Australia-wide photosynthetic trait dataset

"Least-cost theory" posits that C3 plants should balance rates of photosynthetic water loss and carboxylation in relation to the relative acquisition and maintenance costs of resources required for these activities. Here we investigated the dependency of photosynthetic traits on climate and soil properties using a new Australia-wide trait dataset spanning 528 species from 67 sites. We tested the hypotheses that plants on relatively cold or dry sites, or on relatively more fertile sites, would typically operate at greater CO2 drawdown (lower ratio of leaf internal to ambient CO2, Ci:Ca) during light-saturated photosynthesis, and at higher leaf N per area (Narea) and higher carboxylation capacity (Vcmax 25) for a given rate of stomatal conductance to water, gsw. These results would be indicative of plants having relatively higher water costs than nutrient costs. In general, our hypotheses were supported. Soil total phosphorus (P) concentration and (more weakly) soil pH exerted positive effects on the Narea-gsw and Vcmax 25-gsw slopes, and negative effects on Ci:Ca. The P effect strengthened when the effect of climate was removed via partial regression. We observed similar trends with increasing soil cation exchange capacity and clay content, which affect soil nutrient availability, and found that soil properties explained similar amounts of variation in the focal traits as climate did. Although climate typically explained more trait variation than soil did, together they explained up to 52% of variation in the slope relationships and soil properties explained up to 30% of the variation in individual traits. Soils influenced photosynthetic traits as well as their coordination. In particular, the influence of soil P likely reflects Australia's geologically ancient low-relief landscapes with highly leached soils. Least-cost theory provides a valuable framework for understanding trade-offs between resource costs and use in plants, including limiting soil nutrients.Microsoft ExcelFunding provided by: Hermon Slade FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001109Award Number: Funding provided by: Australian Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000923Award Number: Funding provided by: Natural Sciences and Engineering Research Council of CanadaCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000038Award Number: Funding provided by: European Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010663Award Number:Data collection/generation of data: Light-saturated rates of photosynthesis were measured at ambient CO2 levels using a portable gas exchange system. Stomatal conductance to water vapor and Ci:Ca correspond to light-saturated rates of photosynthesis. Carboxylation capacity, Vcmax, was estimated via the one-point method when it was not provided from A-ci curves. Concentrations of leaf nitrogen and phosphorus were measured using an elemental analyzer. LMA was measured by dividing the leaf dry mass by the surface area of a fresh leaf. Climate data were extracted for each site from the eMAST data project. Soil data were measured for a subset of sites and extracted from the CSIRO SoilGrids for the remaining sites. Data processing: Raw data were used to calculate species means for all sites, which were then compiled to produce one data file. This was done using RStudio Version 1.3.959. Environmental/experimental conditions: All data were collected on native plant species growing under natural conditions in the field. Describe any quality-assurance procedures performed on the data: Ci:Ca values less than 0 or greater than 1 were excluded, as were stomatal conductance values greater than 3000 millimol per square meter per second. Vcmax 25 values greater than 500 micromol CO2 per square meter per second were also excluded from the final analysis