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Quantum Yields for CO2 Uptake in C3 and C4 Plants: Dependence on Temperature, CO2, and O2 Concentration
Abstract
The quantum yields of C(3) and C(4) plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O(2) and in 2% O(2). At 30 C, the quantum yields of C(3) plants averaged 0.0524 +/- 0.0014 mol CO(2)/absorbed einstein and 0.0733 +/- 0.0008 mol CO(2)/absorbed einstein under 21 and 2% O(2). At 30 C, the quantum yields of C(4) plants averaged 0.0534 +/- 0.0009 mol CO(2)/absorbed einstein and 0.0538 +/- 0.0011 mol CO(2)/absorbed einstein under 21 and 2% O(2). At 21% O(2), the quantum yield of a C(3) plant is shown to be strongly dependent on both the intercellular CO(2) concentration and leaf temperature. The quantum yield of a C(4) plant, which is independent of the intercellular CO(2) concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C(3) plants are due to changes in the O(2) inhibition. The evolutionary significance of the CO(2) dependence of the quantum yield in C(3) plants and the ecological significance of the temperature effects on the quantum yields of C(3) and C(4) plants are discussed.
... Temperature and precipitation are believed to have an influence on these forest ecosystem components. The response of plant species is different to temperature and CO 2 (Collatz., et al 1992) and in photosynthetic CO 2 fixation (Cerling et al., 1993;Ehleringer and Bjorkman, 1977). The rate of leaf photosynthesis increases as leaf temperature increases to an optimum, and then decreases as temperature rises further (Figure 4). ...
... Maize, sorghum, sugarcane, and teff are few of among C 4 plants category. Ehleringer and Bjorkman (1977) explain that the assimilation of solar energy into carbohydrates decreases while temperature decreases in C 3 plants. Increase in CO 2 has a positive and negative effect on plants. ...
... Responses of C3 and C4 plants of CO2 (left) and temperature (right) (source:Collatz et al. (1992);Ehleringer and Bjorkman (1977)) ...
... However, temperature is a less likely candidate than light to explain the lost photosynthetic efficiency of shaded leaves seen at the plot centre in the present study. In C 3 plants, φCO 2 max,abs is highly temperature-sensitive, primarily due to increased photorespiration at high temperatures (Ehleringer and Bjorkman, 1977;Long and Spence, 2013). In contrast, due to the C 4 cycle's suppression of photorespiration, φCO 2 max,abs has been found to be constant with temperature from 15 to 40 • C in C 4 species such as Atriplex rosea (Ehleringer and Bjorkman, 1977) and Alloteropsis semialata (Osborne et al., 2008). ...
... In C 3 plants, φCO 2 max,abs is highly temperature-sensitive, primarily due to increased photorespiration at high temperatures (Ehleringer and Bjorkman, 1977;Long and Spence, 2013). In contrast, due to the C 4 cycle's suppression of photorespiration, φCO 2 max,abs has been found to be constant with temperature from 15 to 40 • C in C 4 species such as Atriplex rosea (Ehleringer and Bjorkman, 1977) and Alloteropsis semialata (Osborne et al., 2008). Although loss of φCO 2 max,abs has been observed in NADP-ME C 4 grasses such as Z. mays due to photodamage during long-term exposure to a combination of high light and cool temperatures (<15 • C) (Long and Spence, 2013), this is unlikely to have occurred in the warm summer months during which the present study took place, with maximum daily air temperatures ranging from 19.5 to 33 • C at the time measurements were taken. ...
... The reaction of O 2 produces compounds that need to be recycled in the energetically costly photorespiration pathway (Nisbet et al., 2007). In C 3 plants, Rubisco is in direct contact with atmospheric gases, and photorespiration can become consequential in conditions that decrease the relative concentration of CO 2 , including high temperature, aridity and salinity (Ehleringer and Bjorkman, 1977;Skillman, 2007). C 4 plants tackle this problem by segregating primary carbon fixation from the enzyme Rubisco into two cell types . ...
... Temperature and precipitation are believed to have an influence on these forest ecosystem components. The response of plant species is different to temperature and CO 2 (Collatz., et al 1992) and in photosynthetic CO 2 fixation (Cerling et al., 1993;Ehleringer and Bjorkman, 1977). The rate of leaf photosynthesis increases as leaf temperature increases to an optimum, and then decreases as temperature rises further (Figure 4). ...
... Maize, sorghum, sugarcane, and teff are few of among C 4 plants category. Ehleringer and Bjorkman (1977) explain that the assimilation of solar energy into carbohydrates decreases while temperature decreases in C 3 plants. Increase in CO 2 has a positive and negative effect on plants. ...
... Responses of C3 and C4 plants of CO2 (left) and temperature (right) (source:Collatz et al. (1992);Ehleringer and Bjorkman (1977)) ...
... In addition, under limiting CO 2 conditions, photorespiration is an effective way of dissipating excess photochemical energy. This in turn prevents photoinhibition, a deleterious effect of the excess light energy on photosynthesis, especially on PS2 (Powles et al. 1979;Ehleringer and Björkman 1977;Osmond 1981;Bradbury and Baker 1986;Baker 2008). The energetics of photosynthesis are significantly affected through the photoinhibition mechanism, affecting chloroplast thylakoids (Osmond 1981). ...
... In spite of the advantages or importance of photorespiration as mentioned above, limiting photorespiration using low O 2 (2%) conditions (Osmond 1981;Powles et al. 1979;Ehleringer and Björkman 1977) enhanced the plant's biomass in the model C 3 plants. The installation of any of the nine different photorespiratory bypasses (known to date) in the C 3 plants resulted in enhanced biomass (Kebeish et al. 2007;Nölke et al. 2014;Maier et al. 2012;Carvalho et al. 2011;South et al. 2019;Shen et al. 2019;Wang et al. 2020;Xu et al. 2023;Roell et al. 2021). ...
Developing C4 rice is one of the global research challenges for yield improvement. In the optimal environment, the key difference between C3 and C4 plants with reference to biomass accumulation is photorespiration. Photorespiration is important for a plant’s survival. In spite of the high energy cost and carbon loss, diversion of a significant part of carbon from photorespiration to enrich CO2 concentration (preventing carbon loss) was opted for. Installation of photorespiratory bypasses was reported to improve biomass and yield in C3 plants. The contribution of non-foliar photosynthesis to yield improvement was well documented. However, its underlying genetic differences, when compared to foliar photosynthesis, are a research gap. In three rice genotypes (APO, BAM4234, and CROSSA), we compared the expression levels (for genes associated with photosynthesis and photorespiration) between the photosynthetic non-foliar (3–5-day old developing grains and peduncle) and foliar (flag leaf) organs to understand their differential expression pattern using an RNA-seq approach. Significant downregulation of the genes of photorespiration was observed in non-foliar photosynthetic tissue (3–5 dpa old developing grains) when compared to the flag leaves. Simultaneously, our study also revealed significant upregulation of the chloroplastic pyruvate dehydrogenase (cpPDC, BGIOSGA015796) gene in developing grains, when compared to the flag leaf, in all three genotypes. The occurrence of an in planta photorespiratory bypass in the photosynthetic tissues of the developing grains in rice is proposed. Enhanced expression levels for the cpPdc gene in the foliar tissues will potentially install a photorespiratory bypass for enhanced biomass accumulation and thereby yield.
... 59), the sensitivity of A j to CO 2 therefore represents a conservative approach to incorporate a CO 2 sensitivity of LUE 37 in RS estimates of photosynthesis. Note that we also make the conservative assumption that C 4 plants operate at or near CO 2 saturation 60 . ...
... where K c and K o are the Michaelis-Menten coefficient of RuBisCO for carboxylation and oxygenation, respectively, expressed in partial pressure units and P o is the partial pressure of O 2 . K responds to temperature through K c and K o , the temperature responses for which are described using a temperature response function described by equation (3) 60 . We thus make the conservative assumption of no direct CO 2 effect on LUE in the C 4 proportion of each pixel. ...
Theory predicts that rising CO2 increases global photosynthesis, a process known as CO2 fertilization, and that this is responsible for much of the current terrestrial carbon sink. The estimated magnitude of the historic CO2 fertilization, however, differs by an order of magnitude between long-term proxies, remote sensing-based estimates and terrestrial biosphere models. Here we constrain the likely historic effect of CO2 on global photosynthesis by combining terrestrial biosphere models, ecological optimality theory, remote sensing approaches and an emergent constraint based on global carbon budget estimates. Our analysis suggests that CO2 fertilization increased global annual terrestrial photosynthesis by 13.5 ± 3.5% or 15.9 ± 2.9 PgC (mean ± s.d.) between 1981 and 2020. Our results help resolve conflicting estimates of the historic sensitivity of global terrestrial photosynthesis to CO2 and highlight the large impact anthropogenic emissions have had on ecosystems worldwide.
... The differential responses of C3 and C4 plants to global change drivers are mainly associated with the essential physiological differences between C3 and C4 photosynthesis. The CO 2 concentrating mechanism in C4 photosynthesis enables a much higher CO 2 partial pressure at the site of Rubisco and consequently a very low (close to nil) photorespiration rate (Hatch, 1987), increasing the photosynthetic efficiency of C4 plants compared with C3 plants at high temperatures and/or low intercellular CO 2 (Ehleringer & Björkman, 1977;Gong et al., 2017;Sage & McKown, 2006). Ehleringer (1978) proposes that temperature is the major factor driving C3/C4 distribution since C4 plants have a higher quantum yield (the ratio of assimilated CO 2 to absorbed photosynthetically active radiation) than C3 plants under high temperatures (Ehleringer & Björkman, 1977). ...
... The CO 2 concentrating mechanism in C4 photosynthesis enables a much higher CO 2 partial pressure at the site of Rubisco and consequently a very low (close to nil) photorespiration rate (Hatch, 1987), increasing the photosynthetic efficiency of C4 plants compared with C3 plants at high temperatures and/or low intercellular CO 2 (Ehleringer & Björkman, 1977;Gong et al., 2017;Sage & McKown, 2006). Ehleringer (1978) proposes that temperature is the major factor driving C3/C4 distribution since C4 plants have a higher quantum yield (the ratio of assimilated CO 2 to absorbed photosynthetically active radiation) than C3 plants under high temperatures (Ehleringer & Björkman, 1977). This mechanism has been termed the quantum yield hypothesis and has been used for predicting distributions of C3 and C4 species at regional to global scales (Collatz et al., 1998;Edwards et al., 2010;Still et al., 2003). ...
Background
C4 plants have increased substantially during the past several decades in the grasslands of the Mongolian Plateau due to regional warming. Here, we explore how the patterns of abundances of C4 annuals and C4 perennials change over space and time.
Methods
A total of 280 sites with C4 plants were surveyed in four types of grasslands in 9 years. The relative biomasses of C4 plants (PC4), C4 annuals (PA4), and C4 perennials (PP4) were calculated. Structural equation modeling was used to analyze the drivers of changes in PA4 and PP4.
Results
At the regional scale, PA4 on average was 11% (±19%, SD) and PP4 was 13% (±19%, SD). Spatially, C4 annuals dominated the C4 communities within an east–west belt region along 44° N and tended to spread toward northern latitudes (about 0.5°) and higher altitudes in the east mountainous areas. The abundance of C4 annuals decreased, while that of C4 perennials increased. The patterns of C4 annuals and C4 perennials were mainly controlled by temperature, growing season precipitation, and dynamics between the two life forms.
Conclusions
C4 annuals exhibited competitive advantages in normal and wet years, while C4 perennials had competitive advantages in dry years. Grazing as a main human disturbance increased C4 annuals, but had no significant effect on C4 perennials.
... Comparatively little work has examined temperature responses of ΦCO2 at light-limiting intensities (e.g. Ehleringer and Björkman, 1977;Ku and Edwards, 1978;Yin et al., 2014) available. This has spawned a LED horticultural lighting industry and the grower is afforded more lighting flexibility and control than ever before. ...
... Surprisingly little work has been reported on the temperature dependence of light-limited ΦCO2 since the work of Ehleringer and Björkman (1977) which limits meaningful comparisons with similar work. It is shown in chapter 5 (Fig. 3) that the temperature response of Amax is quite different to that of ΦCO2. ...
... Tree seedling biomass in the absence of competition or herbivory was increased under eCO 2 (① in Figure 5), as has been found elsewhere for V. karroo and other C 3 savanna tree species (Atkin et al., 1999;Kgope et al., 2010;Wand et al., 1996). This enhanced productivity is primarily due to photosynthetic upregulation (shown by significantly higher V cmax under watered conditions and higher J max under both drought and watered conditions), increased CO 2 availability leading to significantly higher Ci, and higher rates of carbon assimilation due to the elevated CO 2 :O 2 ratio resulting in a higher allocation of Rubisco to carboxylation than to oxygenation (Ehleringer & Björkman, 1977;Ehleringer & Cerling, 2002;Makino & Mae, 1999). High CO 2 availability enabled greater carbon uptake accompanied by relatively low water loss as the need to maintain high gs was reduced (Atkin et al., 1999;Kimball et al., 2002;Morison, 1987). ...
... Although C 4 plants should be at a disadvantage under higher CO 2 conditions, various authors have found C 4 plants to respond to eCO 2 under certain conditions (e.g. Wand et al., 1999) and theory suggests that C 4 plants outperform C 3 plants under high temperatures which are predicted to continue rising globally (Engelbrecht et al., 2015;Pachauri et al., 2014), with C 3 species experiencing greater carboxylation inefficiency when leaf temperatures are high (Ehleringer, 1978;Ehleringer & Björkman, 1977;Yamori et al., 2014). ...
Woody encroachment in southern African savanna has been partly attributed to rising atmospheric [CO2] fertilising the growth of C3 trees but less so that of competing C4 grasses. However, growth conditions (resource availability, competition, rooting space and herbivory) must be suitable for the effects of elevated CO2 (eCO2) to be realised.
This research investigated the interactions between the positive effect of eCO2 on tree seedling growth and limitations imposed by drought, herbivory and competition with C4 grasses. Seedlings of the prolific encroaching C3 tree Vachellia karroo were grown at ambient (400 ppm) or eCO2 (800 ppm) in Open‐Top Chambers and exposed to a variety of stresses typical of savanna systems. Photosynthetic, growth and allocation responses to eCO2 and other treatments were determined.
Unsurprisingly, we show strong growth and water‐saving responses of V. karroo seedlings to eCO2 when in the absence of competition and herbivory. However, the addition of either grass competition or simulated herbivory in the first season of growth significantly moderated this stimulation, while neither drought nor shading diminished the eCO2 effect relative to similarly treated plants grown at ambient [CO2].
Synthesis. We demonstrate that eCO2‐induced C3 stimulation in encroaching savanna species such as V. karroo will be inconsistent across time and space. This research does not detract from the suggestion that increasing atmospheric CO2 is implicated in woody encroachment, but rather that eCO2 benefits to C3 tree seedlings are only realised when growth conditions are suitable. Inconsistencies in eCO2 response will translate into spatial and temporal variation in seedling responses to eCO2 and CO2‐driven woody encroachment, explaining some of the variability observed in woody encroachment across geographical regions and resource and herbivore gradients.
... Given the fact that the sensitivity of A j to CO 2 is much smaller 63 than that of A c , the sensitivity of A j to CO 2 therefore represents a conservative approach to incorporate a CO 2 sensitivity of LUE 39 in remote sensing estimates of photosynthesis. Note that we also make the conservative assumption that C 4 plants operate at or near CO 2 saturation 64 . ...
... where D is vapour pressure deficit, and η ⁎ is the viscosity of water 68 relative to its value at 25 °C, and b is the ratio of the cost of maintaining carboxylation relative to that of maintaining transpiration 66 . The Michaelis-Menten coefficient of RuBisCO (K) is given by: 64 . We thus make the conservative assumption of no direct CO 2 effect on LUE in the C 4 proportion of each pixel. ...
The global terrestrial carbon sink is increasing1,2,3, offsetting roughly a third of anthropogenic CO2 released into the atmosphere each decade¹, and thus serving to slow⁴ the growth of atmospheric CO2. It has been suggested that a CO2-induced long-term increase in global photosynthesis, a process known as CO2 fertilization, is responsible for a large proportion of the current terrestrial carbon sink4,5,6,7. The estimated magnitude of the historic increase in photosynthesis as result of increasing atmospheric CO2 concentrations, however, differs by an order of magnitude between long-term proxies and terrestrial biosphere models7,8,9,10,11,12,13. Here we quantify the historic effect of CO2 on global photosynthesis by identifying an emergent constraint14,15,16 that combines terrestrial biosphere models with global carbon budget estimates. Our analysis suggests that CO2 fertilization increased global annual photosynthesis by 11.85 ± 1.4%, or 13.98 ± 1.63 petagrams carbon (mean ± 95% confidence interval) between 1981 and 2020. Our results help resolve conflicting estimates of the historic sensitivity of global photosynthesis to CO2, and highlight the large impact anthropogenic emissions have had on ecosystems worldwide.
... The course of crop cover development can especially be expected to have changed for crops applying C4 photosynthesis, which respond stronger to temperature changes than crops with C3 photosynthesis. This is due to their stronger increase in quantum yield, which is the ratio of moles CO 2 assimilated to moles of photosynthetically active radiation absorbed (Ehleringer and Björkman, 1977;Still et al., 2003). As a consequence, C4 species increase in growth while C3 remain less affected, which altered the competition between C4 and C3 species and for instance initiated a pronounced expansion of C4 species in the vast C3-C4 mixed grassland in central Asia (Wittmer et al., 2010, Auerswald et al., 2012 even though it had been previously expected that C4 species should profit less than C3 species from the increase in atmospheric CO 2 concentration due to their CO 2 concentrating mechanism (Sage and Kubien, 2003). ...
... Here we could show that climate change induced changes in growing conditions and seasonal distribution of rain erosivity affected the C factors of different crops pronouncedly. For the C3 crops, these changes were mainly caused by the changes in rain erosivity, while growth was affected little, which is in agreement with the comparably low change in quantum yield of C3 plants with temperature (Ehleringer and Björkman, 1977). For maize, the only C4 plant of relevance, additionally a pronounced change in crop development could be shown, which again agrees with predictions from quantum yield but also with other findings based on direct observations or other prediction principles (Stewart et al., 1998;Stone et al., 1999;Olesen et al., 2012). ...
Erosion by water on arable land can be influenced by the farmer mainly by crop selection, cultivation and field management. This requires updated knowledge on the erosion potential of crops, the so-called C factor of the (Revised) Universal Soil Loss Equation. In order to assess how climate change has already altered the C factors, we analysed the effects of a modified crop development and rain erosivity. To this end, we combined more than 4.2 million phenological observations in Germany with the seasonal distribution of rain erosivity derived from contiguous rain radar measurements comprising about 7.7 million events. We then compared the recent C factors to those derived in the 1980s. Due to temperature increase, crops developed earlier and / or faster, which was particularly true for maize due to its C4 mode of photosynthesis; and rains were more erosive during the dormant season. Both had a strong impact on the C factors. In particular, the C factor of maize decreased while that of winter cereals tended to increase because these crops pass the winter period in a stage susceptible to erosion. In consequence, the differences among crops in their erosion potential decreased. Our findings strongly suggest that the winter period has to receive larger attention in soil conservation. Thus, the use of winter cover crops may become even more effective to control erosion.
... As photorespiration is generally small in C 4 plants, measured Φ CO 2 does not differ much between ambient and nonphotorespiratory conditions (e.g. Ehleringer & Björkman, 1977). However, in C 4 plants, especially PEP-CK species where O 2 evolution in the BS compartment can be highest among the three subtypes (Yin & Struik, 2018), there is no guarantee that photorespiration is totally suppressed when using high CO 2 and low O 2 gas mixture. ...
Theoretically, the PEP‐CK C4 subtype has a higher quantum yield of CO2 assimilation (ΦCO2) than NADP‐ME or NAD‐ME subtypes because ATP required for operating the CO2‐concentrating mechanism is believed to mostly come from the mitochondrial electron transport chain (mETC). However, reported ΦCO2 is not higher in PEP‐CK than in the other subtypes. We hypothesise, more photorespiration, associated with higher leakiness and O2 evolution in bundle‐sheath (BS) cells, cancels out energetic advantages in PEP‐CK species.
Nine species (two to four species per subtype) were evaluated by gas exchange, chlorophyll fluorescence, and two‐photon microscopy to estimate the BS conductance (gbs) and leakiness using a biochemical model.
Average gbs estimates were 2.9, 4.8, and 5.0 mmol m⁻² s⁻¹ bar⁻¹, and leakiness values were 0.129, 0.179, and 0.180, in NADP‐ME, NAD‐ME, and PEP‐CK species, respectively. The BS CO2 level was somewhat higher, O2 level was marginally lower, and thus, photorespiratory loss was slightly lower, in NADP‐ME than in NAD‐ME and PEP‐CK species. Differences in these parameters existed among species within a subtype, and gbs was co‐determined by biochemical decarboxylating sites and anatomical characteristics.
Our hypothesis and results partially explain variations in observed ΦCO2, but suggest that PEP‐CK species probably use less ATP from mETC than classically defined PEP‐CK mechanisms.
... Meanwhile, higher temperatures are expected 4 and reported [13][14][15] to favor C 4 over C 3 photosynthesis, because the affinity of O 2 to Rubisco relative to CO 2 becomes stronger with increasing temperature and also due to differing solubilities of CO 2 and O 2 with increasing temperature. This should produce an advantage for the carbon concentrating mechanism of C 4 species, especially under high temperatures 16 . Hence C 4 species are characteristic of tropical and subtropical ecosystems. ...
Plants with the C4 photosynthesis pathway typically respond to climate change differently from more common C3-type plants, due to their distinct anatomical and biochemical characteristics. These different responses are expected to drive changes in global C4 and C3 vegetation distributions. However, current C4 vegetation distribution models may not predict this response as they do not capture multiple interacting factors and often lack observational constraints. Here, we used global observations of plant photosynthetic pathways, satellite remote sensing, and photosynthetic optimality theory to produce an observation-constrained global map of C4 vegetation. We find that global C4 vegetation coverage decreased from 17.7% to 17.1% of the land surface during 2001 to 2019. This was the net result of a reduction in C4 natural grass cover due to elevated CO2 favoring C3-type photosynthesis, and an increase in C4 crop cover, mainly from corn (maize) expansion. Using an emergent constraint approach, we estimated that C4 vegetation contributed 19.5% of global photosynthetic carbon assimilation, a value within the range of previous estimates (18–23%) but higher than the ensemble mean of dynamic global vegetation models (14 ± 13%; mean ± one standard deviation). Our study sheds insight on the critical and underappreciated role of C4 plants in the contemporary global carbon cycle.
... Determinants of the distribution and abundance of C 3 versus C 4 species have been studied for decades, with the relative success of plants that utilize these different photosynthetic pathways usually related to advantages that C 4 species have at warmer temperatures (Teeri and Stowe 1976;Ehleringer and Bjö rkman 1977;Teeri 1979;Pearcy and Ehleringer 1984;Epstein and others 1997;Tieszen and others 1997;Still and others 2003;Yamori and others 2014). Nearly twenty years ago, Winslow and others (2003) proposed the Seasonal Availability of Water (SAW) hypothesis to explain the global distribution of C 3 and C 4 grasses. ...
Understanding how cool-season C3 and warm-season C4 grasses will respond to climate change is critical for predicting future ecosystem functioning in many grasslands. With warming, C4 grasses are expected to increase relative to C3 grasses, but alterations in the seasonal availability of water may also influence C3/C4 dynamics because of their distinct seasons of growth. To better understand how shifts in the seasonal availability of water can affect ecosystem function in a northern mixed-grass prairie in southeastern Wyoming, we reduced early season rainfall (April–June) using rainout shelters and added the amount of excluded precipitation later in the growing season (July–September), effectively shifting spring rainfall to summer rainfall. As expected, this shift in precipitation seasonality altered patterns of soil water availability, leading to a 29% increase in soil respiration and sustained canopy greenness throughout the growing season. Despite these responses, there were no significant differences in C3 aboveground net primary production (ANPP) between the seasonally shifted treatment and the plots that received ambient precipitation, likely due to the high levels of spring soil moisture present before rainout shelters were deployed that sustained C3 grass growth. However, in plots with high C4 grass cover, C4 ANPP increased significantly in response to increased summer rainfall. Overall, we provide the first experimental evidence that shifts in the seasonality of precipitation, with no change in temperature, will differentially impact C3 versus C4 species, altering the dynamics of carbon cycling in this geographically extensive semi-arid grassland.
... Forming grandiose plantations due to its stilted roots, R. apiculata plays an important role in the ecology of mangrove forests (Thongjoo et al. 2018;Wenfang et al. 2020). Of undoubted interest is the fact that R. apiculata belongs to plants with C4 photosynthesis, which allows the plant to better adapt when growing in conditions of high temperatures and lack of water (Ehleringer and Björkman 1977;Slack and Hatch 1967). Therefore, it is not accidental that many researchers pay attention to this species (Christensen 1978;Ong et al. 1995). ...
Mangrove forests are an important part of tropical coastal ecosystems. Until recently, these forests were intensively exterminated. Currently, the issue of mangrove conservation is being discussed at a number of symposiums due to their significant role in reducing the effects of greenhouse gas emissions. However, there has recently been uncertainty in estimation of CO 2 fluxes in mangrove forests due to a lack of field research.
The results of studies of photosynthesis at the leaf level in-situ in seedlings of Rhizophora apiculata Blume, 1827 of both natural and artificial origin are presented. The studies were carried out on a mangrove plantation growing in Can Gio Mangrove Biosphere Reserve, which is 50 kilometres from Ho Chi Minh City (South Vietnam). CO 2 gas exchange during photosynthesis was measured using a gas analysing system called the LI-6800 (USA).
Photosynthetically active radiation (PAR) is the main factor affecting the photosynthesis of the studied seedlings. Artificial seedlings that were grown in open areas had higher productivity and greater photosynthetic rates. It has been determined that the measured photosynthesis are scattered over three clearly marked zones, which correspond to the measurements of photosynthesis made in the pre-noon, noon and afternoon hours. The water reserves used up before noon were not fully replenished in the afternoon by the seedlings. Based on the results obtained, it has been suggested that the main inhibitory factor affecting the photosynthesis of R. apiculata (if PAR is not taken into account) is a violation of the water balance of the leaves.The optimum air temperature for photosynthesis processes in seedlings is (35 ± 2) °C. The intensity of photosynthesis also increases with an increase in the concentration of CO 2 in the air. The increases of photosynthesis continue until the concentration of CO 2 reaches ~1000 µmol·mol ⁻¹ and then do not increase. We associate this circumstance with the maximum possibilities of the photosynthetic apparatus of the leaf of the studied plant.
The obtained research results will contribute to a better theoretical understanding of the productivity of plants of this species in the respective ecosystems, and will also allow us to move from photosynthesis at the leaf level to photosynthesis at the planting level. The work’s mathematical models can be used to model changes in R. apiculata photosynthesis from the point of view of climate change.
... A consensus is that since most C 4 species originated in lower atmospheric CO 2 concentrations 8,9 than currently experienced, C 4 photosynthesis is expected to bene t less from rising CO 2 concentrations than that of C 3 plants. Meanwhile, higher temperature is expected 4 and reported [10][11][12] to favor C 4 photosynthesis over C 3 , because the a nity of O 2 to Rubisco relative to CO 2 becomes stronger with increasing temperature, therefore creating an advantage for C 4 species, which possess a strong carbon concentrating mechanism under high temperature 13 . Hence C 4 species are characteristic of tropical and subtropical ecosystems. ...
Photosynthesis of C 4 plants responds to climate change differently than the more common C 3 plants, due to their unique anatomic and biochemical characteristics. The different response is expected to cause a change in global C 4 distribution, however, current C 4 distribution models are inadequate to predict that as they are based on a temperature-only hypothesis and lack observational constraints. Here, we used a global database of photosynthetic pathways, satellite observations and a photosynthetic optimality theory to produce a new observation-constrained estimate of C 4 distribution. We found that global C 4 coverage stabilized at 11.2% of the vegetated land surface during 1992 to 2016, as a net effect of C 4 grass decrease due to elevated CO 2 and C 4 crop increase, mainly from maize expansion. Using an emergent constraint approach, we estimated that C 4 contributed 12.5% of global photosynthetic carbon assimilation, a value much lower than previous estimates (~ 20%) but more in line with the mean of an ensemble of dynamic global vegetation models (14 ± 13%). By improving the understanding of recent global C 4 dynamics, our study sheds insight on the critical and previously underappreciated role of C 4 plants in modulating the global carbon cycle in recent history.
... The warm-season C 4 grasses of prairie ecosystems are dormant during the winter, with only decadent and senesced materials present aboveground. However, cool-season C 3 species are metabolically active at low temperatures during winter [54]. Consequently, smaller rates and budgets of CO 2 fluxes and ET can be expected during the dormant season for pastures that are not extensively grazed (P18) and receive annual burning. ...
Carbon dioxide (CO2) fluxes and evapotranspiration (ET) during the non-growing season can contribute significantly to the annual carbon and water budgets of agroecosystems. Comparative studies of vegetation phenology and the dynamics of CO2 fluxes and ET during the dormant season of native tallgrass prairies from different landscape positions under the same climatic regime are scarce. Thus, this study compared the dynamics of satellite-derived vegetation phenology (as captured by the enhanced vegetation index (EVI) and the normalized difference vegetation index (NDVI)) and eddy covariance (EC)-measured CO2 fluxes and ET in six differently managed native tallgrass prairie pastures during dormant seasons (November through March). During December–February, vegetation phenology (EVI and NDVI) and the dynamics of eddy fluxes were comparable across all pastures in most years. Large discrepancies in fluxes were observed during March (the time of the initiation of growth of dominant warm-season grasses) across years and pastures due to the influence of weather conditions and management practices. The results illustrated the interactive effects between prescribed spring burns and rainfall on vegetation phenology (i.e., positive and negative impacts of prescribed spring burns under non-drought and drought conditions, respectively). The EVI better tracked the phenology of tallgrass prairie during the dormant season than did NDVI. Similar EVI and NDVI values for the periods when flux magnitudes were different among pastures and years, most likely due to the satellite sensors’ inability to fully observe the presence of some cool-season C3 species under residues, necessitated a multi-level validation approach of using ground-truth observations of species composition, EC measurements, PhenoCam (digital) images, and finer-resolution satellite data to further validate the vegetation phenology derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) during dormant seasons. This study provides novel insights into the dynamics of vegetation phenology, CO2 fluxes, and ET of tallgrass prairie during the dormant season in the U.S. Southern Great Plains.
... The depression of the A n rates in lettuce grown on Pb-rich soil related to the decrease of apparent quantum yield of photosynthesis (α, Table 1), which is defined as the moles of CO 2 fixed per mole of quanta absorbed and reflected the efficiency with, which light, is converted into fixed carbon. This parameter is not a constant and varies depending on the conditions under which photosynthesis occurs [29,40,41]. One of the factors responsible for the change in the α value can be some adjustments in the pigment complex [29], which can be considered as an acclimation process to changes in plant growth conditions [42,43]. ...
Contamination of agricultural soils with heavy metal leads to a decrease in the crop quality and yield, as well as increases in public health risks. In this study, we aimed to evaluate the impact of soil contamination with lead (Pb) on the growth, photosynthesis, respiration, and coupling between these physiological processes, as well as temporal dynamics of Pb uptake and accumulation by lettuce (Lactuca sativa L.) plants. For this 46-day pot experiment, Pb(NO3)2 was mixed with loamy Retisol soil with the rate of 0, 50, and 250 mg kg−1. No significant differences in plant biomass accumulation were found between plants grown on Pb-free and Pb-rich soil, but root-weight ratio, root-to-shoot weight ratio, and leaf area were lower, and the number of leaves and leaf weight per unit area were significantly higher in plants grown on soil contaminated with Pb than in their counterparts grown on Pb-free soil. The concentration of Pb in plant root and shoot followed the increase in soil Pb, with Pb content in the roots being higher than in the shoots. Soil Pb decreased chlorophyll content, net CO2 assimilation rate and photosynthetic light use efficiency, but caused an increase in the leaf respiration rate regardless of whether respiration was performed in the light or in darkness. Increased ratio of respiration to photosynthesis reflects the shift in the carbon balance of lettuce plants toward carbon losses under stress conditions of soil contamination with Pb.
... The maximum quantum yield or Ф(I 0 ) estimated in both studies was very similar, 0.0526 μmol (CO 2 ) μmol −1 (photons) in this study and 0.0518 μmol (CO 2 ) μmol −1 (photons) reported by Baath et al. (2020a), when averaged across growing temperature treatments. In other C3 plants, Ehleringer and Bjorkman (1977) reported similar findings on quantum yield ranging from 0.051-0.055 across seven different species. ...
... The maximum quantum yield or Ф(I 0 ) estimated in both studies was very similar, 0.0526 μmol (CO 2 ) μmol −1 (photons) in this study and 0.0518 μmol (CO 2 ) μmol −1 (photons) reported by Baath et al. (2020a), when averaged across growing temperature treatments. In other C3 plants, Ehleringer and Bjorkman (1977) reported similar findings on quantum yield ranging from 0.051-0.055 across seven different species. ...
Little is known about the photosynthetic physiology of guar
(Cyamopsis tetragonoloba L. Taub), a legume crop, including how
photosynthetic parameters intrinsically vary among germplasm
and their recovery from water stress. To address this, two greenhouse
studies were conducted: Study-1 to compare photosynthetic
light response (AN–I) curves and related parameters in three contrasting
guar genotypes under optimal and post-water deficit conditions;
and Study-2 to quantify photosynthetic parameters in 44
guar genotypes and explore inter-relationships with plant growth
parameters. In Study-1, the mean net photosynthetic rate (AN)
statistically peaked with 1500 μmol (photons) m −2 s −1, though
the maximum AN [33.29 μmol (CO2) m−2 s−1] was modeled to occur
with 1950 μmol (photons) m −2 s −1. The light compensation point
(Icomp), dark respiration rate (RD), and maximum quantum yield
(Ф(I0)) were modeled to be 49.9 μmol (photons) m−2 s−1, 2.62 μmol
(CO2) m−2 s−1, and 0.0526 μmol (CO2) μmol−1 (photons), respectively.
Photosynthesis in guar was resilient to water stress. Despite
reductions in growth, specific leaf area (SLA), and other growth
parameters, persistently drought-stressed guar plants, on average,
exhibited rapid and full recovery of photosynthetic functions when
watered. Genotypes differed in their capacity to recover to some
degree. In Study-2, AN differed only between two of the 44 genotypes
tested, corresponding to the minimum and maximum AN
values. There were no relationships between AN and most plant
growth parameters. This finding suggested there is low potential to
use point measurements of AN as a selection parameter for
increased guar productivity.
... The maximum quantum yield or Ф(I 0 ) estimated in both studies was very similar, 0.0526 μmol (CO 2 ) μmol −1 (photons) in this study and 0.0518 μmol (CO 2 ) μmol −1 (photons) reported by Baath et al. (2020a), when averaged across growing temperature treatments. In other C3 plants, Ehleringer and Bjorkman (1977) reported similar findings on quantum yield ranging from 0.051-0.055 across seven different species. ...
Little is known about the photosynthetic physiology of guar (Cyamopsis tetragonoloba L. Taub), a legume crop, including how photosynthetic parameters intrinsically vary among germplasm and their recovery from water stress. To address this, two greenhouse studies were conducted: Study-1 to compare photosynthetic light response (AN–I) curves and related parameters in three contrasting guar genotypes under optimal and post-water deficit conditions; and Study-2 to quantify photosynthetic parameters in 44 guar genotypes and explore inter-relationships with plant growth parameters. In Study-1, the mean net photosynthetic rate (AN) statistically peaked with 1500 μmol (photons) m ⁻² s ⁻¹, though the maximum AN [33.29 μmol (CO2) m⁻² s⁻¹] was modeled to occur with 1950 μmol (photons) m ⁻² s ⁻¹. The light compensation point (Icomp), dark respiration rate (RD), and maximum quantum yield (Ф(I0)) were modeled to be 49.9 μmol (photons) m⁻² s⁻¹, 2.62 μmol (CO2) m⁻² s⁻¹, and 0.0526 μmol (CO2) μmol⁻¹ (photons), respectively. Photosynthesis in guar was resilient to water stress. Despite reductions in growth, specific leaf area (SLA), and other growth parameters, persistently drought-stressed guar plants, on average, exhibited rapid and full recovery of photosynthetic functions when watered. Genotypes differed in their capacity to recover to some degree. In Study-2, AN differed only between two of the 44 genotypes tested, corresponding to the minimum and maximum AN values. There were no relationships between AN and most plant growth parameters. This finding suggested there is low potential to use point measurements of AN as a selection parameter for increased guar productivity.
... The Farquhar-von Caemmerer-Berry model (Farquhar et al., 1980;von Caemmerer & Farquhar, 1981), hereafter the FvCB model, can model assimilation if the properties and amount of leaf Rubisco, and the photosynthetic electron transport rate, are known. In addition, electron transport rate can be estimated from photosynthesis-irradiance response models (Harbinson & Yin, 2017;Thornley & Johnson, 2000), with the (absolute) light-limited quantum yield and (possibly) leaf light absorption data also being needed to define the lightlimited slope of the light-response curve (Ehleringer & Bjorkman, 1977;Hogewoning et al., 2012). Leaves also function within canopies, which are complex structures within which incident solar irradiance is absorbed, transmitted and scattered, and water vapour and CO 2 move by diffusion and mass transport to and from sites of release and uptake. ...
p>Using the GECROS model, we simulated the effect of improvements in photosynthesis a range of growth parameters, including yield, and on the ε<sub>c</sub> (the conversion efficiency of absorbed solar energy to the chemical energy of biomass) and ε<sub>i</sub> (the efficiency of solar energy interception or absorption by the canopy) parameters of the Monteith crop growth equation, for wheat and potato (which use C3 photosynthesis) and maize (which uses C4 photosynthesis). In the case of the C3 crops, the improvements in photosynthesis were via 20% increases in the parameters V<sub>cmax</sub> (carboxylation capacity of Rubisco), J<sub>max</sub> (electron transport capacity), S<sub>c/o</sub> (Rubisco specificity), κ<sub>2LL</sub> (efficiency of converting incident light into electron transport) and g<sub>m</sub> (mesophyll conductance), while for the C4 crop, it was via 20% increase in V<sub>cmax</sub>, J<sub>max</sub> and S<sub>c/o</sub> and a 20% decrease in g<sub>bs</sub> (the conductance that controls the leak of CO<sub>2</sub> from the bundle sheath cells in C4 leaves). The changes were applied individually and in combination. The responses were modelled using climate data collected over a 10-year period from 66 sites around Europe. Improvements in photosynthesis did result in increases in yield but with considerable variation between the parameters that were adjusted. The greatest increases were obtained for increases in J<sub>max</sub> and κ<sub>2LL</sub> (up to an average 11% increase for total plant biomass), and these increases were found across all Europe. Increases in both these parameters have a predominant effect on the light-use efficiency for subsaturating irradiances. Improvements in the other parameters produced smaller increases.</p
... At strictly lightlimiting irradiances, photosynthetic LUE is maximal; LUE is defined here as the ratio between gross photosynthesis (A gross , μmol m −2 s −1 ) and the absorbed or incident photosynthetic photon flux density (μmol m −2 s −1 ). Maximum, light-limited, photosynthetic efficiency is a complex trait and varies, inter alia, with the wavelengths of light used, photosynthetic metabolism (especially the activity of photorespiration (Ehleringer & Björkman, 1977)), statetransitions the presence of non-photosynthetic pigments (Hogewoning et al., 2012), and photodamage to photosystems I and II (e.g., Kao & Forseth, 1992;Sonoike, 2011). ...
Despite research efforts toward improving crop photosynthetic energy conversion efficiencies over the past 40 years, photosynthetic efficiencies remain far from their theoretical maxima. A major challenge has been that plant photosynthesis is a complex process, controlled by many underlying genetic factors and highly dynamic in response to short‐term environmental changes. Recent approaches to improving photosynthesis involved model‐based identification of the bottlenecks in photosynthesis followed by their genetic modification (GM). While these approaches were successful and inspirational, their dependency on the use of GM techniques may restrict their implementation in some jurisdictions. We therefore suggest greater research focus on a different, yet complementary, approach to improving photosynthetic efficiency: the exploration and exploitation of natural genetic variation in photosynthesis. A substantial improvement in phenotyping and genotyping technology over the past decade has highlighted natural variation in photosynthetic sub‐traits for crop and model species. However, a comprehensive understanding of all the factors responsible for photosynthetic limitations is still lacking. We therefore propose the use of high photosynthetic capacity species as plant models for the exploration of the physiological and genetic basis of high photosynthetic efficiency. While most high photosynthetic capacity species are not suitable as models due to complex genetics and evolutionary distance from crops, we have identified the Brassicaceae species Hirschfeldia incana (L.) Lagr.‐Foss as a promising candidate. In this perspective paper, we describe and advocate the use of H. incana as a complementary model species for the exploration of high maximum CO2 assimilation rates (Pmax) found in some C3 species. We describe the basic biology and evolutionary history of the species and report preliminary leaf gas exchange and biophysics data on its exceptional photosynthetic characteristics. Our data suggests Hirschfeldia incana is an excellent model species for studies aiming at exploiting natural genetic variation in photosynthetic efficiency. Our findings further support the need for further integrated research on high photosynthetic capacity plant species from agriculturally important crop families.
... Agropastoralists often foddered their camelids on maize and other cultigens, and they also released them into crop fields to consume maize stubble after harvest (Popenoe et al., 1989). Amaranth (Amaranthus caudatus) or kiwicha is also a common C 4 plant used to fodder camelids (Beresford--Jones et al., 2011;Brack Egg, 1999;Cadwallader et al., 2012;Ehleringer and Björkman, 1977;Gross et al., 1989). C 3 plants used to fodder camelids include potato (Solanum tuberosum) and quinoa (Chenopodium quinoa). ...
Imperial expansion can have substantial impacts on the daily and long-term activities of colonized regions. However, statecraft can vary depending on local resilience and the decisions made by agropastoralists and other economic collectives. We explore how Wari expansion affected, and was affected by, pastoralists’ activities by examining the isotopic variation of camelid bone, teeth, and hair (or fibres) at three mid-valley (yunga) (500–2300 masl) sites in the Majes and Sihuas valleys of southern Peru. We report stable δ13C and δ15N isotopic compositions (n = 34) of keratin from previously published serial samples of camelid (Lama sp./Vicugna sp.) fibre from the site of Beringa in the Majes Valley, δ13C and δ15N values of bone collagen (n = 6) and δ13C values from tooth enamel bioapatite (n = 65) from Uraca in the Majes Valley, and δ13C and δ15N values of bone collagen (n = 30) from Quilcapampa in the Sihuas Valley. We compare diets between sites and between development phases of individual animals. Extensive networks of inter-valley trails connected neighboring yunga communities and camelid caravans enabled the exchange of goods and ideas. Stable isotope analysis of camelids from these three sites suggests that yunga communities in the Majes and Sihuas valleys were engaged in both highland and coastal camelid-caravan networks prior to Wari expansion that permitted local communities to maintain foddering flexibility. Herders maintained these networks into the Wari era, while also taking advantage of new trading opportunities as they became available.
... Betula pubescens and Hedera helix grown in 35 % [O 2 ] and 300 ppm [CO 2 ] exhibited respective~28 and~35 % increases in stomatal density associated with lower P N and C i (Beerling et al., 1998). The effect of [O 2 ] on P N and R PR is more apparent at low [CO 2 ] (Figs. 2, 5 and 6) due to the high specificity of RubisCO for carboxylation to oxygenation (Ehleringer and Björkman, 1977;Jordan and Ogren, 1984;Tolbert et al., 1995), that can result in a ratio of 100:1 in higher plants (Andrews and Lorimer, 1987). This suggests that the influence of [O 2 ] is likely to have affected stomatal morphology and photosynthetic physiology only during periods characterised by a low CO 2 :O 2 ratio such as the Carboniferous (360 to 300 million years ago) and Plio-Pleistocene (5 million to 12 thousand years ago) (Fig. 1) (Beerling et al., 1998) or reduced seed production/viability (Musgrave and Strain, 1988;André, 2011) when atmospheric [CO 2 ] is high. ...
The atmospheric concentration of carbon dioxide ([CO2]) and oxygen ([O2]) directly influence rates of photosynthesis (PN) and photorespiration (RPR) through the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO). Levels of [CO2] and [O2] have varied over Earth history affecting rates of both CO2 uptake and loss, alongside associated transpirative water-loss. The availability of CO2 has likely acted as a stronger selective pressure than [O2] due to the greater specificity of RubisCO for CO2. The role of [O2], and the interaction of [O2] and [CO2], in plant evolutionary history is less understood. We exposed twelve phylogenetically diverse species to combinations of sub-ambient, ambient and super-ambient [O2] and [CO2] to examine the biochemical and diffusive components of PN and the possible role of [O2] as a selective pressure. Photosynthesis, photosynthetic capacity and stomatal, mesophyll and total conductance to CO2 were higher in the derived eudicot and monocot angiosperms than the more basal ferns, gymnosperms and basal angiosperms which originated in atmospheres characterised by higher CO2:O2 ratios. The ratio of RPR:PN was lower in the monocots, consistent with greater carboxylation capacity and higher stomatal and mesophyll conductance making easier CO2 delivery to chloroplasts. The effect of [O2] and [CO2] on PN/RPR was less evident in more derived species with a higher conductance to CO2. The effect of [O2] was less apparent at high [CO2], suggesting that atmospheric [O2] may only have exerted a strong selective pressure on plant photosynthetic processes during periods characterised by low atmospheric CO2:O2 ratios. Current rising [CO2] will predominantly enhance PN rates in species with low diffusive conductance to CO2.
... Membrane damage is accordingly lower in maize Kumar et al. (2012) Glycine max (C 3 ), Brachiaria brizantha (C 4 ) C 4 species has reduced SOD, CAT and APX activities, while as there is no change in SOD activity and decreased CAT activity in C 3 species, which also has higher membrane damage Vítolo et al. (2012) eCO 2 increases the quantum yield in C 3 species in all the observed temperatures between 10-40°C (Ehleringer & Björkman, 1977). So far as redox biology is concerned, there is a sore lack of studies comparing C 3 and C 4 species for ROS formation or antioxidant capacity under heat stress. ...
Abstract Achieving food security and sustainable food production is a major challenge for plant scientists. To accomplish this, the global food production needs not only to be remarkably boosted, but it has to be achieved under harsh environmental conditions. Moreover, the climate change scenarios estimate an enhanced pressure on crop yields in the upcoming decades. C4 photosynthesis is highly promising to meet these challenges to global food production. Under current CO2 levels, C4 photosynthesis is more efficient than C3 photosynthesis, but more data is needed to map out its response under elevated CO2 (eCO2) conditions. Growing evidence also suggests that C4 photosynthesis could be more efficient in water use under eCO2. Production of reactive oxygen species (ROS) is an inevitable consequence of oxygenic photosynthesis and is also one of the first responses to environmental stresses. C3 and C4 plants have different ROS profiles, mainly because of reduced photorespiration in the latter. Moreover, the effects of eCO2 on C3 and especially C4 plants remain poorly understood. Since C3 and C4 plants have different ROS production patterns, it is likely that ROS signalling and downstream effects on growth and development differ between C3 and C4 plants, which may result in different response to eCO2. This would also be reflected in reproductive success and crop yields. Here we evaluate the recent literature on C3 and C4 plant responses to climate change conditions from the abiotic stress tolerance and food security perspectives, with redox connections. Current body of knowledge suggests engineering C4 photosynthesis into major crops to be a viable way to increase yield, but such attempts have failed because of a lack of basic knowledge in this area. Therefore, this article also aims to fill this gap from the redox perspective.
... The maximum R e -value (9.76 µmol CO 2 m −2 s −1 ) was estimated in this stage might be due to high physiological activities in plants. It is apt to note here that jute is a C3 crop and all values of the parameters were well within the ranges of the C3 crops as reported by Ruimy et al. (1995) and Ehleringer and Björkman (1977). ...
Present study is a maiden attempt to assess net ecosystem exchange (NEE) of carbon dioxide (CO2) fux from jute crop (Corchorus olitorius L.) in the Indo-Gangetic plain by using open-path eddy covariance (EC) technique. Diurnal variations of NEE were strongly infuenced by growth stages of jute crop. Daytime peak NEE varied from−5 µmol m−2 s
−1 (in germination stage) to−23 µmol m−2 s−1 (in fbre development stage). The ecosystem was net CO2 source during nighttime with an average NEE value
of 5–8 μmol m−2 s−1. Combining both daytime and nighttime CO2 fuxes, jute ecosystem was found to be a net CO2 sink on a daily basis except the initial 9 days
from date of sowing. Seasonal and growth stage-wise NEEs were computed, and the seasonal total NEE over the jute season was found to be−268.5 gC m−2 (i.e.
10.3 t CO2 ha-1). In diferent jute growth stages, diurnal variations of NEE were strongly correlated (R2>0.9) with photosynthetic photon fux density (PPFD). Ecosystem level photosynthetic efciency parameters were estimated at each growth stage of
jute crop using the Michaelis–Menten equation. The maximum values of photosynthetic capacity (Pmax, 63.3±1.15 µmol CO2 m−2 s−1) and apparent quantum yield (α, 0.072±0.0045 µmol CO2 µmol photon−1) were observed during the active vegetative stage, and the fbre development stage, respectively. Results of the present study would signifcantly contribute to understanding of the carbon fux from the Indian agroecosystems, which otherwise are very sparse.
... Photosynthesis is a source of primary ecosystem productivity and the most important biological carbon cycle process in terrestrial ecosystems [15,16]. The cultivar Pennisetum purpureum (BRS Capiaçu), similarly to maize (Zeamays sp.), are C4 plants, whose metabolism provides higher CO 2 fixation rates [17,18]. Increased crop productivity is closely related to CO 2 accumulation during the photosynthetic process [19,20]. ...
Due to its high productivity, bovine confinement systems generate high volumes of waste that, when handled poorly, cause numerous environmental problems. One way to avoid such problems is anaerobic biodigestion, an efficient process used in manure treatment, resulting in biogas and biofertilizer as by-products. In this context, this study aimed to evaluate the effects of the application of a biofertilizer originated from the biodigestion of wastewater from dairy cattle activities to produce the forage grass Pennisetum purpureum (elephant grass—BRS Capiaçu). The experiments were carried out in an experimental field belonging to Embrapa—Gado de Leite, located in the municipality of Coronel Pacheco, in the state of Minas Gerais, Brazil, from March to October 2018. Different biofertilizer doses (0, 24, 48 and 72 mm layers) were applied to the elephant grass crop and mean plant height, green and dry mass, productivity, dry matter content, lignin, neutral detergent fibers and acid detergent fibers were determined. Changes in soil fertility at the end of the second cycle after the biofertilizer application were observed. When the biofertilizer was applied at the highest dose, increased forage grass productivity and CO2 fixation were noted, although no significant effect on the assessed nutritional variables was observed.
Graphical Abstract
... The factors controlling the relative abundances of C3/C4 plants especially in the last glacial and now in the Holocene are widely debated (Huang et al., 2001;Liu et al., 2005;Schefuß et al., 2005;Sinninghe Damsté et al., 2011). Modelling studies suggest mean annual temperature, atmospheric pCO 2 , seasonal water availability (distribution of rainfall in the C3 vs C4 growing seasons) or a combination of these determine relative C3/C4 abundances (Ehleringer, 1978;Ehleringer and Björkman, 1977;Ehleringer and Pearcy, 1983;Winslow et al., 2003). A review of relative C3/C4 abundance since the last glacial to Holocene by Rao et al. (2012) seems to indicate that relative C4 abundance increased (temperature-controlled) in the mid-latitudes, whereas relative C4 abundance decreased in the low-latitudes (precipitation-controlled). ...
Peat deposits (>50 ka) in the montane Nilgiris (Western Ghats, India), have been central to the reconstruction of late Quaternary paleoclimate using paleovegetation changes in the forest-grassland vegetation mosaic that coexist here. However, it is well-known that short-term disturbances can also cause vegetation switches when multiple stable vegetation states exist. We studied paleovegetation changes within the alternative stable states framework using stable carbon isotopes (relative abundance of C3-C4 vegetation) on the cellulose fraction from two high-resolution radiocarbon-dated peat cores ~170 m apart in the Sandynallah valley: Core 1 closer to the hillslope (32,000 years old) and Core 2 from the centre of the valley (45,000 years old). Core 1 is located in an ecotone showing shola-sedgeland dynamics with vegetation switching at c.22 ka from shola (possibly due to fire) to a prolonged unstable state until 13 ka sustained by low waterlogging. Following a hiatus c.13 ka, sedgeland dominates, with a shift into shola at 3.75 ka driven by increasing aridity. Core 2 shows a stable sedgeland mixed C3-C4 composition responding to temperature, enriched in C3-vegetation in the last glacial with C4-dominance beginning c.18.5 ka, indicative of deglacial warming. The distinctive vegetation states at corresponding times in Cores 1 and 2 within the same valley, responding independently to disturbances and climate, respectively, is the first paleo-record from an alternative stable states landscape in the montane tropics. Thus, short-term disturbances and site attributes need to be accounted for before ascribing vegetation change to changing climate in such vegetation mosaics.
... Abiotic conditions that favor C 3 or C 4 photosynthesis have previously been framed in terms of the quantum yield, or the net gain of photosynthetic carbon per photon absorbed (Ehleringer and Björkman, 1977;Ehleringer, 1978). This model predicts the geographic distributions of C 3 and C 4 vegetation in the modern Great Plains (Ehleringer, 1978;Ehleringer et al., 1997). ...
Modern physical and chemical soil properties can favor or exclude C3 and C4 plants, yet little is known regarding these relationships from deep-time records that track the evolution and expansion of C4 vegetation. In this study, we used a multi-proxy approach to reconstruct vegetation (C3 vs. C4 biomass) and pedogenic properties (soil alkalinity, salinity, sodicity, and texture) from paleolandscapes at Coffee Ranch, Texas, a site from which fossil horses provide the earliest evidence for C4 herbivory in the Great Plains of North America. Local proportion of C4 biomass was assessed using stable carbon isotope ratios of calcium carbonates (δ¹³Ccc) and organic matter (δ¹³Com) analyzed on four different paleosol types, freshwater tufa, and reworked carbonate nodules in fluvial channel lags. Using a Monte Carlo uncertainty analysis, we interpret δ¹³Ccc (range = −8.5 to −5.2‰ VPDB) and δ¹³Com values (range = −25.9 to −24.2‰ VPDB) to be consistent with C4 biomass low in abundance and variability at the study site, but with large uncertainties that would be overlooked using simple linear mixing model approaches. Paleo-pedogenic properties were reconstructed using pedotransfer functions and provide evidence of possible salinity and sodicity in two of five paleosol profiles. However, saline-sodic conditions and soil texture were not correlated with δ¹³C values, contrary to some modern mixed C3-C4 biomes. Using late Miocene CO2 and paleoclimate model reconstructions, we argue that conditions were at or near crossover thresholds favoring C4 over C3 photosynthesis in the Great Plains despite the low abundance of C4 vegetation across the paleolandscapes. This study presents evidence that abiotic factors that select for C4 plants in modern systems—high growing season temperature, low atmospheric CO2, salinity-sodicity, and soil texture—were less influential in the late Miocene than biotic factors (i.e., ecological feedbacks) that suppressed C4 plants prior to their increase in abundance in the Great Plains in the Pliocene.
... Running C4 photosynthesis gives several advantages to those species employing it. These advantages stem from the ability of C4 photosynthesis to operate efficiently even at lower internal CO2 concentrations (low CO2 compensation point), and from the reduced rate of the Rubisco oxygenation reaction and photorespiration: a) better WUE due to the ability of C4 plants to keep higher carboxylation rates at lower internal CO2 concentration (ci), therefore limiting the need to open stomata during day (Ghannoum, 2009;Ghannoum et al., 2011); b) better NUE due to much lower loss of fixed nitrogen from photorespiration and decreased Rubisco investment in photosynthetic organs (Brown, 1978;Oaks, 1994;Ghannoum et al., 2011), as well as relaxation of selection for a high selectivity for CO2 over O2 that has allowed an increase in Rubisco kcat ; c) increased temperature optimums for photosynthesis, since photorespiration rates rise with temperature Sage and Kubien, 2007); d) improved quantum yield, because the number of photons that need to be absorbed to fix each CO2 molecule is decreased due to the low rate of photorespiration (Ehleringer and Björkman, 1977;Ehleringer and Pearcy, 1983;. ...
In C3 plants, CO2 diffuses into the leaf and is assimilated by the Calvin-Benson cycle in the mesophyll cells. It leaves Rubisco open to its side reaction with O2, resulting in a wasteful cycle known as photorespiration. A sharp fall in atmospheric CO2 levels about 30 million years ago have further increased the side reaction with O2. The pressure to reduce photorespiration led, in over 60 plant genera, to the evolution of a CO2-concentrating mechanism called C4 photosynthesis; in this mode, CO2 is initially incorporated into 4-carbon organic acids, which diffuse to the bundle sheath and are decarboxylated to provide CO2 to Rubisco. Some genera, like Flaveria, contain several species that represent different steps in this complex evolutionary process. However, the majority of terrestrial plant species did not evolve a CO2-concentrating mechanism and perform C3 photosynthesis. This thesis compares photosynthetic metabolism in several species with C3, C4 and intermediate modes of photosynthesis. Metabolite profiling and stable isotope labelling were performed to detect inter-specific differences changes in metabolite profile and, hence, how a pathway operates. The results obtained were subjected to integrative data analyses like hierarchical clustering and principal component analysis, and were deepened by correlation analyses to uncover specific metabolic features and reaction steps that were conserved or differed between species. The main findings are that Calvin-Benson cycle metabolite profiles differ between C3 and C4 species and between different C3 species, including a very different response to rising irradiance in Arabidopsis and rice. These findings confirm Calvin-Benson cycle operation diverged between C3 and C4 species and, most unexpectedly, even between different C3 species. Moreover, primary metabolic profiles supported the current C4 evolutionary model in the genus Flaveria and also provided new insights and opened up new questions. Metabolite profiles also point toward a progressive adjustment of the Calvin-Benson cycle during the evolution of C4 photosynthesis. Overall, this thesis point out the importance of a metabolite-centric approach to uncover underlying differences in species apparently sharing the same photosynthetic routes and as a valid method to investigate evolutionary transition between C3 and C4 photosynthesis.
... This mechanism creates high CO2 concentration in bundle sheath cells suppressing photorespiration by decarboxylating four-carbon acids deriving from mesophyll cells (Taiz & Zeiger, 2010). However, the CO2 concentrating mechanism also makes the quantum yield of C4 plants independent from and temperature (25-30 °C) (Ehleringer & Björkman, 1977), therefore less sensitive to a greenhouse with elevated CO2. In addition, C4 plants cannot either fully exploit the photosynthetic capacity under the temperate Danish climate. ...
Model-based dynamic climate control has enhanced Danish greenhouse energy saving since 2002. Previously, the photosynthetic model of dynamic climate control used general C3 plant parameters for all crop species, which ignored the physiological differences among crops, making it possible to save more energy if modeling accuracy improved. Therefore, this thesis estimated FvCB single-leaf photosynthesis model (Farquhar et al., 1980) and Ball-Berry stomatal conductance model (Ball et al., 1987) parameters for four crop species (Triticum aestivum, Chrysanthemum indicum, Solanum lycopersicum, and Rosa hybrid). Applying the species-dependent parameters archived precise simulation from CO2 in the air entering leaf to its assimilation in the chloroplast. Implement in an actual greenhouse to test energy saving will be conducted in the future.
... Photorespiratory flux must increase with rising temperature to account for increases in the Rubisco oxygenation rate. Thus increased release of previously assimilated CO 2 , a corresponding increase in the CO 2 compensation point and decreased quantum efficiency of photosynthesis resulting in lower net carbon gain for a given amount of photons absorbed are associated with higher temperature (Ehleringer and Björkman, 1977;von Caemmerer, 2000). Plants expressing AP3, which has previously shown enhanced performance under high photorespiratory stress (South et al., 2019), also demonstrated enhanced thermal protection ( Figure 2) and higher rates of leaf photosynthesis above 35°C (Figures 2 and 3a). ...
Adapting crops to warmer growing season temperatures is a major challenge in mitigating the impacts of climate change on crop production. Warming temperatures drive greater evaporative demand and can directly interfere with both reproductive and vegetative physiological processes. Most of the world’s crop species have C3 photosynthetic metabolism for which increasing temperature means higher rates of photorespiration, wherein the enzyme responsible for fixing CO2 fixes O2 instead followed by an energetically costly recycling pathway that spans several cell compartments. In C3 crops like wheat, rice and soybean, photorespiration translates into large yield losses that are predicted to increase as global temperature warms. Engineering less energy‐intensive alternative photorespiratory pathways into crop chloroplasts drives increases in C3 biomass production under agricultural field conditions, but the efficacy of these pathways in mitigating the impact of warmer growing temperatures has not been tested. We grew tobacco plants expressing an alternative photorespiratory pathway under current and elevated temperatures (+5°C) in agricultural field conditions. Engineered plants exhibited higher photosynthetic quantum efficiency under heated conditions than the control plants, and produced 26% (between 16‐37%) more total biomass than WT plants under heated conditions, compared to 11% (between 5‐17%) under ambient conditions. That is, engineered plants sustained 15% (between 11 – 21%) less yield loss under heated conditions compared to non‐engineered plants. These results support the theoretical predictions of temperature impacts on photorespiratory losses and provide insight toward the optimization strategies required to help sustain or improve C3 crop yields in a warming climate.
... The light intensity was changed in a stepwise manner to 200, 150, 100, and 50 μmol m -2 s -1 , and. after waiting 1.5 min at each light intensity, the data were recorded. The apparent quantum yield of photosynthesis (AQY) was estimated as the slope of the linear relationship between P n and light intensity under low light (50-200 μmol m -2 s -1 ; Ehleringer and Björkman, 1977). ...
Whether photosynthesis has improved with increasing yield in major crops remains controversial. Research in this area has often neglected to account for differences in light intensity experienced by cultivars released in different years. Light intensity is expected to be positively associated with photosynthetic capacity and resistance of the photosynthetic apparatus to high light but negatively associated with light utilization efficiency under low light. Here, we analyzed the light environment, photosynthetic activity, and protein components of leaves of 26 winter wheat cultivars released during the past 60 years in China. Over time, light levels on flag leaves significantly decreased due to architectural changes, but photosynthetic rates under high or low light and the resistance of the photosynthetic apparatus to high light remained steady, contrary to expectations. We propose that the difference between the actual and expected trends is due to breeding. Specifically, breeding has optimized photosynthetic performance under high light rather than low light. Moreover, breeding selectivity altered the stoichiometry of several proteins related to dynamic photosynthesis, canopy light distribution, and photoprotection. These results indicate that breeding has significantly altered the photosynthetic mechanism in wheat and its response to the light environment. These changes likely have helped increase wheat yields.
... At present, the major patterns in the ecology and evolution of C 3 and C 4 plants are attributed to the physiological differences between the C 3 and C 4 photosynthetic pathways. The foundation for this theory is the observation that the two pathways translate into distinct physiological advantages and disadvantages under different environmental conditions (Berry 1975;Ehleringer and Björkman 1977). C 3 photosynthesis provides advantages over C 4 photosynthesis under low light intensities, high carbon dioxide levels, and cool temperatures, while C 4 photosynthesis provides advantages over C 3 photosynthesis under high light intensities, low carbon dioxide levels, and warm temperatures (Berry and Björkman 1980;Berry and Downton 1982;Pearcy and Ehleringer 1984). ...
Here, we describe a model of C 3 , C 3 –C 4 intermediate, and C 4 photosynthesis that is designed to facilitate quantitative analysis of physiological measurements. The model relates the factors limiting electron transport and carbon metabolism, the regulatory processes that coordinate these metabolic domains, and the responses to light, carbon dioxide, and temperature. It has three unique features. First, mechanistic expressions describe how the cytochrome b 6 f complex controls electron transport in mesophyll and bundle sheath chloroplasts. Second, the coupling between the mesophyll and bundle sheath expressions represents how feedback regulation of Cyt b 6 f coordinates electron transport and carbon metabolism. Third, the temperature sensitivity of Cyt b 6 f is differentiated from that of the coupling between NADPH, Fd, and ATP production. Using this model, we present simulations demonstrating that the light dependence of the carbon dioxide compensation point in C 3 –C 4 leaves can be explained by co-occurrence of light saturation in the mesophyll and light limitation in the bundle sheath. We also present inversions demonstrating that population-level variation in the carbon dioxide compensation point in a Type I C 3 –C 4 plant, Flaveria chloraefolia , can be explained by variable allocation of photosynthetic capacity to the bundle sheath. These results suggest that Type I C 3 –C 4 intermediate plants adjust pigment and protein distributions to optimize the glycine shuttle under different light and temperature regimes, and that the malate and aspartate shuttles may have originally functioned to smooth out the energy supply and demand associated with the glycine shuttle. This model has a wide range of potential applications to physiological, ecological, and evolutionary questions.
... Photosynthetic capacity parameters differed between mango cultivars studied depending on the elevation. Cultivar Tainong No. 1 had a higher Vmax, Jmax, AQYmoles of CO2 fixed per mole photons (Ehleringer and Björkman 1977, Ehleringer and Pearcy 1983, Oberhuber et al. 1993, and PNmax at 1,050 m, while this was true for Jinhuang at 450 m. Similar studies on tropical plant species have also reported higher Vmax, Jmax, AQY, and PNmax at a higher elevation (Laisk et al. 1997, Shi et al. 2006, Fujimura et al. 2010, Liu et al. 2012, Dusenge et al. 2015. ...
Anticipating warming related to climate change, commercial mango plantations in China have been shifting from lower to higher elevations. Such a practice may expose mangoes to climatic conditions that could affect photosynthesis. Photosynthesis research on mango has previously examined mature plantations but exploring adequate functions before the time of fruit production is necessary for later crop success. Therefore, we established two main commercial mango cultivars, Tainong No. 1 and Jinhuang, at 450 m and 1,050 m and examined their photosynthetic performance. Our results showed that photosynthetic capacity parameters, including maximum photosynthetic rate, apparent quantum yield, maximum carboxylation rate, and photosynthetic electron transport rate, were significantly different between cultivars due to elevation and positively correlated with leaf nitrogen per area. Moreover, the seasonal gas exchange of the two cultivars showed variations due to elevation, particularly during the warmer seasons. Therefore, elevation affects the photosynthetic performance of these mango cultivars.
... Each of these tundra PFTs was assigned values of required model parameters (Table 2.2) based on available physiological information [see e.g. Berry and Björkman, 1980;Berry and Downton, 1982;Ehleringer and Björkman, 1977;Farquhar and von Caemmerer, 1982;Kirschbaum and Farquhar, 1984;Körner, 1999;Larcher, 1995] with supplementary limits inferred by comparison of species distributions with climate data. These tundra PFTs use the C 3 photosynthetic pathway and are shallow rooting, and suceptible to water stress and fire. ...
... The parameter is the moles of CO 2 fixed per mole of quanta absorbed; respectively, it defines the efficiency of light utilization in photosynthesis. The quantum yield has some important implications, since it defines plant productivity under limited light, considering that under natural conditions the photosynthetic rate is limited by light most of the time (Ehleringer and Björkman 1977). The DW cycle resulted in reduced α (Table 6), with the inhibitory effect of low soil water availability on α greater for 0S and 10S (35% (P = 0.029) and 42% (P = 0.019), respectively) than for 5S (19% (P = 0.355)) (Fig. 4a). ...
The application of carbon-rich substrates to agricultural soils is discussed as a strategy to improve soil properties and fertility, which can affect plant physiological traits and enhance agricultural crop yield. The aim of this study was to evaluate if shungite, carbon-rich sedimentary-volcanic rock, may improve plant ecophysiological traits under sufficient water supply as well as soil water deficit. A pot culture experiment was conducted with onion (Allium cepa L.) seedlings, using four shungite concentrations (0, 5, 10 and 20 g kg−1) in an Umbric Podzols and two water regimes: well-watered and drying-wetting cycles. Soil water deficit decreased root nutrient content, depressed seedlings growth, net CO2 assimilation rate (An), stomatal conductance (gs) and the respiration rates in both darkness (Rd) and the light (Rl), but increased water use efficiency (WUE) at leaf level. Shungite application decreased the leaf necrosis under both water regimes and increased total leaf length of DW seedlings. Compared with the well-watered conditions, under drying-wetting cycle shungite stimulated the increase of the An rate and WUE at low measurement temperature. No significant effect of shungite was found for Rd, Rl, Rl/Rd, Rd/Ag (Ag = An + Rl) and Rl/Ag regardless soil water regimes. Shungite application was not so successful to eliminate the negative effects of soil water deficit on growth and physiological processes of A. cepa. The observed positive effects of shungite on the physiological traits of onion seedlings were more likely associated with the increase in the content of nutrients than with the improvement in soil water properties.
... Siwalik data from Karp et al. (2018) and Bengal Fan data from this study are normalized to their maximum values to facilitate comparison. conditions (Ehleringer & Björkman, 1977;Ehleringer, 1978Ehleringer, , 2005. A decrease in atmospheric CO 2 levels before or during the late Miocene was likely necessary to facilitate the widespread emergence of open C 4 ecosystems, but not sufficient to account for differences in timing or the speed at which the transition took place across the globe (Edwards et al., 2010;Fox et al., 2018;Pagani et al., 1999;Polissar et al., 2019;Zhou et al., 2018). ...
Fire dynamics potentially account for the asynchronous timing of the expansion of C4 grasslands throughout the Mio‐Pliocene world. Yet how fire, climate, and ecosystems interacted in different settings remain poorly constrained because it is difficult to quantify fires and fuel source over these timescales. Here, we apply molecular proxies for fire occurrence alongside records of vegetation change and paleohydrology in Bengal Fan sediments (ODP Leg 116) to examine fire feedbacks on the south Asian continent. We employ abundances of polycyclic aromatic hydrocarbons (PAHs) to reconstruct fire occurrence and δ¹³C measurements of pyrogenic PAHs to constrain fuel source and grassland burning. This combination allowed us to test whether: (1) a fire‐seasonality forcing facilitated the expansion of grassland ecosystems and (2) a fire‐C4 grass burning feedback maintained these systems. PAHs can be sourced from weathered fossil carbon (i.e., a petrogenic source) and from burned terrestrial biomass (i.e., a pyrogenic source). Alkylated and non‐alkylated structure abundance data distinguished pyrogenic from petrogenic sourced samples. A sharp increase in pyrogenic PAHs along with increases in δ²H and δ¹³C values of plant waxes at 7.4 Ma indicates increased fire coincided with the onset of C4 expansion and hydrologic change in South Asia. The correlated ¹³C enrichment in PAHs, ¹³C enrichment in plant waxes, and increased abundances of PAHs suggest burning of C4 grasslands likely maintained open ecosystems. Our results link fire to the initial opening of grassland ecosystems on a subcontinental‐scale and support disturbance as a critical mechanism of terrestrial biome transition.
Climate change exerts multiple impacts on water-induced soil erosion. Regarding the change in annual rainfall erosivity, the picture is clearest. Despite a small potential increase in mean temperature, a substantial increase in annual rainfall erosivity is generally expected in a warmer world. Data from Ger-many show that annual erosivity has approximately doubled within the last 60 years. Regarding the seasonality of soil cover by different crops, the influence of climate change is more diverse. Changes in sowing and harvesting dates can lead to more or to less soil protection, while an expansion of warm-season crops, in particular C4 row crops like maize, generally reduce soil protection. Wildfires and irrigation may additionally increase erosion. Overall, more water erosion can be expected in many regions. Implementing soil conservation to safeguard the world's soils and their ability to store water becomes even more important as climate change amplifies the variability of precipitation.
The photosynthetic quantum efficiency (φ_0) is a key input parameter for modelling gross primary productivity in terrestrial biosphere models. Historically, these models assumed φ_0 to be constant, based on leaf measurements under unstressed conditions and within a narrow temperature range. However, increasing evidence suggests a temperature-dependent φ_0 on temperature, though it remains unclear whether this response is generalized or if it propagates to the ecosystem. Here, we derived φ_0 (T) at the ecosystem level for sites distributed globally, using sub-daily eddy covariance measurements of CO2 exchange and above/below-canopy measurements of photosynthetic flux density to derive the fraction of absorbed photosynthetically active radiation (fAPAR). We found that φ_0 (T) shows a consistent bell-shaped response curve with temperature in all the sites we analysed. These patterns held when analysed with a larger global dataset using remotely sensed fAPAR. Furthermore, we observed that the values of φ_0 (T) are not markedly different among biomes, instead, there is a gradual transition of the peak φ_0 (T) which decreases following an aridity gradient. Additionally, we noted varying sensitivity to temperature among the different sites, with sensitivity increasing as growth temperature decreases.
C₄ is one of three known photosynthetic processes of carbon fixation in flowering plants. It evolved independently more than 61 times in multiple angiosperm lineages and consists of a series of anatomical and biochemical modifications to the ancestral C3 pathway increasing plant productivity under warm and light‐rich conditions. The C4 lineages of eudicots belong to seven orders and 15 families, are phylogenetically less constrained than those of monocots and entail an enormous structural and ecological diversity. Eudicot C4 lineages likely evolved the C4 syndrome along different evolutionary paths. Therefore, a better understanding of this diversity is key to understanding the evolution of this complex trait as a whole. By compiling 1207 recognised C4 eudicots species described in the literature and presenting trait data among these species, we identify global centres of species richness and of high phylogenetic diversity. Furthermore, we discuss climatic preferences in the context of plant functional traits. We identify two hotspots of C4 eudicot diversity: arid regions of Mexico/Southern United States and Australia, which show a similarly high number of different C4 eudicot genera but differ in the number of C4 lineages that evolved in situ. Further eudicot C4 hotspots with many different families and genera are in South Africa, West Africa, Patagonia, Central Asia and the Mediterranean. In general, C4 eudicots are diverse in deserts and xeric shrublands, tropical and subtropical grasslands, savannas and shrublands. We found C4 eudicots to occur in areas with less annual precipitation than C4 grasses which can be explained by frequently associated adaptations to drought stress such as among others succulence and salt tolerance. The data indicate that C4 eudicot lineages utilising the NAD‐ME decarboxylating enzyme grow in drier areas than those using the NADP‐ME decarboxylating enzyme indicating biochemical restrictions of the later system in higher temperatures. We conclude that in most eudicot lineages, C4 evolved in ancestrally already drought‐adapted clades and enabled these to further spread in these habitats and colonise even drier areas.
Root-derived inorganic carbon has been demonstrated to contribute to plant carbon gain by many experiments in the laboratory. However, it remains largely unknown whether and to what extent soil dissolved inorganic carbon (DIC) influences leaf photosynthesis in karst environments. In this chapter, we first review the current knowledge regarding the uptake, transport, allocation, and assimilation of DIC in plant organs and revisit several representative reports concerning the bicarbonate assimilation by plants under simulated karst environments. Then we summarize the characteristics of natural karst enviroments and provide theoretical models to quantify the contribution of soil DIC to leaf total photosynthesis in field conditions. Further, isotope evidence for plants’ use of soil DIC in karst habitas and species-specific induced variation in DIC assimilation as well as their spatial–temporal heterogeneity are discussed. Finally, we highlight ecophysiological and biogeochemical significance of DIC assimilation in the karst environments, for instance the possible strategy for plants adapting to karst environments and the impact on the estimation of global carbon budget.KeywordsDissolved inorganic carbonRoot uptakeTranspiration streamLeaf photosynthesisKarstIsotopePhotosynthetic modelCarbon sink
Background:
Numerous groups of plants have adapted to CO2 limitations by independently evolving C4 photosynthesis. This trait relies on concerted changes in anatomy and biochemistry to concentrate CO2 within the leaf and thereby boost productivity in tropical conditions. The ecological and economical importance of C4 photosynthesis has motivated intense research, often relying on comparisons between distantly related C4 and non-C4 plants. The photosynthetic type is fixed in most species, with the notable exception of the grass Alloteropsis semialata. This species includes populations exhibiting the ancestral C3 state in southern Africa, intermediate populations in the Zambezian region and C4 populations spread around the paleotropics.
Scope:
We compile here the knowledge on the distribution and evolutionary history of the Alloteropsis genus as a whole and discuss how this has furthered our understanding of C4 evolution. We then present a chromosome-level reference genome for a C3 individual and compare the genomic architecture to that of a C4 accession of A. semialata.
Conclusions:
Alloteropsis semialata represents one of the best systems to investigate the evolution of C4 photosynthesis as the genetic and phenotypic variation provides a fertile ground for comparative and population-level studies. Preliminary comparative genomic investigations show the C3 and C4 genomes are highly syntenic, and have undergone a modest amount of gene duplication and translocation since the different photosynthetic groups diverged. The background knowledge and publicly available genomic resources make Alloteropsis semialata a great model for further comparative analyses of photosynthetic diversification.
C4 photosynthesis results from anatomical and biochemical characteristics that together concentrate CO2 around ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), increasing productivity in warm conditions. This complex trait evolved through the gradual accumulation of components, and particular species possess only some of these, resulting in weak C4 activity. The consequences of adding C4 components have been modelled and investigated through comparative approaches, but the intraspecific dynamics responsible for strengthening the C4 pathway remain largely unexplored. Here, we evaluate the link between anatomical variation and C4 activity, focusing on populations of the photosynthetically diverse grass Alloteropsis semialata that fix various proportions of carbon via the C4 cycle. The carbon isotope ratios in these populations range from values typical of C3 to those typical of C4 plants. This variation is statistically explained by a combination of leaf anatomical traits linked to the preponderance of bundle sheath tissue. We hypothesize that increased investment in bundle sheath boosts the strength of the intercellular C4 pump and shifts the balance of carbon acquisition towards the C4 cycle. Carbon isotope ratios indicating a stronger C4 pathway are associated with warmer, drier environments, suggesting that incremental anatomical alterations can lead to the emergence of C4 physiology during local adaptation within metapopulations.
The quantum yield of photosynthesis (QY, CO2 fixed per light absorbed) depends on the efficiency of light absorption, the coupling between light absorption and electron transport, and the coupling between electron transport and carbon metabolism. QY is generally lower in C3 relative to C4 plants at warm temperatures and differs among the C4 subtypes. We investigated the acclimation to shade of light absorption and electron transport in six representative grasses with C3 , C3 -C4 and C4 photosynthesis. Plants were grown under full (control) or 25% (shade) sunlight. We measured the in vivo activity and stoichiometry of PSI and PSII, leaf spectral properties and pigment contents, and photosynthetic enzyme activities. Under control growth-light conditions, C4 species had higher CO2 assimilation rates, which declined to a greater extent relative to the C3 species. Whole leaf PSII/PSI ratios were highest in the C3 species, while QY and cyclic electron flow (CEF) were highest in the C4 , NADP-ME species. Shade significantly reduced leaf PSII/PSI, linear electron flow (LEF) and CEF of most species. Overall, shade reduced leaf absorptance, especially in the green region, as well as carotenoid and chlorophyll contents in C4 more than non-C4 species. The NAD-ME species underwent the greatest reduction in leaf absorptance and pigments under shade. In conclusion, shade compromised QY the least in the C3 and the most in the C4 -NAD-ME species. Different sensitivity to shade was associated with the ability to maintain leaf absorptance and pigments. This is important for maximising light absorption and minimising photoprotection under low light. This article is protected by copyright. All rights reserved.
The conservation status of large-bodied mammals is dire. Their decline has serious consequences because they have unique ecological roles not replicated by smaller-bodied animals. Here, we use the fossil record of the megafauna extinction at the terminal Pleistocene to explore the consequences of past biodiversity loss. We characterize the isotopic and body-size niche of a mammal community in Texas before and after the event to assess the influence on the ecology and ecological interactions of surviving species (>1 kg). Preextinction, a variety of C4 grazers, C3 browsers, and mixed feeders existed, similar to modern African savannas, with likely specialization among the two sabertooth species for juvenile grazers. Postextinction, body size and isotopic niche space were lost, and the δ13C and δ15N values of some survivors shifted. We see mesocarnivore release within the Felidae: the jaguar, now an apex carnivore, moved into the specialized isotopic niche previously occupied by extinct cats. Puma, previously absent, became common and lynx shifted toward consuming more C4-based resources. Lagomorphs were the only herbivores to shift toward C4 resources. Body size changes from the Pleistocene to Holocene were species-specific, with some animals (deer, hare) becoming significantly larger and others smaller (bison, rabbits) or exhibiting no change to climate shifts or biodiversity loss. Overall, the Holocene body-size-isotopic niche was drastically reduced and considerable ecological complexity lost. We conclude biodiversity loss led to reorganization of survivors and many "missing pieces" within our community; without intervention, the loss of Earth's remaining ecosystems that support megafauna will likely suffer the same fate.
Although greenhouse agriculture can generate high crop yields, they vary due to spatiotemporal differences in incident light and photosynthesis. To elucidate these dynamics, multipoint analysis of hemispheric images and a photosynthesis model were used to visualize the spatiotemporal distribution of photosynthetic photon flux density (PPFD) and leaf photosynthetic rate (A) and compared these with strawberry fruit yield in a greenhouse. This method enabled successful estimation of spatiotemporal variability in PPFD and A with relative root mean square errors of 4.4% and 11.0%, respectively. PPFD, captured at ca. 2 m resolution, varied diurnally and seasonally based on sun position and external light intensity. A showed less spatial variability, because it is reduced by physical and physiological mechanisms in the leaves at excessive leaf temperatures and becomes saturated at high PPFD. Yield spatial variability was better explained by A than by PPFD. The association between A and yield weakened over the cultivation period (R² declined from 46% in winter to 12% in spring), thus suggesting that, over the cultivation period, factors such as photoassimilate availability replaced A as the primary limiting factor. The proposed method can be directly applied to other types of greenhouses, and the findings may facilitate spatiotemporal optimization in crop production, improving precision greenhouse agriculture.
Accurate mapping of coarse cereals envisaged maize to be discriminated from co-existing Kharif crops using multiplatform, multiparametric SAR and Optical data in various polarization combination from Sentinel-1 and RADARSAT-2 in synergism with Sentinel-2, under machine learning algorithms viz. support vector machine (SVM) and random forest (RF) and knowledge-based Decision Tree (DT). SVM over-estimates the area of maize whereas RF and DT performed similarly (60–75%) but DT being closest to field conditions (68–78%). A 4 date Sentinel-1 under DT classified Soybean to 62% accuracy and Cotton to 76% on a regional scale in Maharashtra. Inclusion of 1-date optical image improved sugarcane accuracy. The similar-structured crops, such as Maize and Pearl Millet were discriminated with their unique phenological response in crop-calendar using quad-pol RADARSAT-2. With inclusion of crop responsive model-based polarimetric decomposition (Yamaguchi Volume and Double-Bounce) and Eigen-based parameters (Entropy and Alpha-Angle), maize classification accuracy elevated to 84%.
d-Ribulose-1,5-di-P carboxylase, purified from soybeans, had Km values of 0.13 mm for CO2 and 0.19 mm for ribulose-1,5-di-P under a N2 atmosphere. O2 inhibited ¹⁴CO2 incorporation by the enzyme and this inhibition was rapidly reversed by N2. Inhibition was competitive with respect to CO2 and uncompetitive with respect to ribulose-1,5-di-P. The Ki for O2 was 0.8 mm. This O2 inhibition, together with the ribulose-1,5-di-P carboxylase-catalyzed oxidation of ribulose-1,5-di-P to P-glycolate observed previously (Bowes, G., Ogren, W. L., and Hageman, R. H. (1971) Biochem. Biophys. Res. Commun. 45, 716–722), explains the “Warburg effect”: the rapidly reversible O2 inhibition of photosynthesis and stimulation of glycolate production seen in plants and isolated chloroplasts. In corn and soybean extracts, ribulose-1,5-di-P carboxylase was inhibited by O2 but P-enolpyruvate carboxylase was unaffected. These data may explain the different response to O2 by plants which utilize ribulose-1,5-di-P carboxylase for the initial photosynthetic carboxylation and those utilizing P-enolpyruvate carboxylase. The optimum temperature for purified ribulose-1,5-di-P carboxylase was 55° and activation energies, in kilocalories per mole, were 18.4 in N2 and 20.4 in O2.
Phosphorylated compounds inhibited ¹⁴CO2 incorporation by the enzyme. Nonphosphorylated sugars, including ribulose, did not inhibit. Fructose-1,6-di-P was a competitive inhibitor with respect to ribulose-1,5-di-P, the Ki being 0.88 mm. Fructose-1,6-di-P was a more effective inhibitor than fructose-6-P, fructose-1-P, and ribulose-5-P suggesting that both phosphate groups of ribulose-1,5-di-P are involved in binding to the enzyme. HgCl2 was a noncompetitive inhibitor with respect to CO2 and a mixed inhibitor with respect to ribulose-1,5-di-P, suggesting that sulfhydryl groups are not involved in CO2 binding but may be close to the site where ribulose-1,5-di-P binds to the enzyme.
1. Radioactive products in detached leaf segments were examined after periods of steady-state photosynthesis in (14)CO(2). 2. After exposure to (14)CO(2) for approx. 1sec. more than 93% of the fixed radioactivity was located in malate, aspartate and oxaloacetate. After longer periods large proportions of the radioactivity appeared in 3-phosphoglycerate, hexose monophosphates and sucrose. Similar results were obtained with leaves still attached to the plant. 3. Radioactivity appeared first in C-4 of the dicarboxylic acids and C-1 of 3-phosphoglycerate. The labelling pattern in hexoses was consistent with their formation from 3-phosphoglycerate. 4. The reaction giving rise to C(4) dicarboxylic acid appears to be the only quantitatively significant carboxylation reaction. 5. Evidence is provided that the radioactivity incorporated into the C(4) dicarboxylic acid pool is transferred to sugars via 3-phosphoglycerate. A scheme is proposed to account for these observations.
It is certainly a pleasure, and a privilege to be invited to this meeting on Environmental Control of Photosynthesis, a topic that lies very close to my heart. Regardless of what our individual motivations for working in this particular field of research may be I am sure that all of the members of the audience agree that this is indeed a very important field for many reasons.
The rate of sugar formation from aspartate-14C(U) and alanine-L-14C was examined under various light intensities in three C4-plants. The results obtained were as follows.
Kinetic properties of soybean net photosynthetic CO(2) fixation and of the carboxylase and oxygenase activities of purified soybean (Glycine max [L.] Merr.) ribulose 1, 5-diphosphate carboxylase (EC 4.1.1.39) were examined as functions of temperature, CO(2) concentration, and O(2) concentration. With leaves, O(2) inhibition of net photosynthetic CO(2) fixation increased when the ambient leaf temperature was increased. The increased inhibition of CO(2) fixation at higher temperatures was caused by a reduced affinity of the leaf for CO(2) and an increased affinity of the leaf for O(2). With purified ribulose 1,5-diphosphate carboxylase, O(2) inhibition of CO(2) incorporation and the ratio of oxygenase activity to carboxylase activity increased with increased temperature. The increased O(2) sensitivity of the enzyme at higher temperature was caused by a reduced affinity of the enzyme for CO(2) and a slightly increased affinity of the enzyme for O(2). The similarity of the effect of temperature on the affinity of intact leaves and of ribulose 1,5-diphosphate carboxylase for CO(2) and O(2) provides further evidence that the carboxylase regulates the O(2) response of photosynthetic CO(2) fixation in soybean leaves. Based on results reported here and in the literature, a scheme outlining the stoichiometry between CO(2) and O(2) fixation in vivo is proposed.Oxygen competitively inhibited carboxylase activity with respect to CO(2), and CO(2) competitively inhibited oxygenase activity with respect to O(2). Within the limits of experimental error, the Michaelis constant (CO(2)) in the carboxylase reaction was identical with the inhibition constant (CO(2)) in the oxygenase reaction, and the Michaelis constant (O(2)) in the oxygenase reaction was identical with the inhibition constant (O(2)) in the carboxylase reaction. The Michaelis constant, (ribulose 1,5-diphosphate) was the same in both the carboxylase and oxygenase reactions. This equality of kinetic constants is consistent with the notion that the same enzyme catalyzes both reactions.
The efficiency of photosynthetic utilization of light in Calvin cycle plants was lower than that found in plants with the C 4 ‐dicarboxylic acid path of CO 2 fixation when measured in air. Inhibition of photorespiration by O 2 depletion indicated that potential photosynthetic efficiencies of both groups were similar. The ability of C 4 plants to utilize higher light intensities than Calvin cycle plants was associated with a greater affinity for CO 2 at the carboxylation site.
Photorespiration was detected in a leaf attached to an 18 month old sugarcane plant. The leaf was significantly less efficient than similar leaves from a young plant and displayed a greater resistance to CO 2 transport. An explanation is advanced in terms of end‐product feedback from assimilate stored in the stalk.
A closed gas exchange system was used to survey the apparent rates of photosynthesis by young wheat shoots in a wide range of O2 concentrations (O2), CO2 concentrations (CO2), temperatures (T), and radiant flux densities. The results are expressed graphically and by equations. The carbon dioxide compensation point (ΓH) conformed to the equation ΓH = O2e(0.0428T − 12.1). The relationship between the apparent rates of photosynthesis in the presence (PH) and absence (PL) of inhibitory concentrations of oxygen was described by the equation PH = PLk loge(CO2/ΓH) where k was independent of the prevailing environmental conditions and .
The influence of oxygen concentration in the range 0–21% on photosynthesis in intact leaves of a number of higher plants has been investigated.
Photosynthetic Co 2 fixation of higher plants is markedly inhibited by oxygen in concentrations down to less than 2%. The inhibition increases with oxygen concentration and is about 30% in an atmosphere of 21% O 2 and 0.03% Co. 2 . Undoubtedly, therefore, oxygen in normal air exerts a strong inhibitory effect on photosynthetic Co 2 fixation of land plants under natural conditions.
The inhibitory effect of oxygen is rapidly produced and fully reversible.
The degree of inhibition is independent of light intensity.
The quantum yield for Co 2 fixation, i.e . the slope of the linear part of the curve for Co 2 uptake versus absorbed quanta, is inhibited to the same degree as the light saturated rate at all oxygen concentrations studied.
Diverse species of higher plants, varying greatly in photosynthetic response to light intensity and Co 2 concentration, and with light saturated roles of Co 2 fixation differing by a factor of more than 10 times, show a remarkable similarity in their response to oxygen concentration. By contrast, when studied under the same conditions as the higher plants, the green algae Chlorella and Ulva did not show‐any measurable inhibition of photosynthetic Co 2 fixation. Similarity, the increase in fluorescence intensity with increasing oxygen concentrations found in higher plants also was not seen in Chlorella . The present results, together with previous data on the photosynthetic response of algae to oxygen concentration, indicate that the photosynthetic apparatus of higher plants differs considerably from that of algae in its sensitivity to oxygen.
The inhibitory effect of oxygen on photosynthetic Co 2 fixation in higher plants is somewhat higher at wavelengths which excite preferentially photosystem I. Also, the Emerson enhancement of Co 2 fixation measured when a far red beam of low intensity is imposed on a background of red light is greater under low oxygen concontrution than under air. Measurements of reversible light‐induced absorbance changes reveal that the change at 591 nm, probably caused by pla.stocyanin, is affected by oxygen concentration only if photosystem II is excited. the reducing effect on plastocyanin, caused by excitation of this system, decreases with increasing oxygen concentration. From these results it is suggested that a possible site of the inhibition by oxygen is in the electron carrier chain between the two photosystems. Oxygen might act as an electron acceptor at this site, causing reducing power to react back with molecular oxygen. However, this hypothesis does not account for equal inhibitions of the quantum yield and the light saturated rate of photosynthetic CO 2 uptake.
Through the photosynthetic process plants take up carbon dioxide and evolve oxygen. The present high concentration of molecular oxygen in the atmosphere is generally considered to have arisen from the activity of photo‐synthetic organisms. The effect of oxygen concentration would seem, therefore, to he a problem of great interest, not only in the field of the biophysics and biochemistry of photosynthesis, but in ecology and other branches of biology as well.
It was discovered by Warburg (1920) that high concentrations of oxygen inhibit the rate of photosynthetic oxygen evolution in the unicellular alga Chlorella . Since then, it has been confirmed by various authors that oxygen cconcentrations in the range 21–100 per cent have a marked inhibitory effect on photosynthesis, particularly at saturating light intensities. There is some evidence that under conditions when carbon dioxide concentration limits photosynthesis, the inhibition may become obvious even in 21 per cent oxygen. The inhibition has not been considered to operate at low light intensities. A review on the subject has been given by Turner and Brittain (1962).
Various hypotheses have been put forward to explain the inhibitory effect of oxygen, commonly referred to as the Warhurg effect. Some authors favor the idea of enzyme inhibition; Turner et al . (1958) that one or more enzymes of the carbon reduction cycle are inactivated by oxygen: lirianlals (1962) that enzymes of the oxygen‐evolving complex are inhihited. Other hypotheses concern back‐reactions in which molecular oxygen is taken up, thus reversing the photosynthetic process. These reactions include photo‐oxidation, photorespiration, and the Mehler reaction (Tamiya et al ., 1957). At present, there is no generally accepted hypothesis explaining the effect.
The often conflicting results on which these hypotheses were based have been obtained mostly on algae. The first observation of an inhibitory effect on photosynthesis in a higher plant was made hy McAlister and Myers (1940) in wheat leaves. They found that the photosyntlietic CO 2 uptake was markedly lower in air than in an atmosphere of about 0.5 per cent oxygen. At the CO 2 concentration used (0.03%) the inhibition was present both at high and moderate light intensities. No data were obtained at low light intensities.
Although the study of the effect of oxygen concentration on photosynthesis in higher plants would seem to be of great interest, particularily since the natural environment of most land plants is an atmosphere with an oxygen content of 21 per cent, it has attracted very little attention. To the author's knowledge no thorough investigation on the subject has been published.
The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO 2 fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO 2 fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae.
A stepwise multiple regression analysis was used in an attempt to correlate statistically the geographic patterns in the abundance of C4 grasses with patterns in climatic variables. The percent of grasses having the C4 pathway was computed for the total grass flora in twenty-seven widely spaced regions of North America. From long-term climatic records seasonal and annual values for solar irradiance, water supply, heat availability, and combinations of these variables were assigned to each of the twentyseven regions. The results of the analysis suggest that high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C4 grass species in a regional flora. It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C4 pathway in cooler habitats.
The measurements were made to provide a basis for discussion of the definition of “photosynthetically active radiation”. The action spectrum, absorptance and spectral quantum yield of CO2 uptake were measured, for leaves of 22 species of crop plant, over the wavelength range 350 to 750 nm. The following factors were varied: species, variety, age of leaf, growth conditions (field or growth chamber), test conditions such as temperature, CO2 concentration, flux of monochromatic radiation, flux of supplementary white radiation, orientation of leaf (adaxial or abaxial surface exposed). For all species and conditions the quantum yield curve had 2 broad maxima, centered at 620 and 440 nm, with a shoulder at 670 nm. The average height of the blue peak was 70% of that of the red peak. The shortwave cutoff wavelength and the height of the blue peak varied slightly with the growth conditions and with the direction of illumination, but for the practical purpose of defining “photosynthetically active radiation” the differences are probably insignificant. The action spectrum for photosynthesis in wheat, obtained by Hoover in 1937, could be duplicated only with abnormally pale leaves.
A selection of C4 species was surveyed to determine the relationship between their content of C4 acid decarboxylating enzymes, the activities of several other enzymes implicated in the C4 pathway, and their anatomical and ultrastructural features. The species examined clearly fell into three groups according to whether they contained high levels of either NADP malic enzyme (EC 1.1.1.40), phosphoenolpyruvate carboxykinase (EC 4.1.1.49) or NAD malic enzyme (EC 1.1 .1.39). The occurrence of high NADP malic enzyme activity was always associated with higher NADP malate dehydrogenase activity, while those species distinguished by high activities of either of the other two decarboxylases invariably contained high aspartate aminotransferase and alanine amino- transferase activities. Each of these decarboxylating enzymes was located in bundle sheath cells. NAD malic enzyme, but not phosphoenolpyruvate carboxykinase, was associated with mitochondria. Light and electron micrographs revealed differences between these groups with respect to the intracellular location of chloroplasts and mitochondria in bundle sheath cells, and the content and ultrastructure of mitochondria. The trend was for species with high NAD malic enzyme to contain the most mitochondria in the bundle sheath cells with apparently the most extensively developed cristae membrane systems. However, mitochondrial respiratory enzyme activities were similar for the three groups of species. The basic similarities and differences between the three groups of C4 plants distinguished by their differing C4 acid decarboxylating systems are discussed, and schemes for the probable photosynthetic reactions in bundle sheath cells are presented. A nomenclature to distinguish between these groups is proposed.
An oxygen-dependent production of phosphoglycolate is catalyzed by purified soybean ribulose diphosphate carboxylase and by crude extracts of soybean and corn leaves. It is suggested that the phosphoglycolate produced in this reaction is the source of glycolate metabolized in photorespiration.
A high-affinity form of ribulose diphosphate carboxylase, observed transiently in spinach-leaf extracts soon after extraction, was inhibited by O2 competitively with respect to CO2. Analogously, the ribulose diphosphate oxygenase activity for this form was inhibited by CO2, competitively with respect to O2. For each gas, the Km for the reaction in which it was a substrate was similar to its Ki for the reaction it inhibited. The Arrhenius activation energy for the oxygenase reaction was 1.5 times that of the carboxylase. These characteristics are consistent with ribulose diphosphate oxygenase being the enzymatic reaction responsible for synthesizing the substrate for photorespiration and with the concept that the balance between photosynthesis and photorespiration of leaves is a reflection of the ratio between the two activities of this bi-functional enzyme.
This chapter discusses the localized altered regions or the damaged strands of DNA that are altered by ultraviolet (UV) irradiation. If there is some denaturation of DNA during irradiation, there will be an enhancement of forming certain photoproducts in these denatured regions. It is reasonable that localized denatured regions should occur in irradiated DNA as many of the photoproducts will alter internucleotide spacings, disrupt normal hydrogen bonding, and cause a loss of base stacking. Hence, as the radiation dose increases, the likelihood of forming photoproducts favored by single-stranded DNA increases. The mechanisms of detection that are used to determine and locate the altered strands of DNA can be broken down into two broad categories—qualitative detection, which can be achieved through physical method, chemical analysis, and biochemical means, and quantitative measures like thermal melting analysis and kinetic formaldehyde method.
The effect of 21% O(2) and 3% O(2) on the CO(2) exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2 degrees and 43 degrees , CO(2) concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O(2) compared to 3% O(2). The degree of inhibition increased with increasing temperature and decreasing CO(2) concentration. Light intensity did not alter the effect of O(2) except at light intensities or CO(2) concentrations near the compensation point. At high CO(2) concentrations and low temperature, O(2) inhibition of apparent photosynthesis was absent. At 3% O(2), wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30 degrees , and a CO(2) compensation point of less than 0.0005% CO(2). The effect of O(2) on apparent photosynthesis could be ascribed to a combination of stimulation of CO(2) production during photosynthesis, and inhibition of photosynthesis itself.
Photosynthesis and Photorespiration
- Slatyer
Slatyer, eds., Photosynthesis and Photorespiration. Wiley Interscience, New York. pp. 130-136.
Photosynthesis by sugar-cane leaves
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HATCH, M. D. AND C. R. SLACK. 1966. Photosynthesis by sugar-cane leaves. Biochem. J.
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Relationships between nitrogen level, photosynthetic capacity, and carboxydismutase activity in Atriplex patula leaves
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MEDINA, E. 1970. Relationships between nitrogen level, photosynthetic capacity, and
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Photosynthesis, Photorespiration, and Plant Productivity Academic Press, New York. 347 pp. www.plant.org on July 16, 2015 -Published by www.plantphysiol.org Downloaded from Copyright
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ZELrrCH, I. 1971. Photosynthesis, Photorespiration, and Plant Productivity. Academic
Press, New York. 347 pp.
www.plant.org
on July 16, 2015 -Published by
www.plantphysiol.org
Downloaded from
Copyright © 1977 American Society of Plant Biologists. All rights reserved.
Phosphoglycolate production catalyzed by ribulose diphosphate carboxylase
- G Bowes
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BOWES, G., W. L. OGREN, AND R. H. HAGEMEN. 1971. Phosphoglycolate production
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