Plant populations can undergo very localized adaptation, allowing widely distributed populations to adapt to divergent habitats in spite of recurrent gene flow. Neotropical trees—whose large and ...undisturbed populations often span a variety of environmental conditions and local habitats—are particularly good models to study this process. Here, we explore patterns of adaptive divergence from large (i.e., regional) to small (i.e., microgeographic) spatial scales in the hyperdominant Amazonian tree Eperua falcata Aubl. (Fabaceae) under a replicated design involving two microhabitats (~300 m apart) in two study sites (~300 km apart). A three‐year reciprocal transplant illustrates that, beyond strong maternal effects and phenotypic plasticity, genetically driven divergence in seedling growth and leaf traits was detected both between seedlings originating from different regions, and between seedlings from different microhabitats. In parallel, a complementary genome scan for selection was carried out through whole‐genome sequencing of tree population pools. A set of 290 divergence outlier SNPs was detected at the regional scale (between study sites), while 185 SNPs located in the vicinity of 106 protein‐coding genes were detected as replicated outliers between microhabitats within regions. Outlier‐surrounding genomic regions are involved in a variety of physiological processes, including plant responses to stress (e.g., oxidative stress, hypoxia and metal toxicity) and biotic interactions. Together with evidence of microgeographic divergence in functional traits, the discovery of genomic candidates for microgeographic adaptive divergence represents a promising advance in our understanding of local adaptation, which probably operates across multiple spatial scales and underpins divergence and diversification in Neotropical trees.
see also the Perspective by Christopher W. Dick.
Under natural conditions, plants are subjected to continuous changes of irradiance that drive variations of stomatal conductance to water vapour (gs). We propose a dynamic model to predict the ...temporal response of gs at the leaf level using an asymmetric sigmoid function with a unique parameter describing time constants for increasing and decreasing gs. The model parameters were adjusted to observed data using Approximate Bayesian Computation. We tested the model performance for (1) instant changes of irradiance; or (2) continuous and controlled variations of irradiance simulating diurnal time courses. Compared with the two mostly used steady‐state models, our dynamic model described daily time courses of gs with a higher accuracy. In particular, it was able to describe the hysteresis of gs responses to increasing/decreasing irradiance and the resulting rapid variations of intrinsic water‐use efficiency. Compared to the mechanistic model of temporal responses of gs by Kirschbaum, Gross & Pearcy, for which time constants were estimated with a large variance, our model estimated time constants with a higher precision. It is expected to improve predictions of water loss and water‐use efficiency in higher scale models by using a small number of parameters.
Under natural conditions, plants are subjected to continuous changes of irradiance that drive variations of stomatal conductance (gs). We propose a new dynamic model to predict the temporal response of gs to irradiance. Compared with widely used steady‐state models our dynamic model described daily time courses of gs with a higher accuracy. In particular, it was able to describe the hysteresis of gs responses to irradiance and the resulting rapid variations of intrinsic water‐use efficiency.
► The intention of the present review is to update the consensus knowledge on gm. ► Gaps in knowledge and research priorities are indicated for the near future. ► In particular, how has gm evolved ...among phylogenetically distant groups? ► Can gm be uncoupled from the water path regulation? ► Mechanistic models of gm incorpored in photosynthesis models are needed.
Mesophyll diffusion conductance to CO2 is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of gm, and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is large, and under certain conditions can be the most significant photosynthetic limitation. New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance.
Gaps in knowledge that should be research priorities for the near future include: how different is mesophyll conductance among phylogenetically distant groups and how has it evolved? Can mesophyll conductance be uncoupled from regulation of the water path? What are the main drivers of mesophyll conductance? The need for mechanistic and phenomenological models of mesophyll conductance and its incorporation in process-based photosynthesis models is also highlighted.
Leaf photosynthesis is known to acclimate to the actual irradiance received by the different layers of a canopy. This acclimation is usually described in terms of changes in leaf structure, and in ...photosynthetic capacity. Photosynthetic capacity is likely to be affected by mesophyll conductance to CO₂ which has seldom been assessed in tree species, and whose plasticity in response to local irradiance is still poorly known. Structural N and chlorophyll content, leaf mass to area ratio (LMA) and functional leaf traits maximum carboxylation rate (Vcmax), maximum light-driven electron flux (Jmax), and mesophyll conductance (gi) were assessed by measuring leaf response curves of net CO₂ assimilation versus intercellular CO₂ partial pressure, along a vertical profile across a beech canopy, and by fitting a version of the Farquhar model including gi. The measurements were repeated five times during a growth season to catch potential seasonal variation. Irradiance gradients resulted in large decreasing gradients of LMA, gi, Vcmax, and Jmax. Relative allocation of leaf N to the different photosynthetic processes was only slightly affected by local irradiance. Seasonal changes after leaf expansion and before induction of leaf senescence were only minor. Structural equation modelling confirmed that LMA was the main driving force for changes in photosynthetic traits, with only a minor contribution of leaf Nitrogen content. In conclusion, mesophyll conductance to CO₂ displays a large plasticity that scales with photosynthetic capacity across a tree canopy, and that it is only moderately (if at all) affected by seasonal changes in the absence of significant soil water depletion.
Oak powdery mildew, (Erysiphe alphitoides) causes one of the most common diseases of oaks. We assessed the impact of this pathogen on photosynthesis and water relations of infected leaves using ...greenhouse-grown oak seedlings. Transpiration of seedlings infected by oak powdery mildew was also investigated. Altogether, E. alphitoides had a low impact on host gas exchange whether at the leaf or whole plant scale. Maximal stomatal conductance of infected leaves was reduced by 20-30% compared to healthy controls. Severely infected seedlings did not experience any detectable change of whole plant transpiration. The reduction in net CO₂ assimilation, An, was less than proportional to the fraction of leaf area infected. Powdery mildew reduced both the maximal light-driven electron flux (Jmax) and the apparent maximal carboxylation velocity (Vcmax) although Vcmax was slightly more impacted than Jmax. No compensation for the infection occurred in healthy leaves of partly infected seedlings as the reduced photosynthesis in the infected leaves was not paralleled by increased An levels in the healthy leaves of the seedlings. However, E. alphitoides had a strong impact on the leaf life-span of infected leaves. It is concluded that the moderate effect of E. alphitoides on oak might be related to the small impact on net CO₂ assimilation rates and on tree transpiration; nevertheless, the severe reduction in leaf life-span of heavily infected leaves may lead to decreased carbon uptake over the growth season.
The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether ...photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V cmax, and maximal light driven electron flux, J max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A-C i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A opt), V cmax and J max at a reference temperature of 25°C (V cmax₂₅ and J max₂₅) as well as activation energy of V cmax and J max (E aV and E aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V cmax and J max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J max₂₅/V cmax₂₅ was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V cmax₂₅/N a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.
Poplar is the first forest tree genome to be decoded. As an initial step to the comprehensive analysis of poplar proteome, we described reference 2‐D‐maps for eight tissues/organs of the plant, and ...the functional characterization of some proteins. A total of 398 proteins were excised from the gels. About 91.2% were identified by nanospray LC‐MS/MS, based on comparison with 260 000 Populus sp. ESTs. In comparison, reliable PMFs were obtained for only 51% of the spots by MALDI‐TOF‐MS, from which 43% (83 spots) positively matched gene models of the Populus trichocarpa genome sequence. Among these 83 spots, 58% matched with the same proteins as identified by LC‐MS/MS, 21.7% with unknown function proteins and 19.3% with completely different functions. In the second phase, we studied the effect of drought stress on poplar root and leaf proteomes. The function of up‐ and down‐regulated proteins is discussed with respect to the physiological response of the plants and compared with transcriptomic data. Some important clues regarding the way poplar copes with water deficit were revealed.
The responses of Quercus robur (oak) and Fagus sylvatica (beech) seedlings to four different light environments (full, 50%, 40% and 15% sunlight) and to a rapid increase in irradiance were explored ...during the summer, after 2 years of growth in a forest nursery at Nancy (France). Significant differences between the two species were found for most variables. Phenotypic plasticity for morphological variables (root-shoot ratio, leaf size, leaf weight ratio) was higher in beech than in oak, while the reverse was true for anatomical (stomatal density, epidermis thickness, exchange surface area of the palisade parenchyma) and physiological (maximum photosynthetic rate, stomatal conductance, Rubisco activity) variables. Predawn photochemical efficiency (F ^sub v^/F ^sub m^) was higher in oak than in beech in all light environments except in 15% sunlight. F ^sub v^/F ^sub m^was significantly lower in 100% sunlight than in the other light environments in beech but not in oak. Maximum photosynthetic rates (A ^sub max^) increased with increasing light availability in the two species but they were always higher in oak than in beech. Oak exhibited higher Rubisco activity than beech in full sunlight. The transfer of shade-adapted seedlings to the open caused a decrease of F ^sub v^/F ^sub m^, which was larger for beech than for oak. Transferred oak but not beech plants recovered gradually to the control F ^sub v^/F ^sub m^ values. The decreased chlorophyll content and the increased non-photochemical quenching observed in high-light beech seedlings were not enough to avoid photoinhibition. The results suggest that a greater tolerance of strong irradiance is linked to an enhanced physiological plasticity (variables related to photosynthesis), while shade tolerance relies on an enhanced plasticity in light-harvesting variables (crown morphology and chlorophyll content).PUBLICATION ABSTRACT
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