The rise of trait-based ecology has led to an increased focus on the distribution and dynamics of traits across broad geographic and climatic gradients. A central focus is how the trait composition of plant communities influences ecosystem function. However, a general theory of trait-based ecology that applies across scales and geographic and climatic gradients has yet to be formulated. A key challenge for predicting ecosystem functioning is linking shifts in climate, plant functional composition, and soil microbial diversity and functioning. Variation in leaf functional traits across climate gradients may originate from natural selection to maintain leaf temperatures near metabolic optima and increase growth efficiencies to compensate for variation in temperature. Under this hypothesis, climate drives variation in functional traits of leaves and the microbes that consume them. In this talk, we integrate several separate theories including the adaptive trait continuum hypothesis, trait-drivers theory, and energy budget theory to generate novel predictions for the links between climate, leaf functional traits, and microbial functional traits.
Our results show that leaf and microbial traits are strongly correlated with climate and with each other. These coordinated shifts in function are important, as previous studies have shown that plant and microbial diversity are differentially influenced by climate. Our theory predicts that shifts in climate will drive variation in a suite of leaf traits in order to maintain leaf operating temperatures and maximize net carbon assimilation and whole-plant growth rates. These predictions appear to be supported by globally distributed data for leaf thermal and photosynthetic traits. Our results demonstrate that the temperatures of plant tissues drive shifts in plant functional traits across broad climate gradients and that these shifts in plant function ramify to influence microbial communities.