DOI: 10.5061/dryad.j9kd51cgr
title: Australia-wide photosynthetic trait dataset

description: “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.
description: Data collection/generation of data: Light-saturated rates of
 photosynthesis were measured at ambient CO<sub>2</sub> levels
 using a portable gas exchange system. Stomatal conductance to water vapor
 and C<sub>i</sub>:C<sub>a</sub> correspond to
 light-saturated rates of photosynthesis. Carboxylation capacity,
 V<sub>cmax</sub>, 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:
 C<sub>i</sub>:C<sub>a</sub> values less than 0 or
 greater than 1 were excluded, as were stomatal conductance values greater
 than 3000 millimol per square meter per second.
 V<sub>cmax</sub> 25 values greater than 500 micromol
 CO<sub>2</sub> per square meter per second were also excluded
 from the final analysis.
description: Microsoft Excel