Plant Thermoregulation: Energetics, Trait-Environment Interactions, and Carbon Economics

Building a more predictive trait-based ecology requires mechanistic theory based on first principles. We present a general theoretical approach to link traits and climate. We use plant leaves to show how energy budgets (i) provide a foundation for understanding thermoregulation, (ii) explain mechanisms driving trait variation across environmental gradients, and (iii) guide selection on functional traits via carbon economics. Although plants are often considered to be poikilotherms, the data suggest that they are instead limited homeotherms. Leaf functional traits that promote limited homeothermy are adaptive because homeothermy maximizes instantaneous and lifetime carbon gain. This theory provides a process-based foundation for trait-climate analyses and shows that future studies should consider plant (not only air) temperatures. Plants are generally considered to be poikilotherms that do not thermoregulate. However, empirical data show that plants are actually limited homeotherms that do thermoregulate.Plant thermoregulation and limited homeothermy decouples physiological functioning from climatic variation to promote metabolic homeostasis and maximize carbon assimilation and fitness.Energy budgets and carbon economics provide a mechanistic theory for understanding and predicting these relationships. Specifically, theory suggests that thermoregulation evolved via natural selection on traits to maximize lifetime carbon gain, growth, production, and fitness across climate gradients.Future studies need to consider plant tissue (and not only air) temperatures.