Photosynthetic Acclimation Research Articles

Evidence for widespread thermal acclimation of canopy photosynthesis.

Plants acclimate to temperature by adjusting their photosynthetic capacity over weeks to months. However, most evidence for photosynthetic acclimation derives from leaf-scale experiments. Here we address the scarcity of evidence for canopy-scale photosynthetic acclimation by examining the correlation between maximum photosynthetic rates (Amax,2,000) and growth temperature ( ) across a range of concurrent temperatures and canopy foliage quantity, using data from >200 eddy covariance sites. We detect widespread thermal acclimation of canopy-scale photosynthesis, demonstrated by enhanced Amax,2,000 under higher , across flux sites with adequate water availability. A 14-day period is identified as the most relevant timescale for acclimation across all sites, with a range of 12-25 days for different plant functional types. The mean apparent thermal acclimation rate across all ecosystems is 0.41 (-0.38-1.04 for 5th-95th percentile range) µmol m-2 s-1 °C-1, with croplands showing the largest acclimation rates and grasslands the lowest. Incorporating an optimality-based prediction of leaf photosynthetic capacities into a biochemical photosynthesis model is shown to improve the representation of thermal acclimation. Our results underscore the critical need for enhanced understanding and modelling of canopy-scale photosynthetic capacity to accurately predict plant responses to warmer growing seasons.

Leaf Photosynthetic and Photoprotective Acclimation in the Ultraviolet-A1 and Blue Light Regions Follow a Continuous, Shallow Gradient.

Although blue light is known to produce leaves with high photosynthetic capacity, the role of the blue-adjacent UV-A1 (350-400 nm) in driving leaf photosynthetic acclimation is less studied. Tomato plants were grown under hybrid red and blue (RB; 95/5 μmol m-2 s-1), as well as four treatments in which RB was supplemented with 50 μmol m-2 s-1 peaking at 365, 385, 410 and 450 nm, respectively. Acclimation to 365-450 nm led to a shallow gradient increase in trait values (i.e., photosynthetic capacity, pigmentation and dry mass content) as the peak wavelength increased. Furthermore, both UV-A1 and blue light grown leaves showed efficient photoprotection under high light intensity. When treated plants were transferred to fluctuating light for 5 days, leaves from all treatments showed increases in photosynthetic capacity, which were strongest in RB, followed by additional UV-A1 treatments; RB grown leaves showed reductions in maximum quantum yield of photosystem II, while UV-A1 grown leaves showed increases. We conclude that both UV-A1 and blue light effectively trigger photosynthetic and photoprotective acclimation, the extent of acclimation becoming stronger the longer the peak wavelength is. Acclimatory responses to UV-A1 and blue light are thus not distinct from one another, but follow a continuous gradient.

The interplay between LHCSR and PSBS proteins provides photoprotection in Chlamydomonas reinhardtii pgr5 mutant under high light

Cyclic electron transport (CET) is a vital alternative route that protects against photodamage and aids in energy production. This process depends on proton gradient regulation 5 (PGR5) and PGRL1-dependent pathways associated with CET. The exact roles of these proteins in photosystem I photochemistry under prolonged high light conditions are not fully understood. Continuous light adaptation hinges on two critical mechanisms: alterations in the proton motive force (pmf) and adjustments in the ratio of proteins activated by high light that dissipate excess light through non-photochemical quenching (NPQ). To explore this, we studied pgrl1 and pgr5 mutants to gauge their roles in balancing photochemistry and photoacclimation. These mutants showed inhibited growth, reduced photosynthetic efficiency, and a lowered pmf, leading to diminished non-photochemical energy quenching (qE) under high light. Prolonged high light exposure slowed down unregulated energy losses Y(NO), and relaxation helped regulate photosynthetic activity by increasing photoinhibitory quenching (qI), thus preventing further damage to the photosystem. The precise balance between the two pmf components, ΔpH and Δψ, is critical for controlling photochemistry and photoacclimation, yet remains elusive. In pgr5 reduced pmf led to an accumulation of cytochrome b6f under high light, and a decrease in the ΔpH component increased the Δψ component's role in photosynthetic acclimation. Notably, light-harvesting complex stress response protein 3 (LHCSR3) showed decreased expression in pgrl1, whereas pgr5 exhibited no expression of both LHCSR3 and LHCSR1 under high light conditions. Moreover, continuous increase in PSBS protein accumulation in pgr5 suggests enhanced photoprotection in the absence of LHCSR3 under high light. The study provides significant insights into how cyclic electron transport (CET) regulates photoprotective proteins LHCSR and PSBS, influencing Chlamydomonas' survival strategies.

Acclimation of Photosynthesis to CO2 Increases Ecosystem Carbon Storage due to Leaf Nitrogen Savings.

Photosynthesis is the largest flux of carbon between the atmosphere and Earth's surface and is driven by enzymes that require nitrogen, namely, ribulose-1,5-bisphosphate (RuBisCO). Thus, photosynthesis is a key link between the terrestrial carbon and nitrogen cycle, and the representation of this link is critical for coupled carbon-nitrogen land surface models. Models and observations suggest that soil nitrogen availability can limit plant productivity increases under elevated CO2. Plants acclimate to elevated CO2 by downregulating RuBisCO and thus nitrogen in leaves, but this acclimation response is not currently included in land surface models. Acclimation of photosynthesis to CO2 can be simulated by the photosynthetic optimality theory in a way that matches observations. Here, we incorporated this theory into the land surface component of the Energy Exascale Earth System Model (ELM). We simulated land surface carbon and nitrogen processes under future elevated CO2 conditions to 2100 using the RCP8.5 high emission scenario. Our simulations showed that when photosynthetic acclimation is considered, photosynthesis increases under future conditions, but maximum RuBisCO carboxylation and thus photosynthetic nitrogen demand decline. We analyzed two simulations that differed as to whether the saved nitrogen could be used in other parts of the plant. The allocation of saved leaf nitrogen to other parts of the plant led to (1) a direct alleviation of plant nitrogen limitation through reduced leaf nitrogen requirements and (2) an indirect reduction in plant nitrogen limitation through an enhancement of root growth that led to increased plant nitrogen uptake. As a result, reallocation of saved leaf nitrogen increased ecosystem carbon stocks by 50.3% in 2100 as compared to a simulation without reallocation of saved leaf nitrogen. These results suggest that land surface models may overestimate future ecosystem nitrogen limitation if they do not incorporate leaf nitrogen savings resulting from photosynthetic acclimation to elevated CO2.

Acclimation Unifies the Scaling of Carbon Assimilation Across Climate Gradients and Levels of Organisation.

The temperature dependence of carbon assimilation-from leaf photosynthesis to ecosystem productivity-is hypothesised to be driven by the kinetics of Rubisco-catalysed carboxylation and electron transport. However, photosynthetic physiology acclimates to changes in temperature, which may decouple temperature dependencies at higher levels of organisation from the acute temperature sensitivity of photosynthesis. Here, we integrate relative growth rate theory, metabolic theory and biochemical photosynthesis theory to develop a carbon budget model of plant growth that accounts for photosynthetic acclimation to temperature. We test its predictions using a novel experimental approach enabling concurrent measurement of the temperature sensitivity of acute photosynthesis, acclimated photosynthesis and growth rate. We demonstrate for the first time that photosynthetic acclimation mediates how carbon assimilation kinetics 'scale up' from leaf photosynthesis to whole-plant growth. We also find that existing models of photosynthetic acclimation are unable to predict features of growth rate responses to temperature in our system.

The blue-green light-dependent state transition in the marine phytoplankton Ostreococcus tauri.

We explored the adaptive mechanisms of Ostreococcus tauri, a marine picophytoplankton with a ubiquitous ocean presence. We aimed to understand its photosynthetic acclimation, as featured in the cryo-EM structure of its photosystem I (PSI) supercomplex. This structure revealed a unique composition involving a phosphorylated Lhcp trimer bound to the PSI core along with two additional Lhcp trimers, suggesting potential state transitions for photoacclimation. To investigate this hypothesis, we conducted a series of biochemical and physiological experiments. We analyzed absorption spectra to differentiate between PSI and PSII, particularly focusing on blue-green wavelengths, and examined the effects of specific excitation of Lhcp with green light, including its phosphorylation and the formation of the PSI-LHCI-Lhcp supercomplex. Our experiments clarified the distinctive effects attributable to absorption by pigments associated with Lhcp. Exciting Lhcp with green light induced its phosphorylation, leading to the formation of the PSI-LHCI-Lhcp supercomplex. Notably, the functional antenna size of PSI could reversibly expand in response to green light, demonstrating its state transition capability. These findings not only highlight the unique photosynthetic acclimation adapted to the marine environment but also suggest a possible ancestral role of state transitions in green plants, given the phylogenetic position of Prasinophyceae.

The leaf-scale mass-based photosynthetic optimization model better predicts photosynthetic acclimation than the area-based.

Leaf-scale photosynthetic optimization models can quantitatively predict photosynthetic acclimation and have become an important means of improving vegetation and land surface models. Previous models have generally been based on the optimality assumption of maximizing the net photosynthetic assimilation per unit leaf area (i.e. the area-based optimality) while overlooking other optimality assumptions such as maximizing the net photosynthetic assimilation per unit leaf dry mass (i.e. the mass-based optimality). This paper compares the predicted results of photosynthetic acclimation to different environmental conditions between the area-based optimality and the mass-based optimality models. The predictions are then verified using the observational data from the literatures. The mass-based optimality model better predicted photosynthetic acclimation to growth light intensity, air temperature and CO2 concentration, and captured more variability in photosynthetic traits than the area-based optimality models. The findings suggest that the mass-based optimality approach may be a promising strategy for improving the predictive power and accuracy of optimization models, which have been widely used in various studies related to plant carbon issues.

Photosynthetic capacity in middle-aged larch and spruce acclimates independently to experimental warming and elevated CO2.

Photosynthetic acclimation to both warming and elevated CO2 of boreal trees remains a key uncertainty in modelling the response of photosynthesis to future climates. We investigated the impact of increased growth temperature and elevated CO2 on photosynthetic capacity (Vcmax and Jmax) in mature trees of two North American boreal conifers, tamarack and black spruce. We show that Vcmax and Jmax at a standard temperature of 25°C did not change with warming, while Vcmax and Jmax at their thermal optima (Topt) and growth temperature (Tg) increased. Moreover, Vcmax and Jmax at either 25°C, Topt or Tg decreased with elevated CO2. The Jmax/Vcmax ratio decreased with warming when assessed at both Topt and Tg but did not significantly vary at 25°C. The Jmax/Vcmax increased with elevated CO2 at either reference temperature. We found no significant interaction between warming and elevated CO2 on all traits. If this lack of interaction between warming and elevated CO2 on the Vcmax, Jmax and Jmax/Vcmax ratio is a general trend, it would have significant implications for improving photosynthesis representation in vegetation models. However, future research is required to investigate the widespread nature of this response in a larger number of species and biomes.

Singlet-Oxygen-Mediated Regulation of Photosynthesis-Specific Genes: A Role for Reactive Electrophiles in Signal Transduction.

During photosynthesis, reactive oxygen species (ROS) are formed, including hydrogen peroxide (H2O2) and singlet oxygen (1O2), which have putative roles in signalling, but their involvement in photosynthetic acclimation is unclear. Due to extreme reactivity and a short lifetime, 1O2 signalling occurs via its reaction products, such as oxidised poly-unsaturated fatty acids in thylakoid membranes. The resulting lipid peroxides decay to various aldehydes and reactive electrophile species (RES). Here, we investigated the role of ROS in the signal transduction of high light (HL), focusing on GreenCut2 genes unique to photosynthetic organisms. Using RNA seq. data, the transcriptional responses of Chlamydomonas reinhardtii to 2 h HL were compared with responses under low light to exogenous RES (acrolein; 4-hydroxynonenal), β-cyclocitral, a β-carotene oxidation product, as well as Rose Bengal, a 1O2-producing photosensitiser, and H2O2. HL induced significant (p < 0.05) up- and down-regulation of 108 and 23 GreenCut2 genes, respectively. Of all HL up-regulated genes, over half were also up-regulated by RES, including RBCS1 (ribulose bisphosphate carboxylase small subunit), NPQ-related PSBS1 and LHCSR1. Furthermore, 96% of the genes down-regulated by HL were also down-regulated by 1O2 or RES, including CAO1 (chlorophyllide-a oxygnease), MDH2 (NADP-malate dehydrogenase) and PGM4 (phosphoglycerate mutase) for glycolysis. In comparison, only 0-4% of HL-affected GreenCut2 genes were similarly affected by H2O2 or β-cyclocitral. Overall, 1O2 plays a significant role in signalling during the initial acclimation of C. reinhardtii to HL by up-regulating photo-protection and carbon assimilation and down-regulating specific primary metabolic pathways. Our data support that this pathway involves RES.

Forage legume responses to climate change factors

AbstractIncorporating forage legumes into grasslands is a recommended climate change mitigation strategy, but accruing desired benefits from legumes is contingent upon their resilience when exposed to climate change factors (CCF). Our objective was to synthesize literature describing responses to CCF of a broad array of forage legume species, including annuals and perennials from both temperate and tropical/subtropical regions. Most‐represented species in the related literature include alfalfa (Medicago sativa L.), various Trifolium and Lotus species, rhizoma peanut (Arachis glabrata Benth.), and capitata stylo (Stylosanthes capitata Vogel). The data indicate that while CCF effects on forage legumes can be generalized, interactions among CCF, species, and site‐specific soil/climate conditions may cause variation from expected responses. In most instances, exposing forage legumes to CO2 enrichment (eCO2) increased forage accumulation (FA), but elevated temperature (eT) often reduced the magnitude of the positive response to eCO2. Photosynthetic acclimation to eCO2 occurs in non‐N‐fixing plants, but legume nodules are large C sinks and drive sustained increases in legume FA to eCO2. Legume N2 fixation and the proportion of legume N derived from N2 fixation increase with eCO2, but the magnitude of the increases lessens with eT. Legume nutritive value (NV) responses to eCO2 are less pronounced than FA responses, but decreased herbage N and greater nonstructural carbohydrate concentrations are common. Exposure to eT negatively affects NV unless intervals between defoliation events are shortened. Limited data on reproductive performance show CCF affect flower number, pollen grain morphology and viability, and behavior of pollinators, potentially influencing legume reproductive success.

Biochemical versus stomatal acclimation of dynamic photosynthetic gas exchange to elevated CO2 in three horticultural species with contrasting stomatal morphology.

Understanding photosynthetic acclimation to elevated CO2 (eCO2) is important for predicting plant physiology and optimizing management decisions under global climate change, but is underexplored in important horticultural crops. We grew three crops differing in stomatal density-namely chrysanthemum, tomato, and cucumber-at near-ambient CO2 (450 μmol mol-1) and eCO2 (900 μmol mol-1) for 6 weeks. Steady-state and dynamic photosynthetic and stomatal conductance (gs) responses were quantified by gas exchange measurements. Opening and closure of individual stomata were imaged in situ, using a novel custom-made microscope. The three crop species acclimated to eCO2 with very different strategies: Cucumber (with the highest stomatal density) acclimated to eCO2 mostly via dynamic gs responses, whereas chrysanthemum (with the lowest stomatal density) acclimated to eCO2 mostly via photosynthetic biochemistry. Tomato exhibited acclimation in both photosynthesis and gs kinetics. eCO2 acclimation in individual stomatal pore movement increased rates of pore aperture changes in chrysanthemum, but such acclimation responses resulted in no changes in gs responses. Although eCO2 acclimation occurred in all three crops, photosynthesis under fluctuating irradiance was hardly affected. Our study stresses the importance of quantifying eCO2 acclimatory responses at different integration levels to understand photosynthetic performance under future eCO2 environments.

Assessing Structural Traits in Triticum aestivum and Zea mays for C3 and C4 Photosynthetic Differentiation Using Free-hand and Semi-thin Sections.

The enhanced efficiency of C4 photosynthesis, compared to the C3 mechanism, arises from its ability to concentrate CO2 in bundle sheath cells. The effectiveness of C4 photosynthesis and intrinsic water use efficiency are directly linked to the share of mesophyll and bundle leaf cells,size and density of bundle sheaths, and size, density, and cell wall thickness of bundle sheath cells. Rapid microscopical analysis of these traits can be performed on free-hand and semi-thin sections using conventional light microscopy, providing valuable information about photosynthetic efficiency in C4 crops by means of identifying and examining specific cell types. Additionally, errors in freehand and semi-thin section preparation that affect anatomical measurements and cell type diagnoses are shown, as well as how to avoid these errors. This microscopical approach offers an efficient means of gathering insights into photosynthetic acclimation to environmental variation and aids in the rapid screening of crops for future climates.

Photosynthetic Acclimation of Larch to the Coupled Effects of Light Intensity and Water Deficit in Regions with Changing Water Availability.

The impact of frequent water deficits on dominant tree species in boreal forests has received increased attention, particularly towards addressing the global climate change scenarios. However, the impacts of coupled light intensity and water deficit in the regeneration and growth of Larix gmelinii seedlings, a dominant species in China's boreal forests, are still unclear. We conducted a dual-factor controlled experiment with four light intensities (natural sunlight, 50% shading, 75% shading, and 90% shading) and three soil water conditions (80%, 60%, and 40% soil saturated water content). The results showed that the coupling of light and water has a significant effect on the growth and development of Larix gmelinii seedlings. In 40% of the saturated soil moisture content, net photosynthetic rate, transpiration rate, chlorophyll a, and total phenol-leaf were significantly lower than the same light conditions under 80% soil saturated water content. Under the coupling treatment of 60% soil saturated water content and 50% shading treatment, the plant height increment, net photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll a, and phenolic compound content were significantly higher than those of other coupling treatments; however, more than 75% shading inhibited photosynthetic parameters, chlorophyll a, total flavonoid-leaf, and total flavonoid-branch. Our results have important implications for forest management practices; they provide a scientific reference for the early growth of Larix gmelinii seedlings under the coupling of light and water and promote the survival and growth of seedlings.

Individual grain mass of inbred rice cultivars does not benefit from elevated [CO2]

Climate warming has led to a reduction of global crop yields. Elevated atmospheric [CO2] is believed to promote crop production by increasing photosynthesis, and thus partly offset the yield losses due to climate warming. However, photosynthetic acclimation may occur when the plant is exposed to long-term high [CO2] conditions, suggesting that elevated [CO2] (e[CO2]) might not bring benefits for cereal crops as the growing season proceeds. To assess the effect of long-term e[CO2] on rice yield, particularly on individual grain mass determined post-heading, we synthesized existing data from FACE (free-air CO2 enrichment) experiments across four locations in Japan and China. We also conducted a five-year field experiment with different [CO2] treatments using OTC (open-top chamber) facility. A novel experiment of pot replacement at heading was conducted in 2018 to evaluate the effect of post-heading e[CO2] on individual grain mass of rice. Meanwhile, we measured net photosynthetic rates under ambient [CO2] (a[CO2]) and e[CO2] (ambient + 200 μmol mol−1) at different developmental stages to identify the occurrence of photosynthetic acclimation. We show that FACE condition did not increase individual grain mass across thirty-six inbred rice cultivars at various rates of nitrogen application, and that the replacement of potted plants either from a[CO2] to e[CO2] or from e[CO2] to a[CO2] did not impact the individual grain mass. The yield benefit from e[CO2] was primarily attributed to an increase in the spikelet density determined pre-heading. We conclude that the individual grain mass of inbred rice does not benefit from e[CO2], which is most likely attributed to a loss of the advantage in CO2 gain induced by photosynthetic acclimation. Our findings suggest the necessity for selective breeding strategies to make better use of post-heading e[CO2] and for crop modelers to incorporate updated knowledge into models in the context of elevated [CO2].

Multigenerational Effects of Elevated CO2 and N Supply on Leaf Gas Exchange Traits in Wheat Plants

ABSTRACTThe responses of leaf gas exchange of wheat (Triticum aestivum L.) to elevated atmospheric CO2 concentration (e[CO2]) were often investigated within a single generation, while the long‐term acclimation of photosynthesis to growth in e[CO2] over multiple generations has not been systematically studied. Here, five wheat cultivars were grown under either ambient (a[CO2], 400 ppm) or elevated (e[CO2], 800 ppm) CO2 concentration for three consecutive generations (G1 to G3) with two N‐fertilisation levels (1N–1 g N pot−1 and 2N–2 g N pot−1) in climate‐controlled greenhouses. Leaf gas exchange was determined in each generation of plants under different treatments. It was found that at both N levels, e[CO2] stimulated photosynthetic rate while reducing stomatal conductance, transpiration rate and leaf N concentration, resulting in an enhanced water use efficiency and photosynthetic N use efficiency. The N level modulated the intergenerational responses of photosynthetic capacity to e[CO2]; under low N supply, the maximum carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and the rate of triose phosphate utilisation (TPU) were significantly downregulated by e[CO2] from the first to the second generation, but recovered in the third generation; whereas at high N levels, photosynthetic acclimation was diminished with the progress of generations, with Vcmax, Jmax and TPU increased under e[CO2] in the third generation. These results suggest that intergenerational adaptation could alleviate the e[CO2]‐induced reduction of the photosynthetic capacity, but plants with different N status responded differently to adapt to the long‐term exposure to e[CO2]. Among the five cultivars, 325Jimai showed a better photosynthetic performance under e[CO2] over the three generations, while 02‐1Shiluan appeared to be more inhibited by CO2 elevation in the long term conditions. These findings provide new insights for breeding strategies in the future CO2‐enriched environments.

A comprehensive assessment of photosynthetic acclimation to shade in C4 grass (Cynodon dactylon (L.) Pers.)

BackgroundLight deficit in shaded environment critically impacts the growth and development of turf plants. Despite this fact, past research has predominantly concentrated on shade avoidance rather than shade tolerance. To address this, our study examined the photosynthetic adjustments of Bermudagrass when exposed to varying intensities of shade to gain an integrative understanding of the shade response of C4 turfgrass.ResultsWe observed alterations in photosynthetic pigment-proteins, electron transport and its associated carbon and nitrogen assimilation, along with ROS-scavenging enzyme activity in shaded conditions. Mild shade enriched Chl b and LHC transcripts, while severe shade promoted Chl a, carotenoids and photosynthetic electron transfer beyond QA− (ET0/RC, φE0, Ψ0). The study also highlighted differential effects of shade on leaf and root components. For example, Soluble sugar content varied between leaves and roots as shade diminished SPS, SUT1 but upregulated BAM. Furthermore, we observed that shading decreased the transcriptional level of genes involving in nitrogen assimilation (e.g. NR) and SOD, POD, CAT enzyme activities in leaves, even though it increased in roots.ConclusionsAs shade intensity increased, considerable changes were noted in light energy conversion and photosynthetic metabolism processes along the electron transport chain axis. Our study thus provides valuable theoretical groundwork for understanding how C4 grass acclimates to shade tolerance.

Weaker photosynthetic acclimation to fluctuating than to corresponding steady UVB radiation treatments in grapevines

AbstractThe effects of transient increases in UVB radiation on plants are not well known; whether cumulative damage dominates or, alternately, an increase in photoprotection and recovery periods ameliorates any negative effects. We investigated photosynthetic capacity and metabolite accumulation of grapevines (Vitis vinifera Cabernet Sauvignon) in response to UVB fluctuations under four treatments: fluctuating UVB (FUV) and steady UVB radiation (SUV) at similar total biologically effective UVB dose (2.12 and 2.23 kJ m−2 day−1), and their two respective no UVB controls. We found a greater decrease in stomatal conductance under SUV than FUV. There was no decrease in maximum yield of photosystem II (Fv/Fm) or its operational efficiency (ɸPSII) under the two UVB treatments, and Fv/Fm was higher under SUV than FUV. Photosynthetic capacity was enhanced under FUV in the light‐limited region of rapid light‐response curves but enhanced by SUV in the light‐saturated region. Flavonol content was similarly increased by both UVB treatments. We conclude that, while both FUV and SUV effectively stimulate acclimation to UVB radiation at realistic doses, FUV confers weaker acclimation than SUV. This implies that recovery periods between transient increases in UVB radiation reduce UVB acclimation, compared to an equivalent dose of UVB provided continuously. Thus, caution is needed in interpreting the findings of experiments using steady UVB radiation treatments to infer effects in natural environments, as the stimulatory effect of steady UVB is greater than that of the equivalent fluctuating UVB.

Using leaf economic spectrum and photosynthetic acclimation to evaluate the potential performance of wintersweet under future climate conditions.

The function of landscape plants on the ecosystem can alleviate environmental issues of urbanization and global change. Global changes due to elevated CO2 affect plant growth and survival, but there is a lack of quantitative methods to evaluate the adaptability of landscape plants to future climate conditions. Leaf traits characterized by leaf economic spectrum (LES) are the universal currency for predicting the impact on plant ecosystem functions. Elevated CO2 usually leads to photosynthetic acclimation (PC), characterised by decreased photosynthetic capacity. Here, we proposed a theoretical and practical framework for the use of LES and PC to project the potential performance of landscape plants under future climatic conditions through principal component analysis, structural equation modelling, photosynthetic restriction analysis and nitrogen allocation analysis. We used wintersweet (an important landscaping species) to test the feasibility of this framework under elevated CO2 and different nitrogen (N) supplies. We found that elevated CO2 decreased the specific leaf area but increased leaf N concentration. The results suggest wintersweet may be characterized by an LES with high leaf construction costs, low photosynthetic return, and robust stress resistance. Elevated CO2 reduced photosynthetic capacity and stomatal conductance but increased photosynthetic rate and leaf area. These positive physio-ecological traits, e.g., larger leaf area (canopy), higher water use efficiency and stress resistance, may lead to improved performance of wintersweet under the predicted future climatic conditions. The results suggest planting more wintersweet in urban landscaping may be an effective adaptive strategy to climate change.

The combination of elevated CO2 and warmer temperature reduces photosynthetic capacity without diluting leaf N concentration in Amur linden (Tilia amurensis)

Abstract Elevated CO2 and warmer temperatures represent the future environmental conditions in the context of global change. A good understanding of plant response to their combined effects is, therefore, critically important for predicting future plant performance. This study investigated the photosynthetic acclimation of Amur linden (Tilia amurensis) seedlings (current year, about 60 cm tall), a shade-tolerant tree species in the temperate broadleaf deciduous forest, to the combination of current CO2 concentration and temperature (CC) and the combination of the predicted future CO2 concentration and temperature (FC). The results show that FC promoted aboveground growth, but reduced photosynthetic capacity (Vcmax: maximum rate of RuBP carboxylation and Jmax: maximum photosynthetic electron transport rate). However, the photosynthetic rate measured under the corresponding growth CO2 concentration was still higher under FC than under CC. FC depressed the photosynthetic limiting transition point (Ci-t, An-t) from Rubisco carboxylation to RuBP regeneration, i.e. An-t decreased without a change in Ci-t. FC did not change leaf N concentration but increased the total leaf N content per tree and photosynthetic nitrogen utilization efficiency. This suggests that N utilization, rather than photosynthetic capacity, may play an important role in the acclimation of the species to future climatic conditions. This study provides new insights into the photosynthetic acclimation of Amur linden and can be used to predict its possible performance under future climatic conditions.

Incorporating photosynthetic acclimation improves stomatal optimisation models.

Stomatal opening in plant leaves is regulated through a balance of carbon and water exchange under different environmental conditions. Accurate estimation of stomatal regulation is crucial for understanding how plants respond to changing environmental conditions, particularly under climate change. A new generation of optimality-based modelling schemes determines instantaneous stomatal responses from a balance of trade-offs between carbon gains and hydraulic costs, but most such schemes do not account for biochemical acclimation in response to drought. Here, we compare the performance of six instantaneous stomatal optimisation models with and without accounting for photosynthetic acclimation. Using experimental data from 37 plant species, we found that accounting for photosynthetic acclimation improves the prediction of carbon assimilation in a majority of the tested models. Photosynthetic acclimation contributed significantly to the reduction of photosynthesis under drought conditions in all tested models. Drought effects on photosynthesis could not accurately be explained by the hydraulic impairment functions embedded in the stomatal models alone, indicating that photosynthetic acclimation must be considered to improve estimates of carbon assimilation during drought.