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Photosynthesis-Irradiance curves performed on different leaf sections from 2 nd youngest leaves of C. nodosa (a), Z. marina (b) and Z. noltei (c). Data represent mean ± SE (n = 5).
Source publication
Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels (meadow, shoot, leaf and chloroplast level). Yet, comparative studies, to identify species’ strategies, and integration of the relative importance of photoacclimatory adjustments at differ...
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Typical symptoms of potassium deficiency, characterised as chlorosis or withered necrosis, occur concomitantly with down-regulated photosynthesis and impaired leaf water transport. However, the prominent limitations and mechanisms underlying the concerted decreases of leaf photosynthesis and hydraulic conductance are poorly understood. Monocots and...
Citations
... However, their presence in shallow areas indicates that they have developed coping mechanisms to endure high light stress. These mechanisms include excess light energy dissipation from the light-harvesting antenna (Ralph and Burchett, 1995;Buapet et al., 2017;Schubert et al., 2018;Fang et al., 2020), chloroplast avoidance movement (Buapet et al., 2020;Saewong et al., 2022), antioxidative networks (Phandee and Buapet, 2018;Buapet et al., 2020;Saewong et al., 2022), and morphological plasticity (Kaewsrikhaw et al., 2016;Azcárate-García et al., 2020). Together, these abilities enable seagrasses to maintain their photosynthetic activity and support growth even under intense light environments. ...
... For instance, P. oceanica (large and "persistent" sensu Kilminster et al., 2015) and H. stipulacea (small and "colonizing" sensu Kilminster et al., 2015) both have extremely wide vertical ranges, from 0 to 45 and 70 m, respectively. The ability to colonize wide vertical ranges and adjust to changing light conditions is therefore dependent not merely on species-specific traits, but on the acclimatization potential of those traits (Schubert et al., 2018). ...
... In a similar vein, recent studies with several Mediterranean macroalgae show that their depth distributional range is closely related to speciesspecific photo-acclimatization capacities and light-harvesting strategies (Sant & Ballesteros, 2021). However, most studies of light acclimatization in seagrasses focus on a single species and often do not study plant responses across organizational levels (Schubert et al., 2018). A more holistic approach is required to understand how the ability of species to acclimatize by modulating particular seagrass traits can mediate differences in their vertical distribution. ...
Aim
The global vertical depth distribution of seagrass species remains poorly understood. Locally, the abundance and distribution of seagrasses is determined by light penetration, but at global levels each seagrass species has very distinct maximum distributional depth ranges, indicating that plant-associated traits must also influence their specific depth ranges. Seagrass-specific attributes, such as plant size or architecture, growth or reproductive strategy and their physiological and/or morphological acclimatization potential, have been suggested to be responsible for this variety of vertical distributions. We investigate here whether these species-specific traits drive differences in the global maximum vertical distribution of seagrasses.
Location
Global.
Time period
Publications between 1982 and 2020.
Major taxa studied
Seagrasses (order Alismatales).
Methods
We tested whether the species-specific maximum vertical distribution of seagrasses can be predicted by (1) their rhizome diameter (a proxy for plant size); (2) their functional resilience (growth/reproductive strategy); or (3) their acclimatization capacity. For the last aspect, we used a systematic review followed by meta-analytical approaches to select key seagrass traits that could potentially acclimatize to extreme light ranges across different seagrasses.
Results
We found that vertical distribution is best explained by the species-specific acclimatization capacity of various seagrass traits, including saturation irradiance (physiological trait), leaves per shoot (morphological trait) and above-ground biomass (structural trait). In contrast, our results indicate no predictive power of seagrass size or growth/reproductive strategy on the vertical distribution of seagrasses.
Main conclusions
Across the globe, the ability of seagrass species to thrive at a wide range of depths is strongly linked to the species-specific acclimatization capacity of key traits at different organizational levels.
... More recent studies demonstrated the influence of oxygen concentrations and temperature on photorespiration in seagrass that fluctuate in natural environment because of eutrophication, high community productivity and elevated ocean temperatures; and therefore, will play a role in predicting the health status of these plants in warmer climate scenarios (Buapet and Björk, 2016;Rasmusson et al., 2020). The plastochron interval, which defines leaf life span, leaf turnover and elongation rates, plays an important role in photoacclimation strategies that differ among species at the chloroplast, leaf and shoot levels (Schubert et al., 2018). However, we still do not understand how long-term acclimation to climate warming and ocean acidification/ carbonation will affect photorespiration and photoprotection in seagrasses (Koch et al., 2013). ...
Photorespiration, commonly viewed as a loss in photosynthetic productivity of C3 plants, is expected to decline with increasing atmospheric CO2, even though photorespiration plays an important role in the oxidative stress responses. This study aimed to quantify the role of photorespiration and alternative photoprotection mechanisms in Zostera marina L. (eelgrass), a carbon-limited marine C3 plant, in response to ocean acidification. Plants were grown in controlled outdoor aquaria at different [CO2]aq ranging from ~55 (ambient) to ~2121 μM for 13 months and compared for differences in leaf photochemistry by simultaneous measurements of O2 flux and variable fluorescence. At ambient [CO2], photosynthesis was carbon limited and the excess photon absorption was diverted both to photorespiration and non-photochemical quenching (NPQ). The dynamic range of NPQ regulation in ambient grown plants, in response to instantaneous changes in [CO2]aq, suggested considerable tolerance for fluctuating environmental conditions. However, 60 to 80% of maximum photosynthetic capacity of ambient plants was diverted to photorespiration resulting in limited carbon fixation. The photosynthesis to respiration ratio (P E : R D) of ambient grown plants increased 6-fold when measured under high CO2 because photorespiration was virtually suppressed. Plants acclimated to high CO2 maintained 4-fold higher P E : R D than ambient grown plants as a result of a 60% reduction in photorespiration. The O2 production efficiency per unit chlorophyll was not affected by the CO2 environment in which the plants were grown. Yet, CO2 enrichment decreased the light level to initiate NPQ activity and downregulated the biomass specific pigment content by 50% and area specific pigment content by 30%. Thus, phenotypic acclimation to ocean carbonation in eelgrass, indicating the coupling between the regulation of photosynthetic structure and metabolic carbon demands, involved the downregulation of light harvesting by the photosynthetic apparatus, a reduction in the role of photorespiration and an increase in the role of NPQ in photoprotection. The quasi-mechanistic model developed in this study permits integration of photosynthetic and morphological acclimation to ocean carbonation into seagrass productivity models, by adjusting the limits of the photosynthetic parameters based on substrate availability and physiological capacity.
... The thickness of P. oceanica leaves shows a vertical gradient that decreases from the basal to the apical region. This observation confirms studies carried out in other areas of the Mediterranean (Colombo et al., 1983;Dalla Via et al., 1998), including for other marine Magnoliophyta species such as Cymodocea nodosa (Ucria) Asch (Schubert et al., 2018) and Thalassia testudinum Banks and Solander ex König (Enríquez, 2005). The trend observed in this study may be related to the growth of the P. oceanica leaves from a basal meristem that allows the plant to continue growing when the apical older regions become senescent and less chlorophyllous (Kuo & den Hartog, 2006;Ruocco et al., 2019). ...
There is little research on the distribution and evolution of tannin cells, specialized in the sequestration of phenolic compounds, in the leaves of P. oceanica, depending on the developmental stage and environmental conditions. This work aims to evaluate the density of tannin cells along the vertical axis of leaves (basal, middle, and apical regions) at four sites corresponding to an anthropogenic gradient estimated from the ecological status of P. oceanica meadows: Moderate (El Djamila), Good (Bou Ismaïl) and very good (Kouali and Aïn Tagouraït). Leaf thickness and width were measured in each region to express the density of tannin cells per mm². Data analysis shows that the density of tannin cells decreases with increasing leaf age and that the highest densities are recorded in the apical regions, especially when the leaf apex is entire. The density of leaf tannin cells is significantly correlated (R = -0.977, p = 0.022) with the Ecological Quality Ratio (EQR) corresponding to the ecological status of P. oceanica meadows and reflecting the impact of environmental pressures. This sensitivity to environmental conditions opens interesting prospects for using tannin cell density as a descriptor (environmental biomarker) in coastal monitoring programs based on P. oceanica meadows.
... www.nature.com/scientificreports/ than in old tissues, which has been shown to be a common feature related to the reduction of leaf thickness and cell layers towards the tip 45 . Nonetheless, in our work, this feature was not noticeable during heatwave recovery, which may be related to the increased area vs DW ratio in heatwave recovering leaves, as discussed below. ...
Marine heatwaves (MHWs) are increasing in frequency and intensity as part of climate change, yet their impact on seagrass is poorly known. The present work evaluated the physiological and morphological responses of Cymodocea nodosa to a MHW. C. nodosa shoots were transplanted into a mesocosm facility. To simulate a MHW, water temperature was raised from 20 to 28 °C, kept 7 days at 28 °C, cooled down back to 20 °C and then maintained at 20 °C during an 8-day recovery period. The potentially stressful effects of the simulated heatwave on the photosynthetic performance, antioxidative-stress level and area vs dry weight ratio of leaves were investigated. The maximum quantum yield of photosystem II (ΦPSII) increased during the heatwave, allowing the plants to maintain their photosynthetic activity at control level. Negative effects on the photosynthetic performance and leaf biomass of C. nodosa were observed during the recovery period. No significant oxidative stress was observed throughout the experiment. Overall, although C. nodosa showed a relative tolerance to MHWs compared to other species, its population in Ria Formosa is likely to be negatively affected by the forecasted climate change scenarios.
... Thus, longer monitoring after a change in light availability in seagrass beds is recommended. Early investigations also suggested that integrating biomarkers across biological organizations is effective in assessing impacts of various stressors on seagrass health (Schubert et al., 2018;Kerninon et al., 2021;Yucharoen et al., 2021). These topics deserve further investigation. ...
Seagrass meadows can improve water quality through their nutrient removal capacity. However, this key ecosystem function might be affected by reduced light availability in the water column through impacts on seagrass photosynthesis. Photosynthesis provides energy and carbon skeletons for nitrogen uptake and assimilation in plants – a reduction in photosynthetic capacity should alter nitrogen metabolism. In our study, we explored how nitrogen metabolism in a common tropical seagrass, Halophila ovalis, responded as the plant photo-acclimated to reduced light levels. H. ovalis was exposed to various shading levels (0% control, 25% and 50%) in the field at Chek Jawa, Singapore for 28 days. Photo-acclimation was tracked by measuring light use characteristics through PAM fluorometry (rapid light curves) and protein expression pertaining to photosynthetic processes (RbcL, PsbA and PsbS). Nitrate and ammonium uptake rates were assessed in leaves and root-rhizome complexes, and plant tissue nutrients (carbon and nitrogen) were quantified at the end of the experiment. Shaded plants displayed significant photoacclimation responses, such as lower maximum electron transport rates (ETRmax) and saturating irradiance (Ek), as well as a down-regulation of PsbA and PsbS. Several parameters (ETRmax, Ek and PsbS protein levels) were identified to be promising candidates for monitoring impacts of light reduction on seagrass health and warrant further investigations. As the seagrass acclimated to reduced light levels, a shift in nitrogen use was observed through a reduction in relative nitrate uptake rates in the leaves and root-rhizome complexes, and an increase in relative ammonium uptake rates in the leaves. This signaled potential modifications in nutrient removal capacity, via nitrogen uptake, for seagrasses in low light conditions. Carbon-to‑nitrogen ratio in plant tissue and the expression of RbcL did not exhibit significant change with light reduction. Our findings highlight that inter-related processes of photosynthesis and nitrogen assimilation should be considered when evaluating the potential impacts of light reduction on seagrass meadows and the ecosystem functions they provide.
... For example, rapid adjustments to a new constant irradiance take place in a matter of days through subcellular photosynthetic changes (Lambers et al., 2008). On the other hand, photoacclimation, i.e., photosynthetic, physiological, and morphological adjustments to light conditions may take weeks to months, and occur from subcellular to plant scale (McMahon et al., 2013;Schubert et al., 2018). At shoot scale, an increase in leaf surface or photosynthetic biomass, often approximated by an increase of the above or below-ground biomass ratio, helps maintain carbon balance by decreasing the proportion of non-photosynthetic tissues relative to photosynthetic ones (Olesen and Sand-Jensen, 1993). ...
... The subtle change in carotenoid contents with light intensity can be related to the preservation of heat dissipation mechanisms, as mentioned above, and/or to an optimization of light harvesting in low-light environments (Silva et al., 2013;Davey et al., 2018). Changes in pigment contents are often considered as photoacclimatory mechanisms enabling better light absorption (Ralph et al., 2007;Schubert et al., 2018). However, the adaptation of seagrasses to the aquatic life, consisting of concentrating the chloroplasts in the leaf epidermis to optimize inorganic carbon acquisition (Hemminga and Duarte, 2000;Enríquez, 2005), leads to a strong package effect (Cummings and Zimmerman, 2003;Enríquez, 2005;Durako, 2007). ...
Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m–2 s–1, 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m–2 s–1, which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m–2 s–1, while a compensation point (NPP = 0) of 13.7 μmol photons m–2 s–1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves’ light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents an MQR value for eelgrass in the St. Lawrence estuary, which is highly pertinent in the context of conservation and restoration of eelgrass meadows.
... Our investigation solely focused on the youngest mature ramets as they represent a significant site with a fully developed structure and function. These youngest mature ramets are metabolically active, and they have been widely used in physiological investigations (Short & Duarte, 2001;Collier et al., 2008;Park et al., 2016;Schubert et al., 2018;Rasmusson et al., 2019;Nguyen et al., 2020). Following the literature mentioned above, we used the third ramet from the growing apex of C. rotundata and T. hemprichii and the second ramet from the growing apex of H. ovalis. ...
Background
The ability to maintain sufficient oxygen levels in the belowground tissues and the rhizosphere is crucial for the growth and survival of seagrasses in habitats with highly reduced sediment. Such ability varies depending on plant anatomical features and environmental conditions.
Methods
In the present study, we compared anatomical structures of roots, rhizomes and leaves of the tropical intertidal seagrasses, Cymodocea rotundata , Thalassia hemprichii and Halophila ovalis , followed by an investigation of their gas exchange both in the belowground and aboveground tissues and photosynthetic electron transport rates (ETR) in response to experimental manipulations of O 2 level (normoxia and root hypoxia) and temperature (30 °C and 40 °C).
Results
We found that C. rotundata and T. hemprichii displayed mostly comparable anatomical structures, whereas H. ovalis displayed various distinctive features, including leaf porosity, number and size of lacunae in roots and rhizomes and structure of radial O 2 loss (ROL) barrier. H. ovalis also showed unique responses to root hypoxia and heat stress. Root hypoxia increased O 2 release from belowground tissues and overall photosynthetic activity of H. ovalis but did not affect the other two seagrasses. More pronounced warming effects were detected in H. ovalis , measured as lower O 2 release in the belowground tissues and overall photosynthetic capacity (O 2 release and dissolved inorganic carbon uptake in the light and ETR). High temperature inhibited photosynthesis of C. rotundata and T. hemprichii but did not affect their O 2 release in belowground tissues. Our data show that seagrasses inhabiting the same area respond differently to root hypoxia and temperature, possibly due to their differences in anatomical and physiological attributes. Halophila ovalis is highly dependent on photosynthesis and appears to be the most sensitive species with the highest tendency of O 2 loss in hypoxic sediment. At the same time, its root oxidation capacity may be compromised under warming scenarios.
... However, as plants experience stressful conditions, to ensure their survival, they may be acclimatized by reallocating resources toward increased growth or alterations in morphology [41]. There is a need for an integrated (i.e., at different biological levels) study to assess plant response to stress [42]. ...
Stuckenia pectinata, submerged macrophyte of eutrophic to hyper-eutrophic fresh to brackish waters, faces management and climatic-forced increment of salinity and irradiance in Vistonis Lake (Greece) that may endanger its existence and the ecosystem functioning. A pre-acclimated clone under low irradiance and salinity conditions was treated to understand the effects of high salinity and irradiance on a suite of subcellular (chlorophyll a fluorescence kinetics and JIP-test, and chlorophyll content) to organismal (relative growth rate—RGR) physiological parameters. The responses to high irradiance indicated the plant’s great photo-acclimation potential to regulate the number and size of the reaction centers and the photosynthetic electron transport chain by dissipation of the excess energy to heat. A statistically significant interaction (p < 0.01) of salinity and irradiance
on Chl a, b content indicated acclimation potential through adjusting the Chl a, b contents. However, no significant (p > 0.05) difference was observed on Chl a/b ratio and the RGR, indicating the species’ potential to become acclimatized by reallocating resources to compensate for growth. Thus, the regulation of photosynthetic pigment content and photosystem II performance consisted of the primary growth strategy to present and future high salinity and irradiance stressful conditions due to eutrophication management and the ongoing climatic changes.
... This result indicates a general homogeneous level of photo-adaptation of P.oceanica at the three monitored stations, belonging to the same genetic unit [69]. Moreover, based on the evidence from studies regarding photoacclimation, P. oceanica is a species with a low physiological plasticity [47,91,97]. As a climax species with a longer life span, it regulates more strongly at the leaf, shootand meadowlevel in response to light availability [98][99][100] than it does at the physiological level, in contrast to seagrass species with shorter life spans. ...
Posidonia oceanica (L.) Delile meadows are recognized to be one of the most productive ecosystems of the Mediterranean basin. Due to the impacts of human activities in coastal areas, seagrasses are experiencing a critical decline. In this context, the understanding of the dynamics of production and photosynthesis in response to the environmental factors is essential to address efficient conservation strategies that limit this trend and to assess the ecological status of marine ecosystems. Pulse Amplitude Modulated (PAM) fluorometry has been widely implemented to assess seagrass health and productivity. Here we analyzed the photosynthetic dynamics of P. oceanica according to its bathymetric distribution and daily light availability along a depth gradient to be used as baseline for monitoring purposes on the health status of the seagrass meadows in the Northern Tyrrhenian Sea. Moreover, to investigate the effects of the environmental factors on the health status of P. oceanica within the study area through a multidisciplinary approach, the models contained in the Civitavecchia Coastal Environmental Monitoring System were used. In this study, significant photo-physiological changes have been observed among the investigated meadows. Moreover, the integration of physiological and hydrodynamic information allowed the description of how P. oce-anica modulates its photosynthetic capacity at different environmental conditions.
