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There is huge uncertainty about how global exchanges of carbon between the atmosphere and land will respond to continuing environmental change. A better representation of photosynthetic capacity is required for Earth System models to simulate carbon assimilation reliably. Here we use a global leaf-trait dataset to test whether photosynthetic capacity is quantitatively predictable from climate, based on optimality principles; and to explore how this prediction is modified by soil properties, including indices of nitrogen and phosphorus availability, measured in situ. The maximum rate of carboxylation standardized to 25 °C (Vcmax25) was found to be proportional to growing-season irradiance, and to increase—as predicted—towards both colder and drier climates. Individual species' departures from predicted Vcmax25 covaried with area-based leaf nitrogen (Narea) but community-mean Vcmax25 was unrelated to Narea, which in turn was unrelated to the soil C:N ratio. In contrast, leaves with low area-based phosphorus (Parea) had low Vcmax25 (both between and within communities), and Parea increased with total soil P. These findings do not support the assumption, adopted in some ecosystem and Earth System models, that leaf-level photosynthetic capacity depends on soil N supply. They do, however, support a previously-noted relationship between photosynthesis and soil P supply. Yunke Peng et al. use in-situ measurements and leaf trait data at 266 global sites for 1637 species and find that the maximum rate of carboxylation standardized to 25 °C is proportional to growing-season irradiance, and covaries with area-based leaf nitrogen and area-based phosphorus on the species level. These results challenge the assumption that leaf-level photosynthetic capacity depends on soil N supply yet supports the relationship between photosynthesis and soil P supply. [ABSTRACT FROM AUTHOR]

Summary: Several publications have examined leaf‐trait and carbon‐cycling shifts along an Amazon–Andes transect spanning 3.5 km in elevation and 16°C in mean annual temperature. Photosynthetic capacity was previously shown to increase as temperature declines with increasing elevation, counteracting enzyme‐kinetic effects. Primary production declines, nonetheless, due to decreasing light availability. We aimed to predict leaf‐trait and production gradients from first principles, using published data to test an emerging theory whereby photosynthetic traits and primary production depend on optimal acclimation and/or adaptation to environment.We re‐analysed published data for 210 species at 25 sites, fitting linear relationships to elevation for both predicted and observed photosynthetic traits and primary production.Declining leaf‐internal/ambient CO2 ratio (χ) and increasing carboxylation (Vcmax) and electron‐transport (Jmax) capacities with increasing elevation were predicted. Increases in leaf nitrogen content with elevation were explained by increasing Vcmax and leaf mass‐per‐area. Leaf and soil phosphorus covaried, but after controlling for elevation, no nutrient metric accounted for any additional variance in photosynthetic traits. Primary production was predicted to decline with elevation.This analysis unifies leaf and ecosystem observations in a common theoretical framework. The insensitivity of primary production to temperature is shown to emerge as a consequence of the optimisation of photosynthetic traits. [ABSTRACT FROM AUTHOR]

Summary: The ratio of leaf intercellular to ambient CO2 (χ) is modulated by stomatal conductance (gs). These quantities link carbon (C) assimilation with transpiration, and along with photosynthetic capacities (Vcmax and Jmax) are required to model terrestrial C uptake. We use optimization criteria based on the growth environment to generate predicted values of photosynthetic and water‐use efficiency traits and test these against a unique dataset.Leaf gas‐exchange parameters and carbon isotope discrimination were analysed in relation to local climate across a continental network of study sites. Sun‐exposed leaves of 50 species at seven sites were measured in contrasting seasons.Values of χ predicted from growth temperature and vapour pressure deficit were closely correlated to ratios derived from C isotope (δ13C) measurements. Correlations were stronger in the growing season. Predicted values of photosynthetic traits, including carboxylation capacity (Vcmax), derived from δ13C, growth temperature and solar radiation, showed meaningful agreement with inferred values derived from gas‐exchange measurements. Between‐site differences in water‐use efficiency were, however, only weakly linked to the plant's growth environment and did not show seasonal variation.These results support the general hypothesis that many key parameters required by Earth system models are adaptive and predictable from plants' growth environments. [ABSTRACT FROM AUTHOR]

Abstract: Plant species show considerable leaf trait variability that should be accounted for in dynamic global vegetation models (DGVMs). In particular, differences in the acclimation of leaf traits during periods more and less favourable to growth have rarely been examined. We conducted a field study of leaf trait variation at seven sites spanning a range of climates and latitudes across the Australian continent; 80 native plant species were included. We measured key traits associated with leaf structure, chemistry and metabolism during the favourable and unfavourable growing seasons. Leaf traits differed widely in the degree of seasonal variation displayed. Leaf mass per unit area (Ma) showed none. At the other extreme, seasonal variation accounted for nearly a third of total variability in dark respiration (Rdark). At the non‐tropical sites, carboxylation capacity (Vcmax) at the prevailing growth temperature was typically higher in summer than in winter. When Vcmax was normalized to a common reference temperature (25°C), however, the opposite pattern was observed for about 30% of the species. This suggests that metabolic acclimation is possible, but far from universal. Intraspecific variation—combining measurements of individual plants repeated at contrasting seasons, different leaves from the same individual, and multiple conspecific plants at a given site—dominated total variation for leaf metabolic traits Vcmax and Rdark. By contrast, site location was the major source of variation (53%) for Ma. Interspecific trait variation ranged from only 13% of total variation for Vcmax up to 43% for nitrogen content per unit leaf area. These findings do not support a common practice in DGVMs of assigning fixed leaf trait values to plant functional types. Trait‐based models should allow for interspecific differences, together with spatial and temporal plasticity in leaf structural, chemical and metabolic traits. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Ecosystem models commonly assume that key photosynthetic traits, such as carboxylation-capacity measured at a standard temperature, are constant in time. The temperature responses of modelled photosynthetic/respiratory rates then depend entirely on enzyme kinetics. Optimality considerations suggest this assumption may be incorrect. The 'co-ordination hypothesis' (that Rubisco- and electron-transport limited rates of photosynthesis are co-limiting under typical daytime conditions) predicts instead that carboxylation (Vcmax) and light-harvesting (Jmax) capacities, and mitochondrial respiration in the dark (Rdark), should acclimate so that they increase with growth temperature - but less steeply than their instantaneous response rates. To explore this hypothesis, photosynthetic measurements were carried out on woody species during the warm and the cool seasons in the semi-arid Great Western Woodlands, Australia, under broadly similar light environments. A consistent linear relationship between Vcmax and Jmax was found across species. Vcmax, Jmax and Rdark increased with temperature, but values standardized to 25 °C declined. The ci:ca ratio increased slightly with temperature. The leaf N:P ratio was lower in the warm season. The slopes of the relationships of log-transformed Vcmax and Jmax to temperature were close to values predicted by the co-ordination hypothesis, but shallower than those predicted by enzyme kinetics. [ABSTRACT FROM AUTHOR]

We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests ( TMFs) in the Andes/western Amazon regions of Peru., We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco ( Vcmax), and the maximum rate of electron transport ( Jmax)), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area ( Ma, Na and Pa, respectively), and chlorophyll from 210 species at 18 field sites along a 3300-m elevation gradient. Western blots were used to quantify the abundance of the CO2-fixing enzyme Rubisco., Area- and N-based rates of photosynthetic capacity at 25°C were higher in upland than lowland TMFs, underpinned by greater investment of N in photosynthesis in high-elevation trees. Soil [P] and leaf Pa were key explanatory factors for models of area-based Vcmax and Jmax but did not account for variations in photosynthetic N-use efficiency. At any given Na and Pa, the fraction of N allocated to photosynthesis was higher in upland than lowland species. For a small subset of lowland TMF trees examined, a substantial fraction of Rubisco was inactive., These results highlight the importance of soil- and leaf-P in defining the photosynthetic capacity of TMFs, with variations in N allocation and Rubisco activation state further influencing photosynthetic rates and N-use efficiency of these critically important forests. [ABSTRACT FROM AUTHOR]