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.

最小成本理论（Least-cost theory）提出，C3植物需要平衡光合水分损失与羧化作用的速率，以匹配这些生理过程所需资源的相对获取与维持成本。本研究依托一套全新的全澳范围性状数据集，该数据集涵盖来自67个样地的528个物种，探究了光合性状对气候与土壤属性的依赖性。我们验证了如下假说：在相对寒冷、干旱或肥力较高的样地中，植物在光饱和光合过程中通常会维持更高的CO₂下降幅度（即更低的叶片胞内与环境CO₂比值Ci:Ca），且在特定气孔导度（gsw）下，具备更高的单位叶面积氮含量（Narea）与羧化能力（Vcmax 25）。这类结果可反映出植物具有相对更高的水分成本而非养分成本。总体而言，我们的假说得到了支持。土壤全磷（P）含量以及影响相对较弱的土壤pH值，对Narea-gsw与Vcmax 25-gsw的斜率产生正向影响，同时对Ci:Ca产生负向影响。通过偏回归分析剔除气候的影响后，磷元素的效应会增强。我们还观察到，随着影响土壤养分有效性的土壤阳离子交换量与黏粒含量升高，也呈现出类似趋势；并且发现土壤属性对目标性状变异的解释度与气候相当。尽管气候对性状变异的解释度通常高于土壤，但二者联合可解释高达52%的斜率关系变异，而土壤属性可单独解释高达30%的单个性状变异。土壤不仅会影响光合性状，还会影响其协调关系。具体而言，土壤磷的影响或反映了澳大利亚地质古老、地势平缓且土壤高度淋溶的景观特征。最小成本理论为理解植物资源成本与利用之间的权衡（包括受土壤养分限制的情况）提供了极具价值的分析框架。