochemical quenching (qP). Among species, Ca and Mc showed lower degrees of photoinhibition with higher qP. As higher electron transport rate (ETR) was observed with higher qP whereas there was no significant relationship between thermal dissipation (indicated by a decrease in F v ´/F m ´) and qP. Energy dissipation via electron transport was suggested to be more important to keep qP high and to prevent photoinhibition. Higher ETR in Ca appears to result from the higher area-based leaf N while that in Mc might be achieved by the higher stomatal conductance.
... Moreover, shade leaves are more vulnerable to photoinhibition than sun leaves. Energy dissipation through the electron transport system, together with thermal energy dissipation in PSII antennae, constitute an effective way to prevent photoinhibition (Ögren 1991, Demmig-Adams et al. 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003a, 2003b). A greater capacity for electron transport could be expected in thicker leaves with higher LMA, which is associated with higher N area (Pearcy and Sims 1994, Evans 1996). ...
... Evans 1989 Evans , 1996). The morphological differences between the species studied suggest that they differ in electron transport capacity and hence the ability to cope with sudden exposure to high irradiances (Ögren 1991, Park et al. 1996, Baroli and Melis 1998, Niyogi 1999, Kitao et al. 2003a, 2003b ). We observed higher ETR in shaded Q. mongolica than in shaded A. mono, especially in deep shade (Figure 3). ...
... However, Q. mongolica and A. mono grown in moderate shade showed little difference in susceptibility to photoinhibition and chronic photoinhibition (Figure 4 andTable 2). Thermal energy dissipation as well as electron transport are important in preventing photoinhibition by keeping PSII reaction centers open, i.e., by maintaining high q P (Ögren 1991, Park et al. 1996, Baroli and Melis 1998, Niyogi 1999, Kitao et al. 2003a, 2003b ). Non-photochemical quenching is proportional to thermal energy dissipation in PSII antennae (Björkman and Demmig-Adams 1994). ...
We investigated susceptibility to photoinhibition in leaves acclimated to different light regimes in intermediately shade-tolerant Japanese oak (Quercus mongolica Fisch. ex Turcz. var. crispula (Blume) Ohashi) and shade-tolerant Japanese maple (Acer mono Maxim. var. glabrum (Lév. et Van't.) Hara), to elucidate adaptability to gap formation in leaves differing in shade acclimation. We hypothesized that there is a tradeoff between shade adaptation and capacity to mitigate photoinhibition associated with leaf morphology. We simultaneously measured chlorophyll fluorescence and gas exchange in seedlings that had been grown in full sunlight (open), 10% of full sun (moderate shade) and 5% of full sun (deep shade). Shade-tolerant A. mono adapted to deep shade through changes in leaf morphology, lowering its leaf mass per area (LMA), but Q. mongolica showed little change in LMA between moderate and deep shade. Photochemical quenching (qP) did not differ between species in full sunlight and moderate shade; however, in deep shade, qP of Q. mongolica was higher than that of A. mono, suggesting that Q. mongolica grown in deep shade is less susceptible to photoinhibition at gap formation. This is consistent with the finding that chronic photoinhibition 3 days after the transfer to full sunlight, indicated by the decrease in maximum photochemical efficiency, Fv/Fm, at predawn, was less in deep-shade-grown Q. mongolica than in deep shade-grown A. mono. In deep shade, the electron transport rate (ETR) of Q. mongolica was higher than that of A. mono, whereas thermal energy dissipation through photosystem II antennae, indicated by non-photochemical quenching, was lower in Q. mongolica than in A. mono. In deep shade, the greater ETR capacity in Q. mongolica in association with higher LMA and higher leaf N content could contribute to maintaining high qP and mitigating photoinhibition. These results indicate that, by maintaining a high electron transport capacity even in deep shade, the gap-dependent and intermediate-shade-tolerant Q. mongolica trades improved shade adaptation for higher growth potential when a gap event occurs.
... Seven transects were situated in the coral reef type habitat and two were in the estuary type habitat (Figure 1). Four transects were along a line of permanent plots established in 1994, 2002and 2003(Fujimoto et al., 1995bTabuchi, 2006). Transects a to e, h and I, which were examined between 1988 and 1993, have been described in our previous publications (Fujimoto et al., 1995a(Fujimoto et al., , 1995bMiyagi & Fujimoto, 1989;Miyagi et al., 1995). ...
... We established permanent plots in Pohnpei mangrove forests and have monitored forest dynamics since 1994 in order to ascertain the successional characteristics of these forests (Fujimoto et al., 1995b(Fujimoto et al., , 2013Tabuchi, 2006). On the other hand, Kitao et al. (2003) found that the light-saturated electron transport rate was higher in S. alba and R. stylosa > R. apiculata and B. gymnorrhiza > X. granatum. Additionally, the tolerant capacity for photo-inhibition was higher in S. alba and R. stylosa > R. apiculata > B. gymnorrhiza and X. granatum. ...
... Short leaf longevity (i.e. a high turnover rate of leaves) is often associated with a higher relative growth rate and a higher photosynthetic assimilation rate (Reich et al. 1991). Kitao et al. (2003) reported that the light-saturated electron transport rate, which can be correlated with the photosynthetic rate, was highest in Sonneratia alba, followed by Rhizophora apiculata and Bruguiera gymnorhiza, and was lowest in Xylocarpus granatum (Avicennia alba was not measured). The result from the present study that leaf longevity is negatively correlated with RHGR in gaps implies that leaf-level traits (leaf turnover and photosynthesis) correspond directly to the individual-level growth rate in mangrove saplings. ...
... Thus, X. granatum saplings could have a small crown with a low extension cost, contributing to growth under a closed canopy. In addition, shade saplings of X. granatum surprisingly increased total leaf area to the same extent that sun saplings did (Fig. 4b), probably because of a negative influence of high light on sun leaves due to less effective protective mechanisms against photoinhibition (Kitao et al. 2003). ...
We investigated the regeneration pattern of mangrove forests, considering the correspondence between growth strategies (i.e. sapling growth, crown architecture, leaf dynamics) of 5 canopy-dominant species and the disturbance regime in Ranong, Thailand. Individual canopy gap size and percent gap area were greater in the Sonneratia alba-Avicennia alba (SA) zone, which is located on the most seaward fringe, than in the other inland zones. In canopy gaps, the seaward species S. alba and A. alba showed a higher relative height growth rate than the inland species Rhizophora apiculata, Bruguiera gymnorhiza and Xylocarpus granatum. Under closed canopies, the seaward species showed greater mortality, presumably due to their low shade tolerance, while the inland species demonstrated a net growth in spite of the dark conditions. Leaf longevity of sunlit saplings increased from seaward to inland species. The 2 seaward species had well-branched, slender and deeper crowns, while R. apiculata and B. gymnorhiza had wider and flatter crowns, and X. granatum had less-branched, smaller crowns. Phenotypic traits were correlated with each species' growth strategy (potential growth rate and shade tolerance), which corresponded to the disturbance regime in each vegetation zone. Many large gaps may enhance the abundance of S. alba and A. alba in the SA zone, and a few small gaps may prevent establishment and growth of light-demanding species in the inland zones. Accordingly, the correspondence of disturbance regime and growth strategies of canopy-dominant species provides an advantage for successful regeneration, and may contribute to the maintenance of the present species composition in each vegetation zone.
... Disturbance regime matched with regeneration strategies of canopy dominant species in each zone. Because S. alba and A. alba need high light conditions for their growth (Lee et al. 1996;Panapitukkul et al. 1998;Kitao et al. 2003), their seedling and sapling densities were greater in gaps than in the understorey. Formation of many large gaps may facilitate establishment and growth for S. alba and A. alba in SA zone. ...
... Formation of many large gaps may facilitate establishment and growth for S. alba and A. alba in SA zone. On the contrary, the other canopy dominants (R. apiculata, B. gymnorrhiza, and Xylocarpus spp.) can tolerate less light than S. alba and A. alba (Putz and Chan 1986;Tamai and Iampa 1988;Robertson et al. 1990;Clarke et al. 2001;Allen et al. 2003;Kitao et al. 2003;Krauss and Allen 2003) and they showed greater seedling and sapling densities under closed canopy than gaps in each forest. These species may not need large gaps for their establishment and growth (Clarke 2004). ...
Tropical mangrove forests are characterized by clear zonation along a tidal gradient, and it has been supposed that the zonation is primarily controlled by soil factors. However, effects of disturbance on mangrove forests are still not well understood and may play an important role on the vegetation patterns and forest dynamics in some forest formations. In this study, the pattern of disturbance regime and its effects on regeneration of tropical mangrove forests along a tidal gradient were investigated in Ranong, Thailand. We established one or two 0.5ha plots in four vegetation zones, i.e. Sonneratia alba–Avicennia alba zone, Rhizophora apiculata zone, Ra – Bruguiera gymnorrhiza zone, Ceriops tagal–Xylocarpus spp. zone. Gap size (percentage gap area to total study area and individual gap size) was the largest in Sa–Aa zone which is located on the most seaward fringe, and it declined from seaward to inland. Canopy trees of S. alba and A. alba had stunted trunks and showed low tree density. On the contrary, canopy dominants in the other three inland zones, e.g. R. apiculata, B. gymnorrhiza, and Xylocarpus spp., had slender trunks and showed high tree density. Accordingly, differences in disturbance regime among the four zones were resulted from the forest structural features of each zone. Disturbance regime matched with regeneration strategies of canopy dominants. Seedlings and saplings of S. alba and A. alba, which need sunny condition for their growth, were abundant in gaps than in understorey. By contrast, R. apiculata, B. gymnorrhiza, and Xylocarpus spp., which can tolerate less light than S. alba and A. alba, had greater seedling and sapling density under closed canopy than gaps. Many large gaps may enhance the abundance of S. alba and A. alba in Sa–Aa zone, and a few small gaps may prevent the light demanding species to establish and grow in the other inland zones. Correspondence of disturbance regime and regeneration strategies (e.g. light requirement) of canopy dominants may contribute to the maintenance of the present species composition in each of the vegetation zones.
... As Rubisco is closely correlated to total leaf N (Evans 1989), the electron flow capacity would also change via leaf N area variation along the intra-canopy light gradients. In many cases, thermal energy dissipation appears to play the role of compensating less electron flow capacity, i.e. a higher electron flow is accompanied with less thermal energy dissipation as indicated by the lower non-photochemical quenching (NPQ), whereas a lower electron flow is compensated by a higher NPQ (Kitao et al. 2000, 2003b, Rosenqvist 2001, Einhorn et al. 2004). There would be two possibilities for photosynthetic acclimation in leaves grown within a canopy to circumvent photoinhibition: (1) the electron flow capacity is adjusted to optimally utilize the predominant average light and thermal energy dissipation is additionally invoked in the case of sunflecks or (2) the electron flow capacity is adjusted to utilize the peak light (i.e. ...
... A decrease in F v /F m indicates an increase in thermal energy dissipation in PSII antennae (Demmig-Adams et al. 1996, Verhoeven et al. 1998. Lower F v /F m was observed in leaves grown under higher irradiance (Fig. 9B), suggesting a higher capacity of thermal energy dissipation in sun-grown leaves at the peak PPFD (Verhoeven et al. 1998, Kitao et al. 2003b. Although the fraction of excess energy ((1-q P )F v /F m ) at PPFD max was higher in the shade leaves because of lower q P and higher F v /F m (Fig. 9), the rate of excess energy production had no significant trend across Q int range because PPFD max was relatively lower for shade-grown leaves. ...
We investigated the morphological and physiological acclimation of leaves grown within a canopy of Japanese oak tree (Quercus mongolica var. crispula) in terms of the susceptibility to photoinhibition under various growth light conditions. The maximum rates of photosynthesis (P(max) ) and electron transport (ETR(max) ) were higher in mature leaves grown under stronger light with higher area-based leaf nitrogen (N) content closely associated with higher leaf mass per area. The net photosynthetic (P(n) ) and electron transport (ETR) rates corresponding to the daily peak photosynthetic photon flux density (PPFD(max) ) during leaf maturation were almost comparable to P(max) and ETR(max) , respectively. Conversely, P(n) and ETR at the daily average PPFD (PPFD(avg) ) were substantially low in shade-grown leaves when compared with P(max) and ETR(max) . The susceptibility to photoinhibition at PPFD(max) , i.e. at sunflecks for the shade-grown leaves, was assessed by the rate of excess energy production. Although sun leaves showed higher rates of electron transport and thermal energy dissipation than shade leaves under PPFD(max) conditions, the rate of excess energy production was almost constant across shade to sun leaves. The shade leaves of the Japanese oak grown within a crown were suggested to adjust their N investment to maintain higher photosynthetic capacities compared with those required to maximize the net carbon gain, which may facilitate the dissipation of the excessive light energy of sunflecks to circumvent photoinhibition in cooperation with thermal energy dissipation.
... Although drought stress might alleviate the susceptibility to photoinhibition in leaves grown in elevated [CO 2 ], studies on field-grown plants subjected to both elevated [CO 2 ] and drought have shown either an increase (Scarascia -Mugnozza et al. 1996) or a decrease in photoinhibition (Jones et al. 1995). Because variations in the operating intercellular [CO 2 ] (C i ) and carboxylation capacity of Rubisco can influence the rate of electron flow (Harley et al. 1992, Kitao et al. 2003a, which is an effective pathway of energy dissipation to mitigate photoinhibition (Demmig-Adams et al. 1996, Evans 1996, Park et al. 1996, Baroli and Melis 1998, Kitao et al. 2003b, Einhorn et al. 2004, the variable results obtained could be explained by leaf measurements made at the different C i values that occur in the dry and wet seasons, and by modifications in carboxylation capacity of Rubisco. ...
... Thermal energy dissipation and electron transport are important factors in preventing photoinhibition by keeping PSII (Ögren 1991, Park et al. 1996, Baroli and Melis 1998, Niyogi 1999, Kitao et al. 2003a, 2003b. Because NPQ is proportional to thermal energy dissipation (Björkman and Demmig-Adams 1994), the increases in thermal energy dissipation observed with decreasing C i in seedlings in all of the water availability and CO 2 treatment combinations ( Figure 3D) might contribute to preventing photoinhibition as stomata began to close (Kitao et al. 2003a). ...
The interaction of drought and elevated carbon dioxide concentration ([CO(2)]) on carboxylation capacity of Rubisco (V(cmax)) and susceptibility to photoinhibition may be an important determinant of plant responses to seasonal fluctuations in precipitation in an anticipated elevated [CO(2)] environment. Japanese white birch (Betula platyphylla var. japonica) leaves that developed wholly during a period of drought showed an increase in leaf nitrogen and a decrease in leaf carbohydrates that could ameliorate photosynthetic down-regulation, defined as a decrease in V(cmax) in response to elevated [CO(2)]. Photochemical quenching (q(P)) was decreased by elevated [CO(2)] but increased by drought when compared at a given intercellular [CO(2)] (C(i)), indicating that elevated [CO(2)] could increase the risk of photoinhibition, whereas long-term drought could alleviate the risk of photoinhibition. However, only a small variation in q(P) was measured among seedlings in the various water availability x [CO(2)] treatment combinations, consistent with the small treatment differences in chronic photoinhibition among the seedlings, as indicated by the ratio of variable to maximum chlorophyll fluorescence after overnight dark-adaptation. Our results suggest that the offsetting responses-reduced V(cmax) plus increased C(i) at elevated [CO(2)] and increased V(cmax) plus reduced C(i) under drought conditions-resulted in a narrow range of susceptibility to photoinhibition at the growth [CO(2)] in Japanese white birch seedlings grown in various water availability x [CO(2)] treatment combinations.
... Mangroves are physiologically interesting plants thriving in a harsh environment where conditions are expected to reduce their photosynthetic capacity through photoinhibition. In the natural habitat, mangroves receive high luminosity which is much more than the saturation point of photosynthesis, indicating that mangrove leaves often receive a large amount of excess light energy and may be prone to photo-inhibition (Cheeseman et al. 1994;Kitao et al. 2003;Attiwill and Clough 2018). Mangrove photosynthesis can reach light saturation under the incident photosynthetic photon flux density of 40% sunlight (800-1000 µmol photon.m ...
Kaullysing D, Jogee SY, Mundil SP, Soondur M, Gopeechund A, Ricot M, Jeetun S, Chinta T, Chockalingum J, Mungur D, Kowal B, Kristnama L, Gunness V, Balgobin A, Fakun ZR, Munbodhe V, Nohur MB, Ramdhun D, Ramsurrun LK, Rase S, Seetohul TK, Mattan-Moorgawa S, Ramah S, Bhagooli R. 2023. Variations in photo-physiological responses of shaded and non-shaded mangrove, Rhizophora mucronata tree parts from Mauritius Island, western Indian Ocean. Indo Pac J Ocean Life 7: 71-78. This study assessed and compared the photo-physiological responses of the tree parts of juvenile and adult mangrove, Rhizophora mucronata, under shaded and non-shaded conditions in the northern coast of Mauritius Island. Chlorophyll a fluorescence of mature (dark) leaves, young and mature propagules, lichen, buds, and sepal of adult R. mucronata trees, and of mature and young (pale) leaves of juveniles under natural shaded and non-shaded conditions was measured using a field-portable Diving Pulse-Amplitude-Modulated (D-PAM) fluorometer. Commonly used chlorophyll fluorescence parameters such as Fv/Fm, rETRmax, NPQmax were calculated. The tree parts of adult and juvenile R. mucronata showed considerable variations in their photosynthetic responses. Fv/Fm of adult tree leaves was 30% higher in shaded condition as compared to non-shaded condition. The combined effect of mangrove tree parts and conditions (shaded; non-shaded) resulted in significant differences in mean values of Fv/Fm (three-way ANOVA, p<0.001). Leaves of adult trees had 52% higher rETRmax in shaded condition. While a significant difference (p<0.001) was noted in the mean rETRmax values of various tree parts, the shaded and non-shaded conditions did not have any significant effect on rETRmax (p>0.05). Non-shaded parts of R. mucronata, including the leaves, exhibited higher NPQmax values as compared to shaded conditions. Mean NPQmax varied significantly among mangrove parts (p<0.001), between tree stage (p<0.001) and between conditions (p<0.05). These findings revealed differences in the photosynthetic activities of various mangrove parts of juvenile and adult trees under shaded and non-shaded conditions, a first attempt for the tropical island of Mauritius.
... The sampled trees were young and tree age ranging from 15 to 52 years (Table 1). X. granatum is a shade tolerant tree species (Kitao et al., 2003), and the mean growth rate was (1.63 ± 0.30 mm year -1 ) which is within the range described for X. granatum growing in a Kenyan mangrove ecosystem (Robert et al., 2011). The relatively slow growth rate of this species is also in agreement with other species in the Sundarbans (Chowdhury et al., 2016a;Rahman et al., 2020;Siddique et al., 2021). ...
... Our WUE data corroborates with other results previously reported for R. mangle plants in southern Brazil (Soares et al. 2015). Additionally, other reports have shown a better adaptation of mangrove plants to high salinity under low irradiance (Kitao et al. 2003;López-Hoffman et al. 2006). At least part of this preference for shaded sites may be related to the increase of the WUE, which is an important salt-tolerance factor in mangrove plants (Sobrado 2005), and the decrease of the photodamage of the PSII. ...
Key message
Rhizophora mangle plants tolerate high salinity under field conditions by increasing the transcription of genes involved in photosynthesis, antioxidant system, and salt transport.
Abstract
Rhizophora mangle is a mangrove species adapted to a wide range of salinity and has great ecological importance for mangrove ecosystems. Nevertheless, little is known about the genetic basis underlying the salt-tolerance mechanisms of this species. Here, we investigated the physiological and molecular basis of the salt tolerance in R. mangle under field conditions based on analyses of gas exchange, chlorophyll contents, chlorophyll a fluorescence, and gene expression by qRT-PCR. The gas exchange data showed that the plants growing on both mangrove sites, of low and high salinity, present comparable CO2 assimilation rates and stomatal conductance. Our data suggest that the photosynthetic maintenance under high-salinity conditions was supported by an improved PSII activity, as indicated by chlorophyll a fluorescence parameters and chlorophyll a/b ratio, including the increase of active reaction centers (RCs) and stable oxygen-evolving complexes (OECs). Additionally, the psbA (D1 protein of the RC) and PSBO2 (subunit of the OEC) genes were up-regulated under high salinity, which may be related to increased efficiency to repair injuries in the RC and OEC through the synthesis of new subunits, improving the PSII activity. Likewise, the expression of genes involved in ATP synthesis, RubisCO activation, ROS scavenging, GABA synthesis, and vacuolar Na⁺ sequestration was up-regulated under high salinity. Thereby, the energy balance and the avoidance of oxidative stress and ion toxicity are also important means by which R. mangle deals with increasing salt levels in natural environments. Taken together, our data shed light on the salt-tolerance mechanisms of R. mangle in its natural ecosystem, including the findings of some possible salt-regulated genes.
... The levels of SPAD value and photosynthetic pigment content in leaves reflect not only the photosynthetic capacity, but also the adaptation to the environment [27]. There are many kinds of photosynthetic pigments, among which Chl a, Chl b, and carotenoids are the main pigments for photosynthesis, and their contents directly affect the photosynthetic performance of plants. ...
Paeonia ostii is an emerging woody oil crop, but the high temperature in summer is extremely unfavorable for its growth and development. Understory intercropping cultivation would provide shaded environments which could effectively reduce the ambient temperature. In order to explore whether understory intercropping cultivation would reduce the effects of high-temperature stress on P. ostii, the changes of leaf physiological indicators and leaf microstructures of sole-cropping and intercropping P. ostii were investigated. P. ostii that intercropping cultivated under Illinois pecans (Carya illinoinensis (Wangenh.) K. Koch) with 4 m × 4 m and 4 m × 8 m rowing spaces were used as samples in this study. The results showed that with continuous high temperature, the high-temperature damage index of P. ostii kept increasing, whereas the leaf relative water content continued to decline. Compared to sole-cropping, the high-temperature damage index, relative electrical conductivity, proline content, antioxidant enzymes superoxide dismutase (SOD), and ascorbate peroxidase (APX) activities of intercropping P. ostii under C. illinoinensis were significantly decreased, whereas the leaf relative water content was higher. Moreover, compared to sole-cropping, intercropping P. ostii under C. illinoinensis increased SPAD and chlorophyll contents, made mesophyll cell ultrastructures more intact, and made the chloroplasts rounder and more filled with starch granules and lipid globules, leading to enhanced photosynthesis (Pn) and transpiration rates (Tr). Notably, the reduction of high-temperature damage on intercropping P. ostii under C. illinoinensis with 4 m × 4 m rowing spaces was more significant than that under C. illinoinensis with 4 m × 8 m rowing spaces. This research provides some reference values for efficient plantation of P. ostii in the middle and lower reaches of the Yangtze River in China.
... The difference in the photosynthetic capacity of mangroves is related to salinity, and high-salinity stress affects the quenching mechanism and ability of photo-protection of plants and the distribution of the species [17]. Moreover, in mangrove leaves, ambient light is often above the light saturation point, so mangroves are often under conditions of excess light energy and may exhibit photo-inhibition [45]. Under high illumination, an excess of absorbed energy often leads to photo-inhibition and the reduced efficiency of photosynthesis. ...
Mangrove ecosystems are vulnerable to rising sea levels as the plants are exposed to high salinity and tidal submergence. The ways in which these plants respond to varying salinities, immersion depths, and levels of light irradiation are poorly studied. To understand photosynthesis in response to salinity and submergence in mangroves acclimated to different tidal elevations, two-year-old seedlings of two native mangrove species, Kandelia obovata and Rhizophora stylosa, were treated at different salinity concentrations (0, 10, and 30 part per thousand, ppt) with and without immersion conditions under fifteen photosynthetic photon flux densities (PPFD μmol photon·m−2·s−1). The photosynthetic capacity and the chlorophyll fluorescence (ChlF) parameters of both species were measured. We found that under different PPFDs, electron transport rate (ETR) induction was much faster than photosynthetic rate (Pn) induction, and Pn was restricted by stomatal conductance (Gs). The Pn of the immersed K. obovata plants increased, indicating that this species is immersed-tolerant, whereas the Pn level of the R. stylosa plants is salt-tolerant with no immersion. All of the plants treated with 30 ppt salinity exhibited lower Pn but higher non-photochemical quenching (NPQ) and heat quenching (D) values, followed by increases in the excess energy and photoprotective effects. Since NPQ or D can be easily measured in the field, these values provide a useful ecological monitoring index that may provide a reference for mangrove restoration, habitat creation, and ecological monitoring.
... In mangrove leaves, the light saturation point (LSP) is usually considerably lower than the light they receive. Thus, mangrove leaves often receive excess light energy and may exhibit photoinhibition (Cheeseman 1994, Kitao et al. 2003. However, there are only a few studies on mangrove photoinhibition and photoprotection (Luna et al. 2019, Wang et al. 2020b. ...
Mangrove ecosystems are vulnerable to rising sea levels. When the sea level rises, the plants are exposed to increased salinity and tidal submergence. In Taiwan, the mangrove species Kandelia obovata and Rhizophora stylosa grow in different habitats and at different elevations. To understand the response of photosynthesis to salinity and submergence in mangroves adapted to different tidal elevations, gas exchange and chlorophyll fluorescence parameters were measured in K. obovata and R. stylosa under different salinity (20 and 40‰) and submergence treatments. The period of light induction of photosynthesis for the two mangrove species was >60 min. In the induction process, the increase in photosystem efficiency was faster than the increase in stomatal opening, but CO2 fixation efficiency was restricted by stomatal conductance. The constraint of stomatal opening speed is related to the conservative water-use strategy developed in response to mangrove environments. Submergence increased the photosynthetic rate of K. obovata, but not that of R. stylosa. Although R. stylosa was more salt tolerant than K. obovata, R. stylosa was not submergence tolerant in a high-salinity environment, which may be the reason for the higher intertidal elevations observed for R. stylosa in comparison with K. obovata. The photosynthetic rate and energy-dependent quenching (qE) of the two mangroves presented a negative relationship with photoinhibition, and high-salt treatment simultaneously reduced photosynthetic rate and qE. A decrease in the photosynthetic rate increased excess energy, whereas a decrease in qE decreased photoprotection; both increased photoinhibition. As the degree of photoinhibition can be easily measured in the field, it is a useful ecological monitoring index that provides a suitable reference for mangrove restoration, habitat construction and ecological monitoring.
... The maximum irradiance of mangroves (PAR) is limited to 2000 mmol m À2 s À1 , beyond which excessive light can damage the plant (Ellison and Farnsworth 2001). Although measuring PAR would be important in future studies as an essential factor affecting photosynthetic activity, Kitao et al. (2003) emphasised that the heterogeneity of individual species, environmental patterns and habitat preferences affect photosynthesis in various mangrove species. These parameters can also affect electron transport rates. ...
The aim of this study was to investigate the photosynthetic performance and litter production of planted (PLA) and natural (NAT) mangroves in Trang, southern Thailand. Relative chlorophyll content and other photosynthetic parameters, such as photosynthetic efficiency of Photosystem II (Phi2), yield of non-regulatory energy dissipation (PhiNO), yield of non-photochemical quenching (PhiNPQ) and quenching due to non-photochemical dissipation of absorbed light energy (NPQt), and litter fall production were determined and compared between two mangrove stands. Measurements of photosynthetic parameters were made using PhotosynQ to assess the health of the community structure in both stands. The assumption of this study, namely that there would be no significant difference in any photosynthetic parameter measured between the two stands, was confirmed using t-test with unequal variances confirmed (P > 0.05 for all). Changes occurred quarterly and in sites with different species. In terms of litter production, significant differences were found according to stand (P < 0.001), season (P < 0.05) and site (Sikao, F3,129 = 4.357, P < 0.01; Kantang, F3,190 = 3.243, P < 0.01). PLA stands demonstrated similar photosynthetic characteristics to NAT stands. This study established the effects of land use changes on PLA mangroves (planted in an abandoned shrimp pond). The overall significance of the study is in highlighting the positive outcomes of mangrove restoration, particularly in degraded mangrove stands due to land use change.
Keywords: ecology, mangroves, physiology, primary production, restoration.
... Therefore, we included the environmental factors Tem, CO 2 and Par in our model. In addition, analysis of the photosynthetic mechanism inside the leaves showed that the fluorescence parameters can accurately predict the photosynthetic capacity 26 . During photosynthesis, the qP measures the degree of closure of the reaction center, the ETR measures the rate of electron transfer during photosynthesis, and the PhiPS2 measures the actual initial light energy capture efficiency of the PSII reaction center with partial closure. ...
Due to the imperfect development of the photosynthetic apparatus of the newborn leaves of the canopy, the photosynthesis ability is insufficient, and the photosynthesis intensity is not only related to the external environmental factors, but also significantly related to the internal mechanism characteristics of the leaves. Light suppression and even light destruction are likely to occur when there is too much external light. Therefore, focus on the newborn leaves of the canopy, the accurate construction of photosynthetic rate prediction model based on environmental factor analysis and fluorescence mechanism characteristic analysis has become a key problem to be solved in facility agriculture. According to the above problems, a photosynthetic rate prediction model of newborn leaves in canopy of cucumber was proposed. The multi-factorial experiment was designed to obtain the multi-slice large-sample data of photosynthetic and fluorescence of newborn leaves. The correlation analysis method was used to obtain the main environmental impact factors as model inputs, and core chlorophyll fluorescence parameters was used for auxiliary verification. The best modeling method PSO-BP neural network was used to construct the newborn leaf photosynthetic rate prediction model. The validation results show that the net photosynthetic rate under different environmental factors of cucumber canopy leaves can be accurately predicted. The coefficient of determination between the measured values and the predicted values of photosynthetic rate was 0.9947 and the root mean square error was 0.8787. Meanwhile, combined with the core fluorescence parameters to assist the verification, it was found that the fluorescence parameters can accurately characterize crop photosynthesis. Therefore, this study is of great significance for improving the precision of light environment regulation for new leaf of facility crops.
... On the other hand, López-Hoffman et al. (2006) observed that under lower luminosity, the survival rates of R. mangle seedlings were higher at higher salinity (25 psu). Therefore, the Rhizophora genus can inhabit places with high luminosity (Kitao et al. 2003) as long as the salinity content is moderate. ...
This study evaluated the photosynthetic efficiency in Rhizophora mangle plants in two mangrove forests, the highest salinity (HS) area, and the lower salinity (LS) area. The CO2 assimilation rate (PN), stomatal conductance, leaf transpiration, intrinsic water-use efficiency, and chlorophyll a fluorescence L-band, IP-phase, and performance index were higher in the LS area. The instantaneous water-use efficiency, initial fluorescence, maximum fluorescence, and J-step were higher in the HS area. The plants growing in the HS area exhibited greater efficiency in electron transfer between the oxygen-evolving complex and the acceptor side of the PSII. The plants growing in the LS area exhibited greater efficiency of the reduction of the final acceptors of the PSI, an important strategy to the stress conditions. The results show that a greater variation in salinity in the LS area had the effect on PN and long-term changes in the rainfall regime may alter the vegetation community of mangrove forests.
... The maximal photochemical efficiency of photosystem II (F v /F m ) was measured with a portable fluorometer (PAM-2000, Walz, Effeltrich, Germany) in September 2017. The measurement was conducted after an overnight dark adaptation to evaluate the chronic photoinhibition (Krause et al., 1995;Kitao et al., 2003). F v /F m was calculated with the following parameters and formula: F 0 for the steady state yields, F m for the maximum yields measured under irradiance of approximately 5,000 µmol m −2 s −1 photon flux density for 1 s, and F v /F m = (F m -F 0 )/F m as defined by Schreiber et al. (1986). ...
The effect of elevated ozone (eO3) and soil salinization with alkaline salts in northeastern (NE) China is a serious concern affecting the success of the national replanting project. As planted areas exceed 4 million hectares in China, we must consider future afforestation efforts after thinning and harvesting. Here, we investigated eO3 and salt stress on Dahurian larch (Larix gmelinii var. japonica; DL) and Japanese larch (L. kaempferi; JL) seedlings. The seedlings were exposed to eO3 (~70 nmol mol−1) and ambient ozone (aO3) (~25~40 nmol mol−1) for one growing season in an open top chamber (OTC) system with simulated salinity in NE China (alkaline salt, NaHCO3:NaCl = 9:1, 20mM Na+). The seedlings under salt-free treatment received tap water. Although the effects of eO3 on DL were not significant, eO3 significantly increased total dry mass and total leaf area index of JL. There was no significant reduction in total dry mass under salt stress in both species. The relationship between needle Na and other mineral contents indicated that both species maintained K contents even with excess Na contents in needles. DL showed relatively lower reduction of other mineral contents, indicating higher salt tolerance of needle element homeostasis than JL. Contrary to our hypothesis, there were no interaction effects of eO3 and salt stress on both species. These results indicated that DL seedlings may be more suitable than JL seedlings as a future afforestation species under eO3 levels of <70 nmol mol−1 at saline soil condition.
... This study confirmed the EVI response of mangrove lagged SST of about 1 to 3 months. As mangroves were most strongly related with rainfall seasonality, radiation flux (Ra) was inversely related to EVI seasonality, although there may also have been photo inhibitive effects of high irradiances in mangroves, which are considered "sun plants" with typically very high irradiances point [122][123][124]. ...
Vegetation phenology is the annual cycle timing of vegetation growth. Mangrove phenology is a vital component to assess mangrove viability and includes start of season (SOS), end of season (EOS), peak of season (POS), and length of season (LOS). Potential environmental drivers include air temperature (Ta), surface temperature (Ts), sea surface temperature (SST), rainfall, sea surface salinity (SSS), and radiation flux (Ra). The Enhanced vegetation index (EVI) was calculated from Moderate Resolution Imaging Spectroradiometer (MODIS, MOD13Q1) data over five study sites between 2003 and 2012. Four of the mangrove study sites were located on the Malay Peninsula on the Andaman Sea and one site located on the Gulf of Thailand. The goals of this study were to characterize phenology patterns across equatorial Thailand Indo-Malay mangrove forests, identify climatic and aquatic drivers of mangrove seasonality, and compare mangrove phenologies with surrounding upland tropical forests. Our results show the seasonality of mangrove growth was distinctly different from the surrounding land-based tropical forests. The mangrove growth season was approximately 8–9 months duration, starting in April to June, peaking in August to October and ending in January to February of the following year. The 10-year trend analysis revealed significant delaying trends in SOS, POS, and EOS for the Andaman Sea sites but only for EOS at the Gulf of Thailand site. The cumulative rainfall is likely to be the main factor driving later mangrove phenologies.
... Because of this, agar-based PEG infusion model, introduced in the past decade by van der Weele and co-workers [76], and additionally optimized to mature plants ( Figure 6) seems to be more suited for this purpose. The confirmation of the stress development might rely on the determination of native leaf fluorescence [77], hydrogen peroxide contents [16] and some further parameters. ...
Environmental stress is one of the major factors reducing crop productivity. Due to the oncoming climate changes, the effects of drought and high light on plants play an increasing role in modern agriculture. These changes are accompanied with a progressing contamination of soils with heavy metals. Independent of their nature, environmental alterations result in development of oxidative stress, i.e. increase of reactive oxygen species (ROS) contents, and metabolic adjustment, i.e. accumulation of soluble primary metabolites (amino acids and sugars). However, a simultaneous increase of ROS and sugar concentrations ultimately results in protein glycation, i.e. non-enzymatic interaction of reducing sugars or their degradation products (α-dicarbonyls) with proteins. The eventually resulting advanced glycation end-products (AGEs) are known to be toxic and pro-inflammatory in mammals. Recently, their presence was unambiguously demonstrated in vivo in stressed Arabidopsis thaliana plants. Currently, information on protein targets, modification sites therein, mediators and mechanisms of plant glycation are being intensively studied. In this chapter, we comprehensively review the methodological approaches for plant glycation research and discuss potential mechanisms of AGE formation under stress conditions. On the basis of these patterns and additional in vitro experiments, the pathways and mechanisms of plant glycation can be proposed.
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... The ratio of cut trees to all deceased trees was higher in PC1 than PE1, probably because of a difference in accessibility, namely, PC1 is located in a place which is approached easily from land, while PE1 can only be approached from the sea by boat. The high density of R. apiculata, which is a less shade-tolerant species (Kitao et al., 2003) and usually dominates at relatively lower elevations than B. gymnorrhiza (Mochida et al., 1999), in the landward part of PC1 (Fig. 2) seems to have been caused by severe human impact such as clear cutting. ...
... ), 광합성 능력과 밀접한 관계가 있으며 (Cho et al., 2008), 무차광조건에서 내음성을 지닌 음지성 식물 은 양지성 식물에 비해 광화학반응효율이 낮다고 한다 (Kitao et al., 2003 ...
This study was conducted to investigate the changes of chlorophyll contents, chlorophyll fluorescence, photosynthetic parameters, and leaf growth of Synurus deltoides under different shading treatments. S. deltoides was grown under non-treated (full sunlight) and three different shading conditions (Shaded 88~93%, 65~75%, and 45%~55%). Light compensation point (), dark respiration (), maximum photosynthesis rate (), photo respiration rate (), carboxylation efficiency (), and photochemical efficiency were decreased with increasing shading level; However, compensation point (), total chlorophyll content, and specific leaf area (SLA) were shown the opposite trend. S. deltoides under 88~93% treatment showed the lowest photosynthetic activity such as maximum photosynthetic rate (), photochemical efficiency, and compensation point (). Therefore, photosynthetic activity will be sharply decreased with a long period of 8~12% of full sunlight. With the shading level decreased, carotenoid content and non-photochemical fluorescence quenching (NPQ) increased to prevent excessive light damage. This result suggested that growth and physiology of S. deltoides adapted to high light intensity through regulating its internal mechanism.
... Of course, with the limited number of sites and trees figure 3 is a very rudimentary Table 1. Apparent photosynthetic electron transport rate at an irradiance of 1000 µmol m -2 s -1 (i.e. at or very close to saturation) of five mangrove tree-species in a sun-exposure gradient (after data of Kitao et al. 2003) Species ETR max (µmol m -2 s -1 ) Sun-exposed pioneer species Sonneratia alba Sm. Together with additional information, especially a much higher intrinsic water use efficiency of P. falcatus, the latter observation led to the conclusion that the valuable native tree P. falcatus can well regenerate within the exotic E. saligna-tree plantation, and -appropriate forest management given -even a new Podocarpus-forest may be established (Feyera et al. 2002, Lüttge et al. 2003, Fetene & Beck 2004). ...
In some literature variations in photosynthetic rates are considered to be of little relevance for individual fitness. This depends among other things on how one defines fitness, i.e. if one takes strictly Darwinian fitness as seed production or if one needs to evaluate particular traits and consider plant establishment. It also matters if one takes the Darwinian "organism individual" as the central entity in evolution ("individual fitness") or the "species individual" in a modified "Structure of Evolutionary Theory" sensu Stephen Jay Gould. A phenotypically expressed trait like photosynthetic rate, even if intra- and interspecific differences may be small, can matter in habitat performance and niche acquisition. Light dependence curves (LCs) of photosynthetic rates are now readily measured under field conditions using miniaturized equipment of pulse amplitude modulated fluorometers. In contrast to actual momentary measurements of quantum yield of photosynthesis under actually prevailing ambient conditions, LC measurements reflect the expressed intrinsic capacity of photosynthesis. In this review we explore the power of LC measurements yielding cardinal points such as maximum apparent electron transport rate of photosystem II (ETRmax) and saturating photosynthetically active radiation (PARsat) in making intra- and interspecific comparisons of plant performance and synecological fingerprinting in ecophysiological studies across species, sites, habitats and ecosystems.
... Also, since chronic photoinhibition occurs in a period of restrained growth, associated with a build-up in carbohydrate content (Silva et al. 2004), it is unlikely that photoinhibition per se would largely result in decreased coffee productivity. Furthermore , photoinhibited outer leaves may play a role to attenuate light intensity and so protect inner leaves from photoinhibition (Kitao et al. 2003). Finally, the present results suggest that shading would result in little, if any, additional photoprotection to the peripheral leaves. ...
Coffee is native to shady environments, but often grows and yields better without shade. Thus, it may be reasoned that coffee
leaves should display enough plasticity to acclimate themselves to contrasting light environments. However, little is known
about mechanisms associated with such plasticity in coffee. This work aimed, therefore, to explore differences in leaf photoprotective
mechanisms. Plants were grown in the field and received either 48 or 100% natural light. Evaluations were made using outer
leaves from the sun-facing sides of the coffee hedgerow in Viçosa (Brazil) in August and October, when growth and photosynthetic
rates are expected to be minimal and maximal, respectively, and in December, when temporary depressions in those variables
are common. Regardless of light treatments, coffee leaves showed: (1) very low photosynthetic rates (generally below 2.5μmolm−2s−1), (2) chronic photoinhibition in August (dry, cool season) that was accompanied by strong loss of pigment concentration,
and (3) discrete, dynamic photoinhibition in October and December (rainy, warm season). Compared with shaded leaves, sunlit
leaves generally exhibited lower pigment concentration, lower quantum yield of electron transport, steeper inclinations and
similar electron transport rate. Total ascorbate pool tended to be larger in sunlit than in shaded leaves (but with similar
redox state), whereas activities of key antioxidant enzymes, as well as malondialdehyde accumulation and electrolyte leakage,
were similar between those leaf types. As a whole, the photosynthetic apparatus of the coffee tree showed a low phenotypic
plasticity to varying irradiance.
... for photosynthesis measured in Bruguiera gymnorrhiza at Durban Bay site (Naidoo et al. 2002) is at per (around 1000 mmol m À2 s À1 ) with the present data. In contrast, H. fomes and X. granatum exhibited just an opposite trend that can explain less affinity of these species towards high salinity, irradiance and temperature of the Sundarbans forest. Kiato et al. (2003) placed B. gymnorrhiza as the shade tolerant, intermediately adaptive species to strong light and X. granatum as the climax one. Therefore, co-ordination of leaf absorptance, thermal dissipation and consumption of absorbed light energy through electron transport is important in the acclimation of mangrove species to exposed habitats. Hig ...
Five species of mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa and Xylocarpus granatum) were investigated with respect to their photosynthesis rate, chlorophyll content, mesophyll conductance, specific leaf area,
stomatal conductance and photosynthetic nitrogen use efficiency under saline (15–27PPT) and non-saline (1.8–2PPT) conditions.
Some inorganic elements were estimated from the leaf samples to compare the concentrations with change in salinity. Elevated
assimilation rate coupled with increased chlorophyll content, more mesophyll and stomatal conductance and higher specific
leaf area in non-saline condition indicates that these mangroves can grow well even with minimal salinity in soil. In B.gymnorrhiza, E.agallocha and P.paludosa the optimum PAR acquisition for photosynthesis was higher under salt stress, while the maximal rate of assimilation was lower
even with minimal salinity. H.fomes and X.granatum followed the opposite trend, where the peak photosynthesis rate was lower under non-saline conditions even at a higher irradiance
than in the saline forest. This indicates less affinity of H.fomes and X.granatum to high substrate salinity. Accumulation of Na+ increased in plants in saline substrate, while in most of the species, salinity imposed reduction in Ca+ and Mg+ uptake. Increased K+ content can be attributed to high substrate level K+ in non-saline soil. Trace amount of salinity induced Cu++ detected in leaves of H.fomes may impart some toxic effects. Photosynthetic nitrogen use efficiency increased in non-saline soil that can be attributed
to higher photosynthetic peak in most of the species and/or lower nitrogen accumulation in plant samples.
... e optimum irradiance for photosynthesis measured in Bruguiera gymnorrhiza at Durban Bay site (around 1000 ìmol m -2 s -1 ) (Naidoo et al. 2002). In contrast, H. fomes and X. granatum exhibited just an opposite trend that can explain less affinity of these species towards high salinity, irradiance and temperature prevailing in the Sundarbans forest. Kiato et al. (2003) placed B. gymnorrhiza as the shade tolerant, intermediately adaptive species to strong light and X. granatum as the climax one. High photosynthetic capacity can theoretically increase water use efficiency as more carbon is assimilated per unit water transpired. Though Grassi et al. (2002) and Sefton et al. (2002) denied any relationship ...
Mangroves are physiologically interesting as potential models for stress tolerance and as sources of alternative ideas about
physiological strategies relevant at the ecosystem level. Variation in habitat has great impact on the physiological behavior
and biochemical expression level of a particular plant species. Five species of mangroves, growing in saline and fresh water
conditions were assessed for their ecological fitness in two different habitats. Assessments were based on some physiological
and biochemical parameters measured from the fully exposed mature leaves under saline (15–27 PPT) and non-saline (1.2–2 PPT)
conditions. Among the five species considered for investigation Bruguiera gymnorrhiza, Excoecaria agallocha and Phoenix paludosa grow luxuriously in the Sundarbans forest, while the rest two (Heritiera fomes, Xylocarpus granatum) are scanty. A comparative account of photosynthetic efficiency, chlorophyll content, mesophyll and stomatal conductance,
specific leaf area, photosynthetic nitrogen use efficiency, total foliar free amino acids and differential expression of some
antioxidant isoenzymes in leaf were estimated between the saline and non-saline plants. Elevated assimilation rate coupled
with increased chlorophyll content, increased conductance and higher specific leaf area in non-saline condition indicates
ability of these mangroves to grow even under minimal substrate salinity. The optimum PAR acquisition for photosynthesis in
B. gymnorrhiza, E. agallocha and P. paludosa was higher under salt stress, while the maximum assimilation rate was lower in control plants. The opposite trend occurred
in H. fomes and X. granatum, where the peak photosynthesis was lower under non-saline conditions even at a higher irradiance than in the saline forest.
The isoform patterns of peroxidase, acid phosphatase and esterase indicated considerable difference in regulation of these
enzymes due to salt stress and /or reverse adaptation.
... The latter determines the competition strength of the species. For our simulation this value was set to 0.3 because this describes intermediate species-specific competition strength as documented for R. apiculata by Kitao et al. (2003). The FON scaling parameters a and b are stand-dependent and define the scale of the distance and the strength of competition of neighboring trees. ...
... Physiological acclimation to high irradiance involves reduced nitrogen allocation to light harvesting, increased photoprotective compounds, enhanced dark respiration rate, increased chlorophyll a/b ratio and changes in chloroplast ultrastructure , together leading to high light-saturated CO 2 uptake rates and high light compensation and saturation points (Givnish 1988). The capacity for plastic changes in these traits appears to be inversely linked to shade tolerance of the species (Bazzaz and Carlson 1982, Kitao et al. 2003, Einhorn 2004), although others have reported that the highest physiological plasticity is found in species with intermediate shade tolerance (Murchie and Horton 1997, Naidu and DeLucia 1998). Changes in leaf anatomy constitute a typical component of sun–shade acclimation, with sun leaves possessing a thicker mesophyll, often composed of more cell layers, and having a pronounced palisade layer, more abundant sclerenchymatic tissues and denser stomata than shade leaves (Givnish 1988, Robakowski et al. 2004 ). ...
Leaves developing in different irradiances undergo structural and functional acclimation, although the extent of trait plasticity
is species specific. We tested the hypothesis that irradiance-induced plasticity of photosynthetic and anatomical traits is
lower in highly shade-tolerant species than in moderately shade-tolerant species. Seedlings of two evergreen conifers, shade-tolerant
Abies alba Mill. and moderately shade-tolerant Picea abies Karst., and two deciduous angiosperm species, highly shade-tolerant Fagus sylvatica L. and moderately shade-tolerant Acer pseudoplatanus L., were grown in deep shade (LL, 5% of full irradiance) or in full solar irradiance (HL) during 2003 and 2004. Steady state
responses of quantum yield of PSII (φPSII), apparent electron transport rate (ETR), nonphotochemical quenching (NPQ) and photochemical quenching (qP) were generally
modified by the light environment, with slower declines in φPSII and qP and greater maximal ETR and NPQ values in HL plants in at least one season; however, no link between quantitative
measures of plasticity of these traits and shade tolerance was found. Plasticity of nine anatomical traits (including palisade
cell length, which was reduced in LL) showed no relationship with shade tolerance, but was less in conifers than in deciduous
trees, suggesting that leaf life span may be a significant correlate of plasticity. When LL-acclimated plants were exposed
to HL conditions, the degree and duration of photoinhibition (measured as a decline in maximum quantum yield) was greatest
in F. sylvatica, much lower in P. abies and A. alba, and lowest in A. pseudoplatanus. Thus, as with the other traits studied, vulnerability to photoinhibition showed no relationship with shade tolerance.
In mangrove forests, the hydroperiod is strongly related to tidal dynamics, where the periodic oceanic water movement regulates the level, duration, and frequency of the flooding events. In fringe mangrove forests, Rhizophora mangle propagules deal with variable hydroperiod conditions that sometimes compromise their survival. To disentangle the combined effects of duration and intensity of flooding on physiological and growth variables, we imposed a continuous experiment with three levels of flooding and four flooding durations on seedlings of R. mangle. We collected data at 3 and 6.5 months after exposure to the treatments. Propagule reserves allowed plants to evade the effects of the flood level after a 3-month treatment period. After a 6.5-month exposure, physiology and growth were modulated by the flooding time. Individual plants had higher stem length and lower root and total biomass at prolonged and high flooding levels compared to any other flooding combinations. In both ages, the highest total plant biomass was exhibited in the medium flooding levels and 6 h flooding duration. The plasticity index was higher for morphological and biomass variables than for physiological variables. The high morphological plasticity of R. mangle plants constitutes a competitive advantage to colonize flooded sites in fringed mangrove areas. Our results identify schemes to improve the success of mangrove restoration plans, a critical tool for carbon sequestration and ecosystem service provision.
Based on Chinese ecological policy, we have been studying mangrove ecosystems in southern China, especially from the perspective of pollutants deposition in mangrove wetlands, physiological ecology of mangrove species on the impact of heavy metal pollution and seeking ecosystem restoration. For these, we explored in three aspects: 1) pollutants distribution and ecological risk in main distribution of mangrove, China, 2) eco-statistics and microbial analyses of mangrove ecosystems (including shellfish) in representative locations where mangrove plants are well developed, especially in Shenzhen, a rapid developing economic city in Guangdong Province, 3) ecophysiological experiments on a representative species of mangrove for evaluating combination effects of major nutrient elements and heavy metal pollution on growth and physiological responses of the seedlings. Based on the results, we proposed how to rehabilitate mangrove ecosystem in China under rapidly changing environmental conditions, with a view to our future survival and to provide nature-based solution as well as the public with more ecosystem services.
Chlorophyll a fluorescence is increasingly being used as a rapid, non-invasive, sensitive and convenient indicator of photosynthetic performance in marine autotrophs. This review presents the methodology, applications and limitations of chlorophyll fluorescence in marine studies. The various chlorophyll fluorescence tools such as Pulse-Amplitude-Modulated (PAM) and Fast Repetition Rate (FRR) fluorometry used in marine scientific studies are discussed. Various commonly employed chlorophyll fluorescence parameters are elaborated. The application of chlorophyll fluorescence in measuring natural variations, stress, stress tolerance and acclimation/adaptation to changing environment in primary producers such as microalgae, macroalgae, seagrasses and mangroves, and marine symbiotic invertebrates, namely symbiotic sponges, hard corals and sea anemones, kleptoplastic sea slugs and giant clams is critically assessed. Stressors include environmental, biological, physical and chemical ones. The strengths, limitations and future perspectives of the use of chlorophyll fluorescence technique as an assessment tool in symbiotic marine organisms and seaplants are discussed.
The appearance of the C⁴photosynthetic pathway in the Earth’s flora represents one of the most impressive and curious examples of evolutionary diversification and biogeographic expansion in the history of life (Ehleringer and Monson, 1983). This complex pathway, involving novel patterns of biochemical compartmentation and anatomical design, has evolved with independent but convergent patterns approximately fifty times during the relatively short geological span of 12–15 million years (Kellogg, 1999; Monson, 1999; Sage, 2004; Christin et al., 2007). The appearance of C4photosynthesis has changed the nature of photosynthetic productivity and ecosystem structure on Earth, both regionally and globally. Grassland ecosystems emerged in southwestern Asia, Africa and North America during the mid- to late-Miocene (5–10 Ma) and continued through the Pliocene, (~3Ma), with many of these systems dominated by C4species (Cerling, 1999; Beerling and Osborne, 2006). During the appearance of C⁴ grasslands, the trophic structures of grazed ecosystems were completely revised, resulting in the emergence of novel mammalian lineages (Cerling et al., 1993; Wang et al., 1994; MacFadden and Cerling, 1996; Ehleringer et al., 1997). Arguably, there is not a better example in the history of life to illustrate the tightly integrated nature of evolutionary novelty and ecological impact, as that shown in C⁴ photosynthesis. Clearly, C⁴ photosynthesis, though present in only 8,000 of the estimated 250,000 higher plant species, deserves a significant role in the discussion of plant biology.
This chapter briefly considers the future of stable isotope ecology. The future may hold advances in technology, a more routine use of multiple chemical markers in ecological investigations, and more of that essential scientific ingredient, imagination.
Chlorophyll fluorescence methods have been used to evaluate the effects of environmental stresses on photosynthetic properties. Chlorophyll fluorescence can provide detailed information of photosystem II (PSII) photochemistry, which is vulnerable to environmental stresses such as strong light, low temperature, heat and drought. I reviewed photoinhibition of photosynthesis and discussed the mechanism to prevent photoinhibition in droughtacclimated leaves. As drought stress is often accompanied by strong light, a decline in photosynthesis caused by stomatal closure increases the risk of photoinhibition. Energy dissipation via electron flow would be an effective way to prevent photodamage as well as thermal energy dissipation in PSI1 antennae.
Pteroceltis tatarinowii is considered as an endangered species on the brink of extinction endemic to China. In order to reveal ecophysiology characteristics and gecological adaptability of Pteroceltis tatarinowii in different habitats, the photosynthetic characteristics and chlorophyll fluorescence parameter were studied. The results showed that the light saturation point (336 μmol · m-2 · s -1),light compensate point (10. 93 μmol · m-2 · s-1),maximum net photosynthetic rate (Pn man),and transpiration rate(Tr) of Pteroceltis tatarinowii were higher at the top site than that at foot site, both water utility efficiency(WUE) and water potential were lower at the top site. The fluorescence parameters Fm,Fv,Fv/Fo,Fv/Fm,Fv'/ Fm' at the top site were lower, but photochemistry quench (qP) and PS II electronic transport quantum yield (ΦPS II) of Pteroceltis tatarinowii were higher at foot site under shade condition;under strong light at the top site the qP were lower, ΦPS II were similar as at foot site; and respiration rate of Pteroceltis tatarinowii was lower at the top site. It was obvious that some physiological properties varied with habitat change, Pteroceltis tatarinowii did not seem to be menaced with the strong light and heat drought stress. Consequendy, Pteroceltis tatarinowii at the top site adapted the karst condition well by comprehensive ways such as increasing producing more photosynthetic substance and lowering the respiration et al, while had low shadetolerance at the foot site.
At three simulated acid rainfall intensities with pH values of 2.5 (severe), 4.0 (medium) and 5.6 (light), the responses of chlorophyll fluorescence parameters of Myrica rubra seedlings were studied in three stress ways, i. e. only the aboveground part of seedlings exposed to acid rain (T1), both of the seedlings and soil exposed to acid rain (T2), only the soil exposed to acid rain (T3) compared with blank control (CK). The relative chlorophyll content (SPAD), PS II maximal photochemical efficiency (Fv/Fm), PS II potential activity (Fv/Fo), and PS actual photochemical quantum yield (Yield) under each stress showed T3 >T1 > T2 within six months, and T1 >T3>T2 after six months. It indicated that T2 had the strongest inhibition on seeding. T1 had the stronger inhibition at the early stage while T3 showed the stronger inhibition at the later stage. All chlorophyll fluorescence parameters in the three stress ways were lower than those in the CK group under the severe acid rainfall intensity, while T1 and T3 had higher values than the CK group under the medium and light acid rainfall intensities. It indicated that M. rubra seedlings had strong tolerance ability to acid rain. Acid rainfall at certain intensities could increase the values of chlorophyll fluorescence parameters of M. rubra. The values of Fv/Fm, Fv/ Fo and Yield were higher in summer and autumn than in winter and spring. Significant differences in the values of Fv/Fm and Fv/Fo were found among T1, T2 and T3. © 2015, editorial Board of Chinese Journal of Ecology. All rights reserved.
Since the publication of the first edition of this book ten years ago, international research into the physiological ecology of plants in the tropics has increased enormously in quantity and quality. This brand new edition brings the story right up to date. New approaches have been developed in remote sensing. At the other end of the scale, molecular biology has come on in leaps and bounds, particularly regarding ecological performance of tropical plants, e.g. in understanding the adaptation of resurrection plants to the extreme habitat of inselbergs. In this fully revised and updated second edition the wealth of new information has made it necessary to break large chapters down into smaller ones. Tropical forests which occupy about half of the entire volume of the book are now arranged in five chapters covering structure and function under the influence of environmental cues and including epiphytes and mangroves as part of the tropical forest complex. Savannas are now treated in two chapters. Meanwhile, coastal salinas have been combined with a new section on the Brazilian restingas in a chapter on coastal sand plains.
Understanding how photosynthesis responds to the environment is crucial for improving plant production and maintaining biodiversity in the context of global change. Covering all aspects of photosynthesis, from basic concepts to methodologies, from the organelle to whole ecosystem levels, this is an integrated guide to photosynthesis in an environmentally dynamic context. Focusing on the ecophysiology of photosynthesis how photosynthesis varies in time and space, responds and adapts to environmental conditions and differs among species within an evolutionary context the book features contributions from leaders in the field. The approach is interdisciplinary and the topics covered have applications for ecology, environmental sciences, agronomy, forestry and meteorology. It also addresses applied fields such as climate change, biomass and biofuel production and genetic engineering, making a valuable contribution to our understanding of the impacts of climate change on the primary productivity of the globe and on ecosystem stability.
This study was carried out to investigate the growth responses of medicinal plants such as Glehnia littoralis, Cryptotaenia japonica, Angelica gigas, Reynoutria japonica, Saururus chinensis, Houttuynia cordata, Ligularia fischeri, and Aralia cordata under 70%-shading and full sunlight conditions on a rooftop condition using artificial soil as a growth media. Glehnia littoralis, Cryptotaenia japonica, Ligularia fischeri, Saururus chinensis, and Houttuynia cordata showed better growth on plant height, leaf length, leaf width, petiole length and leaf number under full sunlight conditions on a rooftop condition. Cryptotaenia japonica and Houttuynia cordata had high value of Hunter`s a (red-green) under full sunlight, while had lower value of L(lightness) and b(blue-yellow) than those of 70% shading condition. As an index of plant stress response, Glehnia littoralis, Reynoutria japonica, Houttuynia cordata, Ligularia fischeri showed Fv/Fm values 0.79~0.84 under full sunlight in August, indicating low stress on plant growth. Therefore they seemed to be suitable medicinal plats for rooftop conditions. Ligularia fischeri and Reynoutria japonica showed better growth under 70% shading treatment in August, while showed high growth response under full sunlight conditions in September. The 70% shading treatment was effective for the growth of Angelica gigas, Reynoutria japonica, and Aralia cordata. Angelica gigas and Reynoutria japonica, however, showed better plant growth under full sunlight during summer. The results showed that Glehnia littoralis, Cryptotaenia japonica, Ligularia fischeri, Saururus chinensis, and Houttuynia cordat seemed to be suitable medicinal plants for rooftop garden where there is a full sunlight condition.
This study was conducted to investigate the chlorophyll contents, photosynthetic characteristics, chlorophyll fluorescence, and growth performance of Parasenecio firmus under changing light environment. Parasenecio firmus was grown under non-treated (full sunlight) and three different shading conditions (88~93%, 65~75% and 45%~55% of full sunlight) for the experiment. Total chlorophyll content, photochemical efficiency (Fv/Fm), T/R ratio, specific leaf area (SLA), leaf area ratio (LAR), and leaf weight ratio (LWR) were increased with increasing shading level, but decreased dark respiration. Therefore, light absorption and light utilization efficiency were improved under the low intensity light. Plants under 65~75% of full sunlight had best maximum photosynthetic rate and net apparent quantum yield in May. On the other hand, the non-treated plants had lower maximum photosynthetic rate, photochemical efficiency, and chlorophyll content than the treated ones. Parasenecio firmus considered to be a sciophyte, is fairly sensitive to high intensity light. If 88-93% of full sunlight lasts for a long period, photosynthetic capacity will be sharply decreased, though limiting light. These results suggest that growth of Parasenecio firmus adapted to 65~75% of full sunlight.
The photosynthetic performance of mangrove Rhizophora mucronata seedlings grown under seasonally full light (HL), 50 % shade (ML), and 80 % shade (LL) conditions was characterized by gas exchange, and chlorophyll fluorescence. The carboxylation efficiency significantly affected the seasonal change of the photosynthetic capacity. Temperature and light might have synergic effect on the carboxylation efficiency. The photosynthetic rate (PN) of R. mucronata seedlings under shade regimes, however, could not be attributed to variability in chlorophyll, C
i
, ΦPSII, ETR or qP values but more to differences in carboxylation efficiency, g
max, and E
max. HL and ML plants had higher PN, g
s and E than the LL ones. Nevertheless, LL leaves exhibited low photoinhibition susceptibility. The high non-photochemical quenching in HL leaves may show that applied light intensity probably exceeded the photosynthetic capability. The findings indicate that ML treatments provided the best condition to obtain such carbon fixation capacity.
Isotopes are forms of an element that differ in the number of neutrons. Isotopes function as natural dyes or colors, generally tracking the circulation of elements. Isotopes trace ecological connections at many levels, from individual microbes to whole landscapes. Isotope colors mix when source materials combine, and in a cyclic process that ecologists can appreciate, the process of isotope fractionation takes the mixed material and regenerates the sources by splitting or fractionating the mixtures. Elements and their isotopes circulate in the biosphere at large, but also in all smaller ecological plant, animal, or soil systems. Chapter 3 reviews this circulation for each of the HCNOS elements, then gives four short reviews that may stimulate you to think about how you could use isotopes in your own ecological research.
To investigate the adaptive capacity to a strong light environment when planted on degraded land, we examined photosynthetic properties in relation to photoinhibition for the sun-leaves of six tropical fruit tree species native to Malaysia before and after transplanting. The six species were: Bouea macrophylla (Bm), Callerya atropurpurea (Ca), Canarium pilosum (Cp), Cynometra cauliflora (Cc), Morinda citrifolia (Mc) and Syzygium sp. (Ssp), which produce edible fruit for endemic animals and birds, and are candidates for corridor plantations. Based on the measurements performed before transplanting, the degree of chronic photoinhibition indicated by the decrease in pre-dawn F (v)/F (m) was well associated with an accumulation of excessive excitation energy in PSII indicated by a decrease in photochemical quenching (qP). Among the species, Ca and Mc showed lower degrees of photoinhibition with higher qP. Higher electron transport rates (ETR) were observed with higher qP whereas there was no significant relationship between regulatory thermal dissipation (indicated by F-v/F-m - F-v(')/F-m(')) and qP. Energy dissipation via electron transport was suggested to be important in keeping qP high and preventing photoinhibition when compared among species. Cc and Bm showed lower ETR and higher susceptibility to photoinhibition before and after transplanting. New Cp and Mc leaves developed after transplanting showed increased area-based leaf nitrogen content (N (area)) and stomatal conductance (gs) compared with those before transplanting resulting in higher light-saturated net photosynthetic rates (A (max)) and ETR, and contributing to mitigate photoinhibition. In contrast to these species, Ca achieved high A (max) with a water conservative manner (indicated by its relatively lower gs), where the higher carboxylation efficiency accompanied with the higher N (area) allowed them to maintain relatively high A (max) and ETR at lower intercellular CO2 concentration.
The response of effective quantum yield of photosystem 2 (F/Fm) to temperature was investigated under field conditions (1 950 m a.s.l.) in three alpine plant species with contrasting leaf temperature climates. The in situ temperature response did not follow an optimum curve but under saturating irradiances [PPFD >800 mol(photon) m–2s–1] highest F/Fm occurred at leaf temperatures below 10C. This was comparable to the temperature response of antarctic vascular plants. Leaf temperatures between 0 and 15C were the most frequently (41 to 56%) experienced by the investigated species. At these temperatures, F/Fm was highest in all species (data from all irradiation classes included) but the species differed in the temperature at which F/Fm dropped below 50% (Soldanella pusilla >20C, Loiseleuria procumbens >25C, and Saxifraga paniculata >40C). The in situ response of F/Fm showed significantly higher F/Fm values at saturating PPFD for the species growing in full sunlight (S. paniculata and L. procumbens) than for S. pusilla growing under more moderate PPFD. The effect of increasing PPFD on F/Fm, for a given leaf temperature, was most pronounced in S. pusilla. Despite the broad diurnal leaf temperature amplitude of alpine environments, only in S. paniculata did saturating PPFD occur over a broad range of leaf temperatures (43 K). In the other two species it was half of that (around 20 K). This indicates that the setting of environmental scenarios (leaf temperaturePPFD) in laboratory experiments often likely exceeds the actual environmental demand in the field.
The synergistic effects of irradiance and salinity on leaf angle, the photochemical efficiency of photosystem II and photosynthetic pigment composition of mangroves were studied in a factorial experiment. Seedlings of Aegiceras corniculatum (L.) Blanco (Myrsinaceae) and Avicennia marina (Forstk.) Vierh var. australasica (Walp.) Moldenke (Avicenniaceae) were grown under salinity treatments (0, 5, 25, 50, 75, and 100% artificial seawater), in full sunlight or under shade cloth (transmitting 30 or 70% sunlight), during summer and autumn. Significant species’ differences and effects of salinity and growth irradiance were found for key measures. Depressions in F
v/F
m due to salinity and growth irradiance were chronic, they were least in 25% seawater and in 30% sunlight, and greater in low and high salinity, and higher irradiance. A diurnal depression of F
v/F
m was superimposed on the chronic depression, and was greater for Ae. corniculatum than Av. marina. Increases in leaf angle; and increases in the size, and de-epoxidation state of the xanthophyll cycle pigment pool afforded protection from adverse effects of excess excitation energy. Adverse effects of the highest salinities on β,β-carotene and β,ɛ-carotene biosynthetic pathways were suggested, particularly in Ae. corniculatum. The ecological significance of differences in species’ extent and temporal patterns of response are discussed.
The aim of this study was to investigate acclimation of micropropagated plants of Rhododendron ponticum subsp. baeticum to different irradiances and recovery after exposure to high irradiance. Plants grown under high (HL) or intermediate (IL)
irradiances displayed higher values of maximum electron transport rate (ETRmax) and light saturation coefficient (Ek) than plants grown under low irradiance (LL). The capacity of tolerance to photoinhibition (as assessed by the response of
photochemical quenching, qp) varied as follows: HL > IL > LL. Thermal energy dissipation (qN) was also affected by growth irradiance, with higher saturating values being observed in HL plants. Light-response curves
suggested a gradual replacement of qp by qN with increasing irradiance. Following exposure to irradiance higher than 1500 μmol m−2 s−1, a prolonged reduction of the maximal photochemical efficiency of PS 2 (Fv/Fm) was observed in LL plants, indicating the occurrence of chronic photoinhibition. In contrary, the decrease in Fv/Fm was quickly reverted in HL plants, pointing to a reversible photoinhibition.
Additional key wordselectron transport-photochemical quenching-photoinhibition-thermal energy dissipation
To elucidate mechanisms for tolerating sudden increases in light intensity following canopy gap formation, we investigated susceptibility to photoinhibition in the evergreen clonal plant bamboo, Sasa senanensis, and two deciduous broadleaf woody plants, Quercus mongolica, and Acer mono. We measured pre-dawn photochemical efficiency of photosystem II (F
v/F
m) in plants exposed to canopy gaps and in shade-grown plants through the month following gap formation. Photoinhibition (indicated by decreased F
v/F
m) was smallest in S. senanensis and largest in A. mono. S. senanensis had the highest area-based net CO2 assimilation rate (A
area) and electron transport rate (ETR) under high light conditions. This species also had the highest leaf mass per area (LMA) and leaf nitrogen content per area (N
area). Higher values of LMA and N
area under shade conditions probably contribute to circumvent photoinhibition through maintenance of a higher ETR capacity. Q. mongolica, a gap-dependent species, had properties intermediate between S. senanensis and A. mono; it appeared less susceptible to photoinhibition than the shade-tolerant A. mono. None of the species examined had increased photosynthetic capacity 1 month after gap formation, indicating that shade-grown leaves were unable to fully acclimate to increased light.
To determine the effects of elevated CO(2) concentration ([CO(2) ]) on the temperature-dependent photosynthetic properties, we measured gas exchange and chlorophyll fluorescence at various leaf temperatures (15, 20, 25, 30, 35 and 40°C) in 1-year-old seedlings of the Japanese white birch (Betula platyphylla var. japonica), grown in a phytotron under natural daylight at two [CO(2) ] levels (ambient: 400 µmol mol(-1) and elevated: 800 µmol mol(-1) ) and limited N availability (90 mg N plant(-1) ). Plants grown under elevated [CO(2) ] exhibited photosynthetic downregulation, indicated by a decrease in the carboxylation capacity of Rubisco. At temperatures above 30°C, the net photosynthetic rates of elevated-CO(2) -grown plants exceeded those grown under ambient [CO(2) ] when compared at their growth [CO(2) ]. Electron transport rates were significantly lower in elevated-CO(2) -grown plants than ambient-CO(2) -grown ones at temperatures below 25°C. However, no significant difference was observed in the fraction of excess light energy [(1 - q(P) )× F(v) '/F(m) '] between CO(2) treatments across the temperature range. The quantum yield of regulated non-photochemical energy loss was significantly higher in elevated-CO(2) -grown plants than ambient, when compared at their respective growth [CO(2) ] below 25°C. These results suggest that elevated-CO(2) -induced downregulation might not exacerbate the temperature-dependent susceptibility to photoinhibition, because reduced energy consumption by electron transport was compensated for by increased thermal energy dissipation at low temperatures.
This book begins with an introductory chapter, with consideration of the importance of geography, geology, floristic relationships and climate and vegetation patterns. Nine chapters follow, dealing with specific geographical areas: western Melanesia; eastern Melanesia; the subtropical islands in the New Zealand region; Micronesia; central Polynesia; western Polynesia; eastern Polynesia; northern Polynesia - the Hawaiian Islands; and the oceanic islands in the eastern Pacific. Each of the geographical chapters includes introductory remarks on the regional geography/geology and climate before detailed descriptions of the vegetation. A final chapter looks at the future of island vegetation.
The obligate shade plant, Tradescantia albiflora Kunth grown at 50 μmol photons · m(-2) s(-1) and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 μmol · m(-2) · s(-1), were exposed to photoinhibitory light conditions of 1700 μmol · m(-2) · s(-1) for 4 h at 22° C. Photosynthesis was assayed by measurement of CO2-saturated O2 evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 μmol · m(-2) · s(-1) was most resistant, with pea grown at 50 μmol · m(-2) · s(-1) showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (qp) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F'vF'm, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81-92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F'vF'm, since qp at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid ΔpH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to qp, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.
Efficiencies of photosynthetic energy conversion were determined in sun and shade leaves of several mangrove species, growing in an open intertidal habitat in North Queensland, by measuring the maximum photon yield of O2 evolution and 77K chlorophyll fluorescence characteristics. Preliminary meas- urements confirmed that mangrove leaves have low water potentials, low stomatal conductances and low light-saturated CO2 exchange rates. Mangrove sun leaves therefore received a very large excess of excitation energy.
Mangrove shade leaves had as high a photon yield of O2 evolution as non-mangrove leaves and their fluorescence characteristics were normal, showing that the energy conversion efficiency was unaffected by the high salinity. Mangrove sun leaves had markedly depressed photon yields and fluorescence was severely quenched showing that the efficiency of the photochemistry of photosystem II was reduced. The efficiency of energy conversion decreased with an increased radiation receipt. No such depression was detected in sun leaves of non-mangrove species growing in adjacent non-saline sites. Shading of man- grove sun leaves resulted in an increase in the efficiency of energy conversion but, in most species, more than 1 week was required for these leaves to reach the efficiency of shade leaves. Leaves exposed to direct sunlight had somewhat higher efficiencies in mangrove plants cultivated in 10% seawater as compared with full-strength seawater but the salinity of the culture solution had little effect on the increase in the efficiency upon shading.
Field and laboratory fluorescence measurements indicated that the reduced efficiency of energy conversion in mangrove sun leaves resulted from a large increase in the rate constant for radiationless energy dissipation in the antenna chlorophyll rather than from damage to the photosystem II reaction centres. We propose that this increase in radiationless energy dissipation serves to protect the reaction centres against damage by excessive excitation.
The phytosociological data of the mangrove forests in the Malay Peninsula were collected from 216 releves, and so they were phytosociologically divided into 6 community types as follows: (1) the Sonneratia alba/Avicennia alba community, (2) the Rhizophora apiculata community, (3) the Rhizophora apiculata/Bruguiera spp. community, (4) the Ceriops tagal/Xylocarpus spp. community, (5) the Lumnitzera littorea community and (6) the Excoecaria agallocha community. These 6 community types distributed from the marginal lower part to inner of the upper part and were well correlated to the level of tidal zone and the sediment types. Furthermore 13 transects were examined, our investigations were able to clarify the relationships between the floristic composition, the mangrove zonation, sediments type, major land use and location in the tidal range of the mangrove ecosystem in estuary and delta types.
Growth of selected Rhizophora apiculata (Rhizophoraceae) trees was monitored from 1920 through 1981 in a 0.16 ha plot of protected forest in the Matang Mangroves. Starting in 1950, the sample was increased to include monitoring the growth of all the trees more than 10 cm dbh (diameter at 1.3 m or above prop roots). All seedlings were censused by species and removed in 1920 and recensused in 1926, 1927, and 1981. Total above-ground dry weight (biomass) of the forest was estimated using stand tables and a regression equation of biomass on dbh calculated for destructively sampled R. apiculata trees from elsewhere in the Matang Mangroves. Net primary productivity (1950–1981) was calculated from estimated biomass increments and published litter-fall rates.Rhizophora apiculata has maintained its dominance of the plot since 1920 but Bruguiera gymnorrhiza (Rhizophoraceae) and several other more shade-tolerant species have steadily increased in abundance. Between the 1920's and 1981, R. apiculata declined in relative abundance in the seedling layer while B. parviflora and B. cylindrica increased.Mean mortality rate (1950–1981) for trees more than 10 cm dbh was 3.0% per year with a range of 1.3–5.4% per year. When trees fell over and hit other trees, the damaged trees usually died within 10 years. A major cause of mortality appeared to be sapwood-eating termites.Net primary productivity averaged 17.7 t/ha/year over the 1950–1981 observation period. Biomass ranged from 270 to 460 t/ha with a mean of 409 t/ha. It is suggested that Rhizophora spp. trees greater than 50 cm dbh and mangrove forests with total above-ground biomass exceeding 300 t/ha would develop in other areas outside of the region affected by hurricanes if the forest was protected from human disturbance.
Gas exchange characteristics were studied in two mangrove species, Aegiceras corniculatum (L.) Blanco and Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke, grown under a variety of salinity and humidity conditions. The assimilation rate was measured as a function of the intercellular CO(2) concentration [A(c(i)) curve]. The photosynthetic capacity decreased with increase in salinity from 50 to 500 millimolar NaCl, as shown by decline in both the initial linear slope and the upper plateau of the A(c(i)) curve, with A. corniculatum being the more sensitive species. The decline in photosynthetic capacity was enhanced by increase in the leaf to air vapor pressure difference from 6 to 24 millibars, but this treatment caused a decrease in only the upper plateau of the A(c(i)) curve. Stomatal conductance was such that the intercellular CO(2) concentration obtaining under normal atmospheric conditions occurred near the transition between the lower linear and upper plateau portions of the A(c(i)) curves. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate, which declined with increasing salinity and decreasing humidity. The marginal water cost of carbon assimilation was similar in most treatments, despite variation in the water loss/carbon gain ratio.
Micronesia covers a large section of the earth’s surface, most of it water (Fig. 5.1). There are approximately 161 islands, atolls, or closely associated groups of islands, but they are so small that altogether they constitute less than 2600 km2 of land (Douglas 1969). Stretching over 27° of latitude and 44° of longitude, Micronesia shows, as would be expected, great variation in climate and topography. The islands range from low coral atolls, through raised coral islands, a great variety of volcanic islands, to rare masses of metamorphic rock.
To analyze the sustainability and carrying capacity of a mangrove forest, we studied the profiles of species composition and biomass from the riverside to inland. A belt transect (25×180 m) divided into 9 plots was established in compartment 46, in the Matang Mangrove Forest Reserve, Perak, Peninsular Malaysia. Five tree species were distributed in the transect. Rhizophora apiculata showed the highest density, followed by Bruguiera parviflora, B. sexangula, R. mucronata and Avicenia alba. From the riverside to inland, the structure changed from pure R. apiculata stands to mixed Rhizophora - Bruguiera stands. The mean aboveground biomass of all the plots was 316 Mg ha -1. The largest and smallest volumes for biomass were 558 Mg ha -1 on the riverside and 144 Mg ha 1 inland , respectively. The values tended to be higher in R. apiculata-dominant stands. If a larger productive area could be set up where R. apiculata would predominate, i.e. an area at a lower ground level, a larger sustainable amount of biomass for firewood and charcoal use could be produced. The annual dead biomass, which is supplied to the forest floor as nutrients for aquatic life, was 5.1 Mg ha -1. While stocked biomass is more valuable to a local economy than the dead biomass, the contribution of the fallen trees (dead biomass) to habitats and nutrients for aquatic life must be evaluated exactly in the future.
In nature, the intensity of light, or photon flux density (PFD), shows great variation, both temporally and spatially. For example, a leaf in the under-story can experience changes in the incident PFD up to 100-fold within a few seconds (Chazdon and Pearcy 1991). Large changes in PFD are also experienced by exposed leaves when intermittent clouds obscure the sun. In addition, the total daily integrated photon flux varies greatly among habitats as well as within the canopy of a given plant stand. Plants on the floor of a tropical rainforest (Björkman and Ludlow 1972) or redwood forest (Björkman and Powles 1981) may receive as little as 1% of the daily photon flux above the plant canopy.
The effect of an acclimation to light stress during the growth of leaves on their response to high photon flux densities (PFDs) was characterised by quantifying changes in photosystem II (PSII) characteristics and carotenoid composition. During brief experimental exposures to high PFDs sun leaves exhibited: (a) much higher levels of antheraxanthin + zeaxanthin than shade leaves, (b) a greater extent of energy dissipation in the light-harvesting antennae, and (c) a greater decrease of intrinsic PSII efficiency that was rapidly reversible. During longer experimental exposures to high PFD, deep-shade leaves but not the sun leaves showed slowly developing secondary decreases in intrinsic PSII efficiency. Recovery of these secondary responses was also slow and inhibited by lincomycin, an inhibitor of chloroplast-encoded protein synthesis. In contrast, under field conditions all changes in intrinsic PSII efficiency in open sun-exposed habitats as well as understory sites with intense sunflecks appeared to be caused by xanthophyll cycle-dependent energy dissipation. Furthermore, comparison of leaves with different maximal rates of electron transport revealed that all leaves compensated fully for these differences by dissipating very different amounts of absorbed light via xanthophyll cycle-dependent energy dissipation, thereby all maintaining a similarly low PSII reduction state. It is our conclusion that an increased capacity for xanthophyll cycle-dependent energy dissipation is a key component of the acclimation of leaves to a variety of different forms of light stress, and that the response of leaves to excess light experienced in the growth environment is thus likely to be qualitatively different from that to sudden experimental exposures to PFDs exceeding the growth PFD.
1. The effects of a sudden increase in irradiance and the high leaf temperatures characteristic of a canopy gap environment were studied with chlorophyll fluorescence and gas-exchange measurements on shade- and sun-acclimated leaves of Alocasia macrorrhiza. 2. Photoinhibition occurred in both sun and shade leaves during a 2-h simulated gap treatment (1900 μ mol photons m-2 s-1) in which leaf temperatures rose to 40⚬C. Dissipation of excess energy was more efficient in sun leaves, which showed rapid quenching of fluorescence. The quantum yield of photosystem II as calculated from fluorescence in low light was considerably lower for shade than sun leaves after the gap treatment. 3. Fluorescence relaxation kinetics showed that sun leaves recovered overnight from photoinhibition even when leaf temperatures during treatment reached 40⚬C. By contrast, shade leaves given the same treatment had not recovered after 4 days in low light. Shade leaves given the same light treatment but held at 30⚬C instead of 40⚬C recovered within 4 days. Shade leaves treated at 40⚬C in moderate, saturating light (375 μ mol photons m-2 s-1) recovered overnight. Thirteen days of 3-h gap treatments on whole plants previously grown in shade showed that after initial depressions both fluorescence and photosynthetic capacity partially recovered. 4. Thus, the degree of photoinhibition and the potential for recovery are dependent on the synergistic roles of leaf temperatures and high light during initial gap conditions. Although quantum efficiency and photosynthetic capacity can be impaired by strong light and heat stress, shade leaves have significant capacity for repair and contribution to the whole-plant carbon budget during acclimation following gap formation.
The Syrian barley landrace Tadmor is adapted to semi-arid environments and
characterized by a reduced chlorophyll content (ca
−25% on a leaf area basis) compared to improved barley genotypes,
such as the European variety Plaisant. Tadmor leaves had reduced stomatal
conductance (gS ) compared to
Plaisant leaves both under well-watered conditions and during water stress.
Both Tadmor and Plaisant barley seedlings were progressively acclimated to
high temperature (39°C) and high photon flux density (1600 µmol
photons m −2 s −1 ).
During acclimation, the chlorophyll content of Tadmor leaves further decreased
whereas the carotenoid concentration remained virtually unchanged, leading to
a marked increase in the carotenoid:chlorophyll ratio. The chlorophyll content
of acclimated Tadmor leaves was reduced to approximately half of the
chlorophyll content of Plaisant leaves grown under the same conditions. Loss
of chlorophyll in Tadmor leaves was not observed when only one environmental
factor was increased (temperature or photon flux density). In the improved
variety, both chlorophylls and carotenoids accumulated during acclimation to
heat and strong light, leading to an almost constant carotenoid:chlorophyll
ratio. The loss of chlorophyll in the Syrian landrace was associated with
limited changes in the photosynthetic characteristics of the leaves (oxygen
evolution, electron transport quantum yield, chlorophyll antenna size of
photosystem II). Plaisant leaves, but not Tadmor leaves, exhibited symptoms of
oxidative damage during growth in strong light at high temperature. When the
stomata were closed, sudden exposure to bright light caused a smaller increase
in leaf temperature in Tadmor than in Plaisant. Taken together, our results
suggest that the ‘low chlorophyll’ feature of Syrian barley
landraces is related to their drought adaptation which is manifested by a low
g S : the very low chlorophyll content decreases leaf
absorbance which, in turn, reduces the potentially damaging heating effect of
high solar radiation in droughted plants whose stomata are closed.
Photoinhibition was examined in naturally exposed willow leaves in the field. In the afternoon on clear and warm days, the quantum yield of electron transport, derived from gas exchange data, was decreased by 28%. Besides this photoinhibition, decreases in the photosynthetic capacity and in the stomatal conductance were also observed. Of these three limitations of carbon assimilation, photoinhibition was the major one at limiting light only.
To investigate the generality of photoinhibition, shade- and sun-acclimated leaves of fourteen different species were compared in a laboratory study. Photoinhibition was quantified by fluorescence measurements following exposure to moderate and high light for 30 min. The extent of photoinhibition was inversely related to the photochemical quenching, qp, during exposure (the proportion of open PS II traps). This relationship was the same independent of the species, the light-acclimation state of the leaf and the light intensity. However, sun- and shade-acclimated leaves occupied opposite sides of the relationship: the sun-leaves showed lower photoinhibition and higher qp. The sun-leaves were also more competent than shade-leaves by showing faster recovery from a given level of photoinhibition.
Use of leaf meters to provide an instantaneous assessment of leaf chlorophyll has become common, but calibration of meter output into direct units of leaf chlorophyll concentration has been difficult and an understanding of the relationship between these two parameters has remained elusive. We examined the correlation of soybean (Glycine max) and maize (Zea mays L.) leaf chlorophyll concentration, as measured by organic extraction and spectrophotometric analysis, with output (M) of the Minolta SPAD-502 leaf chlorophyll meter. The relationship is non-linear and can be described by the equation chlorophyll (μmol m−2)=10(M0.265), r
2=0.94. Use of such an exponential equation is theoretically justified and forces a more appropriate fit to a limited data set than polynomial equations. The exact relationship will vary from meter to meter, but will be similar and can be readily determined by empirical methods. The ability to rapidly determine leaf chlorophyll concentrations by use of the calibration method reported herein should be useful in studies on photosynthesis and crop physiology.
The photosynthetic response to light can be accurately defined in terms of (1) the initial slope (quantum yield); (2) the asymptote (light-saturated rate); (3) the convexity (rate of bending); and (4) the intercept (dark respiration). The effects of photoinhibition [which damages the reaction centre of photosystem II (PSII)] on these four parameters were measured in optically thin cultures of green plant cells (Chlamydomonas reinhardtii). The convexity of the light-response curve decreased steadily from a value of 0.98 (indicating a sharply bending response) to zero (indicating Michaelis-Menten kinetics) in response to increasing photoinhibition. Photoinhibition was quantified from the quantum yield of inhibited cells relative to that of control cells. The quantum yield was estimated by applying linear regression to low-light data or by fitting a non-rectangular hyperbola. Assuming the initial slope is linear allowed comparison with earlier work. However, as the convexity was lowered this assumption resulted in a significant underestimate of the true quantum yield. Thus, the apparent level of photoinhibition required for a zero convexity and the initial decrease in light-saturated photosynthesis depended upon how the quantum yield was estimated. If the initial slope of the light response was assumed to be linear the critical level of inhibition was 60%. If the linear assumption was not made, the critical level was 40%. At the level of inhibition where the convexity reached zero, the light-saturated rate of photosynthesis also began to decrease, indicating that this level of inhibition caused photosynthesis to be limited at all light intensities by the rate of PSII electron transport. At this level of inhibition the Fm-Fi signal (where Fm is maximal chlorophyll fluorescence and Fi is intermediate chlorophyll fluorescence of dark adapted cells; Briantais et al. 1988) from the fluorescence induction curve was zero and the Fi-Fo signal (where Fo is initial chlorophyll fluorescence of dark adapted cells) was 30% of the control, indicating dramatic reduction or complete elimination of one type of PSII. These data do not contradict published mathematical models showing that the ratio of the maximum speed of electron transport in PSII relative to the maximum speed of plastoquinone electron transport can determine the convexity of the photosynthetic response to light.
Six types of mangrove forests were distinguished on Kosrae Island (50°20’ N.L.; 163°00’ E.L.) and Pohnpei Island (6°55’ N.L.; 158°14’ E.L.) in Micronesia and Bohol Island (10°00’ N.L.; 124°30’ E.L.) in the Philippines based on phytosociological investigations. They are the Rhizophora stylosa forest on an inorganic habitat along the seaward fringe of a mangrove area, the Nypa fruticans thicket and the Barringtonia racemosa forest supported by clay deposits at the landward fringe of a mangrove region, and the Rhizophora apiculata-Avicennia marina forest, the Sonneratia alba-Bruguiera gymnorrhiza forest and the Xyrocarpus granatum-B. gymnorrhiza forest characteristically inhabiting peaty habitats. Accumulation of mangrove peat should be limited to a range corresponding to the upper half of the intertidal zone because mangrove forests themseves are restricted to this range. This range is estimated to be 75 cm or so in the areas investigated. A habitat with a peat layer equivalent to this range in thickness was usually found under the S. alba-B. gymnorrhiza forest. This type of forest is thought to have developed under the present, stable sea level condition through autogenic succession from the R. stylosa forest. On the other hand, a much thicker peat layer supporting the X. granatum-B. gymnorrhiza forest was found in the investigated area. Development of such a thick peat layer is assumed to have been proceeded by a rise in sea level, followed by filling up of the area with organic matter provided by the mangrove forest itself. Thus, this type of forest was considered to have been formed from the S. alba-B. gymnorrhiza forest through an autogenic process of succession in spite of the external effect of a rise in sea level.
The susceptibility to photoinhibition of tree species from three different successional stages were examined using chlorophyll fluorescence and gas exchange techniques. The three deciduous broadleaf tree species were Betula platyphylla var. japonica, pioneer and early successional, Quercus mongolica, intermediate shade-tolerant and mid-successional, and Acer mono, shade-tolerant and late successional. Tree seedlings were raised under three light regimes: full sunlight (open), 10% full sun, and 5% full sun. Susceptibility to photoinhibition was assessed on the basis of the recovery kinetics of the ratio of vaviable to maximum fluorescence (Fv/Fm) of detached leaf discs exposed to about 2000 μmol m−1 s−1 photon flux density (PFD) for 2 h under controlled conditions (25 to 28 °C, fully hydrated). Differences in susceptibility to photodamage among species were not significant in the open and 10% full sun treatments. But in 5% full sun, B. platyphylla sustained a significantly greater photodamage than other species, probably associated with having the lowest photosynthetic capacity indicated by light-saturated photosynthetic rate (B. platyphylla, 9·87, 5·85 and 2·82; Q. mongolica, 8·05, 6·28 and 4·41; A. mono, 7·93, 6·11 and 5·08 μmol CO2 m−1 s−1for open, 10% and 5% full sun, respectively). To simulate a gap formation and assess its complex effects including high temperature and water stress in addition to strong light on the susceptibility to photoinhibition, we examined photoinhibition in the field by means of monitoring ΔF/F′m on the first day of transfer to natural daylight. Compared with ΔF/F′m in AM, the lower ΔF/F′m in PM responding to lower PFD following high PFD around noon indicated that photoinhibition occurred in plants grown in 10 and 5% full sun. The diurnal changes of ΔF/F′m showed that Q. mongolica grown in 5% full sun was less susceptible to photoinhibition than A. mono although they showed little differences both in photosynthetic capacity in intact leaves and susceptibility to photoinhibition based on leaf disc measurements. These results suggest that shade-grown Q. mongolica had a higher tolerance for additional stresses such as high temperature and water stress in the field, possibly due to their lower plasticity in leaf anatomy to low light environment.
The effects of strong light in combination with elevated temperatures on the photosynthetic system were examined in 4 dipterocarp tree species with ecologically different habitats. The 4 dipterocarp tree species were: Shorea platyclados originated from upper dipterocarp forests, Shorea parvifolia– lowland and hill dipterocarp forests, Shorea assamica– lowland dipterocarp forests, and Dipterocarpus oblongifolius– riparian fringes. S. platyclados and D. oblongifolius have higher growth and survival rates in open sites than S. parvifolia and S. assamica. Tolerance of high temperature among the species was assessed by determining the critical temperatures (Tc) at which the minimal fluorescence (Fo) began to rise sharply. This was measured by exposing plants to an increasing temperature of about 1°C min−1. The intrinsic thermotolerance of the thylakoid membrane appears to be the highest for D. oblongifolius (Tc=46.4°C), intermediate for S. platyclados (45.7°C), and lowest for S. parvifolia and S. assamica (45.2 and 45.3°C, respectively). The temperature-dependent efficiency of PSII electron transport (ΔF/F′m), photochemical quenching (qP), and the efficiency of light capture of open PSII (F′v/F′m) were measured at the photosynthetic steady state at least 10 min after the light exposure (180 μmol m−2 s−1 PFD). Stable temperature responses of ΔF/F′m and qP were observed in S. platyclados and D. oblongifolius, while those in S. parvifolia and S. assamica were more temperature-dependent and severely affected at 45°C. Little difference was observed in temperature-dependent F′v/F′m among species. Photoinhibitory light exposure (1600 μmol m−2 s−1 PFD) for 2 h at 40°C had little effect on the recovery kinetics from photoinhibition of S. platyclados and D. oblongifolius compared with those at 35°C. In contrast, the recovery from photoinhibition was retarded in S. parvifolia and S. assamica. These findings suggest that even at 40°C, a temperature below Tc, an exposure to strong light exacerbated photoinhibition in S. parvifolia and S. assamica corresponding to the closure of PSII reaction centers, as indicated by the decrease in qP at this temperature. Thus, S. platyclados and D. oblongifolius, which occur at uplands and riparian fringes with frequent disturbances, are suggested to have higher photosynthetic tolerance to elevated temperatures contributing to a circumvention of photoinhibition.
Net CO2 exchange and in vivo chlorophyll fluorescence were studied in mangrove (Rhizophora stylosa) leaves at a field site in Western Australia, and leaf samples were collected for the analysis of enzymes and substrates potentially involved in anti-oxidant photoprotection. Photosynthesis saturated at 900 μmol quanta m−2 s−1 and at no more than 7.5 μmol CO2 m−2 s−1. However, fluorescence analysis indicated no chronic photoinhibition: Fv:Fm was 0.8 shortly after sunset, and quantum efficiencies of PSII were high up to 500 μmol quanta m−2 s−1. Electron flow through PSII was more than 3 times higher than electron consumption through Calvin cycle activity, however, even with photorespiration and temperature-dependent Rubisco specificities taken into account.
Acknowledging the growing body of literature attributing a role to antioxidant systems in photoprotection, we also assayed the activities of superoxide dismutase (SOD) and several enzymes potentially involved in H2O2 metabolism. Their levels of maximal potential activity were compared with those in greenhouse-grown mangroves (R. mangle), and growth chamber-grown peas. Monodehydroascorbate reductase activities were similar in all species, and glutathione reductase was lower, and ascorbate peroxidase ∼40% higher, in the mangroves. SOD activities in field-grown mangroves were more than 40 times those in peas.
Our results support the hypothesis that O2 may be a significant sink for photochemically derived electrons under field conditions, and suggest an important role for O2− scavenging in photoprotection. However, when relative patterns are compared between species, imbalances between SOD and the other enzymes in the mangroves suggest that more components of the system (e.g. phenolics or peroxidases) are yet to be identified.
Analyses of chlorophyll fluorescence and photosynthetic oxygen evolution were conducted to understand why cold-hardened winter rye (Secale cereale L.) is more resistant to photoinhibition of photosynthesis than is non-hardened winter rye. Under similar light and temperature conditions, leaves of cold-hardened rye were able to keep a larger fraction of the PS II reaction centres in an open configuration, i.e. a higher ratio of oxidized to reduced QA (the primary, stable quinone acceptor of PSII), than leaves of non-hardened rye. Three fold-higher photon fluence rates were required for cold-hardened leaves than for non-hardened leaves in order to establish the same proportion of oxidized to reduced QA. This ability of cold-hardened rye fully accounted for its higher resistance to photoinhibition; under similar redox states of qa cold-hardened and non-hardened leaves of winter rye exhibited similar sensitivities to photoinhibition. Under given light and temperature conditions, it was the higher capacity for light-saturated photosynthesis in cold-hardened than in non-hardened leaves, which was responsible for maintaining a higher proportion of oxidized to reduced QA. This higher capacity for photosynthesis of cold-hardened leaves also explained the increased resistance of photosynthesis to photoinhibition upon cold-hardening.
Photoinhibition of photosynthesis was studied in young (but almost fully expanded) and mature canopy sun leaves of several tropical forest tree species, both under controlled conditions (exposure of detached leaves to about 1.8 mmol photonsm-2s-1) and in the field. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence emission (FV/FM) and also by gas-exchange measurements. For investigations in situ, young and mature leaves with similar exposure to sunlight were compared. The results show a consistently higher degree of photoinhibition in the young leaves. In low light, fast recovery was observed in both types of leaves in situ, as well as in the laboratory. The fluorescence parameter 1 — FS/FM (where FS = stationary fluorescence and fM = maximum fluorescence during illumination) was followed in situ during the course of the day in order to test its suitability as a measure of the photosynthetic yield of photosystem II (PSII). Electron-transport rates were calculated from these fluorescence signals and compared with rates of net CO2 assimilation. Measurements of diurnal changes in PSII yield confirmed the increased susceptibility of young leaves to photoinhibition. Calculated electron transport qualitatively reflected net CO2 uptake in situ during the course of the day. Photosynthetic pigments were analyzed in darkened and illuminated leaves. Young and mature leaves showed the same Chl a/b ratio, but young leaves contained about 50% less Chl a + b per unit leaf area. The capacity of photosynthetic O2 evolution per unit leaf area was decreased to a similar extent in young leaves. On a Chl basis, young leaves contained more -carotene, more xanthophyll cycle pigments and, under strong illumination, more zeaxanthin than mature leaves. The high degree of reversible photoinhibition observed in these young sun leaves probably represents a dynamic regulatory process protecting the photosynthetic apparatus from severe damage by excess light.
Mangroves have similar xanthophyll cycle components/chlorophyll ratios [i.e. (V+A+Z)/chl] to other plant species. (V+A+Z)/chl
ratios were sensitive to the light environment in which leaves grew, decreasing as light levels decreased over a vertical
transect through a forest canopy. The (V+A+Z)/chl ratio also varied among species. However, in sun leaves over all species,
the (V+A+Z)/chl ratios correlate with the proportion of leaf area displayed on a horizontal plane, which is determined by
leaf angle. Thus, leaf angle and the xanthophyll cycle may both be important in providing protection from high light levels
in mangrove species. A canopy survey assessed whether (V+A+Z)/chl ratios could be correlated with species dominance of exposed
positions in forest canopies.Rhizophora mangroves, with near-vertical leaf angles, andBruguiera parviflora, with small, horizontal, xanthophyllrich leaves, dominated the canopy, whileB. gymnorrhiza, a species with large, horizontally arranged leaves, was less abundant at the top of the canopy. Thus, two different strategies
for adapting to high solar radiation levels may exist in these species. The first strategy is avoidance through near vertical
leaf angles, and the second is a large capacity to dissipate energy through zeaxanthin. The (V+A+Z)/chl ratio was also negatively
correlated with the epoxidation state of the xanthophyll cycle pool (the proportion present as violaxanthin and half that
present as antheraxanthin) at midday. This suggested that the requirement for dissipation of excess light (represented by
the midday epoxidation state) may influence the (V+A+Z)/chl ratio.
Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO2 assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO2 assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO2 assimilation rate resulted in constant and similar intercellular CO2 concentrations for leaves exposed to photon flux densities above 800 molm-2s-1 in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO2 assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO2 concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.
Photosynthetic gas exchange properties of leaves of the mangrove, Rhizophora stylosa Griff., were investigated in order to assess its productivity and gain some insight into the constraints set upon it by the saline habitat. Mature trees of this dominant species were studied in their natural, tidal-forest environment at Hinchinbrook Is., North Queensland for two periods during the dry season. Individual leaves were enclosed in a chamber wherein environmental conditions were varied. CO2 assimilation, transpiration and environmental parameters were monitored during daylight hours by instrumentation housed in a mobile laboratory mounted on a barge. Analysis of the daily course of leaf gas exchange revealed a CO2 assimilation capacity comparable with that of many glycophytic trees. Photosynthesis was strongly influenced by leaf temperature as well as photon flux density. There was a strong and steadily increasing inhibition of gas exchange as leaf temperatures and, consequently, the leaf to air VPD increased. CO2 assimilation rates and leaf conductances to water vapour diffusion were strongly correlated, resulting in nearly constant internal CO2 concentrations in the leaves under the full range of conditions. The effect of leaf orientation in minimizing the leaf-to-air temperature difference was striking. The close coordination between stomatal conductance and CO2 assimilation rate in this mangrove results in high water use efficiency. This sparing use of water may be an important factor underlying the high salinity tolerance of mangroves.
Data on stand structure and rates of photosynthesis were used to estimate net canopy carbon fixation and carbon accumulation as living biomass in mangrove forests in Hinchinbrook Channel, Australia. Total annual canopy net carbon fixation was estimated to be about 29tCha–1yr–1. This equates to about 204,000tCyr–1 for all mangrove forests in Hinchinbrook Channel. Of this, only about 12% was stored as living plant biomass. Although it is not yet possible to present a robust carbon balance for mangrove trees, the remainder is presumably lost through plant respiration, litter fall, root turnover and exudation of organic compounds from roots.
Belowground carbon storage was examined for mangrove forests on Pohnpei Island, Micronesia. Stored carbon in a coral reef-type mangrove habitat consisting of a 2 m thick mangrove peat layer, which is a type of mangrove habitat in tropical Pacific islands, was estimated at 1300 t C ha–1. The carbon burial rate during the phase of gradual sea-level rise, which was calculated at 93 g m–2 year–1 between 1800 and 1380 years bp using the medians of the radiocarbon ages, was significantly higher than that between 1380 years bp and present in a stable sea-level phase.
Using the sites of Pagbilao, the Philippines and Pohnpei Island, the Federated States of Micronesia, zonation and development process of mangrove habitats on tidal flats situated in the geomorphic environment excluding estuary, delta, and lagoon or backmarsh behind barrier or beach ridge were discussed from the viewpoint of geomorphology.Zonations of the mangrove forests were observed from seaward to landward in both areas. Most of the zones correspond with the variations of the ground level or deposit. Mangrove peat which has a thickness of about 2 meters was deposited in the main part of the mangrove habitats in both areas. On the other hand, some large Sonneratia alba were observed in the Rhizophora apiculata habitat on Pohnpei Island. The authors presumed that some of the large S. alba have survived by regeneration from fallen stems since the mangrove forest developed on the present site.The maximum depth of the mangrove peat layer reaches 1.7 meter below the present sea level in Pagbilao and over 2.5 meters at Pohnpei Island. The bottom of the mangrove peat was dated at about 2,000 y.B.P. in both areas by the radiocarbon method. The mangrove peat depositional areas have not been moved during the last 2,000 years. Therefore, the mangrove forests seem to have grown in the present sites since 2,000 y.B.P. and accumulated peat in connection with the subsequent sea-level rise. xx]Nomenclature: Scientific names for mangroves follow Tomlinson (1986). xx]Papers presented at the Vth INTECOL Congress at Yokohama 1990.
The importance of photoprotective strategies for Photosystem (PS) II function under all light regimes was determined from the content of functional PS II, measured by repetitive flash yield of oxygen evolution, in leaves of pea (Pisum sativum L.) grown under 50 (low light), 250 (medium light), and 650 (high light) μmol photons m−2 s−1. The modulation of PS II functionality in vivo was induced in 1.1% CO2 after infiltration of leaves with water (control), nigericin (a lipophilic uncoupler) or dithiothreitol (DTT, inhibitor of violaxanthin to zeaxanthin conversion) through the cut petioles of leaves of 22–24 day-old plants. In all nigericin-treated pea leaves, photoinactivation of PS II was greatly increased with increasing photon exposure (mol photons m−2). This nigericin-induced increase of photoinactivation of PS II was greater than that induced by DDT in medium- and high-light pea leaves, but comparable in low-light peas. In low-light peas during steady-state photosynthesis, the development of non-photochemical quenching of chlorophyll fluorescence (NPQ, measured as ) was lowest, accompanying the highest reduction state of PS II (measured by photochemical quenching, qP). Further, the susceptibility of PS II to light stress, estimated as [Park et al., Plant Cell Physiol., 36 (1995) 1163–1167], was highest in low-light peas. The decline of chlorophyll fluorescence from maximum (Fm) to steady-state level during induction phase of chlorophyll fluorescence was retarded by nigericin treatment, with a greater inhibitory effect in high- and medium- than low-light pea leaves. From these results, we suggest that the greater susceptibility of low-light peas to light stress than medium- and high-light peas is ascribed to lower capacities for both the utilization of absorbed light by photosynthesis and for non-radiative dissipation of absorbed light as heat.
Measurements of the quantum yields of chlorophyll fluorescence and CO2 assimilation for a number of plant species exposed to changing light intensity and atmospheric CO2 concentrations and during induction of photosynthesis are used to examine the relationship between fluorescence quenching parameters and the quantum yield of non-cyclic electron transport. Over a wide range of physiological conditions the quantum yield of non-cyclic electron transport was found to be directly proportional to the product of the photochemical fluorescence quenching (qQ) and the efficiency of excitation capture by open Photosystem II (PS II) reaction centres (Fv/Fm). A simple fluorescence parameter, ΔφF/φFm, which is defined by the difference in fluorescence yield at maximal φFm, and steady-state φFs, divided by φFm, can be used routinely to estimate changes in the quantum yield of non-cyclic electron transport. It is demonstrated that both the concentration of open PS II reaction centres and the efficiency of excitation capture by these centres will determine the quantum yield of non-cyclic electron transport in vivo and that deactivation of excitation within PS II complexes by non-photochemical processes must influence the quantum yield of non-cyclic electron transport.
Immunocompetence (i.e., the ability to produce an immune response to pathogens) can be predicted to influence the chances that organisms have to survive and reproduce. In this study we simulated a challenge to the immune systems of male barn swallows (Hirundo rustica) by injecting them intraperitoneally with a multigenic antigen, sheep red blood cells, and we analyzed long-term survival in relation to their immunocompetence. Males were assigned to four groups that differed for the treatment of the length of the outermost tail feathers, a sexually dimorphic ornamental character that is currently under directional sexual selection. Immunocompetence was measured as change of concentration of gamma globulins relative to plasma proteins. The intensity of the immune response was independent of age. Males that showed the highest short-term response to sheep red blood cells were more likely to survive until the breeding season following that in which they had been inoculated, a pattern consistently observed within each experimental group. Males with comparatively long tails were more likely to survive than those with short tails. To our knowledge, the results of this study are the first to demonstrate that immunocompetence can predict long-term survival in a free-ranging vertebrate. Moreover, they are compatible with current models of parasite-mediated sexual selection because long-tailed males are more immunocompetent than short-tailed ones, and females, by preferring to mate with the most ornamented males, may acquire the "good genes" for high immunocompetence and, hence, for high viability of their offspring.
We investigated the effect of photosynthetic electron transport and of the photosystem II (PSII) chlorophyll (Chl) antenna size on the rate of PSII photoinhibitory damage. To modulate the rate of photosynthesis and the light-harvesting capacity in the unicellular chlorophyte Dunaliella salina Teod., we varied the amount of inorganic carbon in the culture medium. Cells were grown under high irradiance either with a limiting supply of inorganic carbon, provided by an initial concentration of 25 mM NaHCO3, or with supplemental CO2 bubbled in the form of 3% CO2 in air. The NaHCO3-grown cells displayed slow rates of photosynthesis and had a small PSII light-harvesting Chl antenna size (60 Chl molecules). The half-time of PSII photodamage was 40 min. When switched to supplemental CO2 conditions, the rate of photodamage was retarded to a t1/2 = 70 min. Conversely, CO2-supplemented cells displayed faster rates of photosynthesis and a larger PSII light-harvesting Chl antenna size (500 Chl molecules). They also showed a rate of photodamage with t1/2 = 40 min. When depleted of CO2, the rate of photodamage was accelerated (t1/2 = 20 min). These results indicate that the in-vivo susceptibility to photodamage is modulated by the rate of forward electron transport through PSII. Moreover, a large Chl antenna size enhances the rate of light absorption and photodamage and, therefore, counters the mitigating effect of forward electron transport. We propose that under steady-state photosynthesis, the rate of light absorption (determined by incident light intensity and PS Chl antenna size) and the rate of forward electron transport (determined by CO2 availability) modulate the oxidation/reduction state of the primary PSII acceptor QA, which in turn defines the low/high probability for photodamage in the PSII reaction center.
The effects of photoinhibition on the photosynthetic light-response curve of green plant cells (Chlamydomonas reinhardtii) Photoinhibition of photosynthesis in nature Influence of solar radiation and leaf angle on leaf xanthophyll concentrations in mangroves
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Photosynthetic gas exchange of the mangrove, Rhizophora stylosa Griff., in its natural environment Photosynthetic and stomatal responses of two mangrove species, Aegiceras corniculatum and Avicennia marina, to long term salinity and humidity conditions
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TJ, Muller GJ (1985) Photosynthetic gas exchange of the mangrove, Rhizophora stylosa Griff., in its natural environment. Oecologia 65: 449–455 Ball MC, Farquhar GD (1984) Photosynthetic and stomatal responses of two mangrove species, Aegiceras corniculatum and Avicennia marina, to long term salinity and humidity conditions. Plant Physiol 74: 1–6 Baroli
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Site environments and stand structure of the mangrove forests on Pohnpei Island, Micronesia
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