Patterns and drivers of leaf thermoregulation in rainforest trees of the Australian Wet Tropics

Rising global temperatures are challenging the physiological limits of tropical rainforests. However, trees can exhibit resilience to warming through a combination of increased heat tolerance as well as thermoregulation strategies that maintain leaf temperatures within safe operating margins. These strategies are determined by variation in traits that ultimately affect leaf energy balance. Yet, evidence of this thermoregulatory ability within a species and the relative roles of plasticity and genetic variation remains limited. In this study, experimental and field-based approaches were combined with leaf energy balance modeling to explore the role of intraspecific trait variation in mediating leaf thermoregulation in tropical forests. Across their distribution all target species exhibited levels of intraspecific trait variation indicative of acclimation and/or selection. However, temperature was only a strong driver of this variation in two of the three species. A combination of higher heat tolerance and enhanced leaf cooling in warmer sites effectively increased thermal safety margins by 3°C, compared to species that showed no thermoregulation. These results highlight the importance of considering intraspecific trait variation when assessing tree vulnerability to heat stress.

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