Local Adaptation Drives Leaf Thermoregulation in Tropical Rainforest Trees

Area of Science:

• Ecology
• Plant Physiology
• Climate Change Biology

Background:

• Tropical forests are vital for global biodiversity and climate regulation but face threats from heatwaves and droughts.
• Species vulnerability to rising temperatures can differ due to phenotypic variation, impacting their ability to survive.
• Limited homeothermy, where leaf traits help avoid heat damage, is a potential strategy, but evidence and the roles of acclimation versus adaptation are scarce.

Purpose of the Study:

• To investigate leaf trait variation, photosynthetic heat tolerance, and thermal safety margins in three rainforest tree species across a thermal gradient.
• To assess the capacity for limited homeothermy and differentiate between acclimation and adaptive divergence in response to warming.
• To identify genomic signals of selection related to climate variables and validate findings through controlled experiments.

Main Methods:

• Measured leaf thermal traits and photosynthetic heat tolerance in field populations across a natural temperature gradient.
• Employed a leaf energy balance model to predict leaf-to-air temperature differences (∆T_trait) and thermal safety margins.
• Utilized individual-based genome-wide data to detect adaptive divergence and conducted glasshouse trials to test acclimation responses.

Main Results:

• Intraspecific trait variation reduced ∆T_trait and enhanced heat tolerance in warmer sites for two of the three species, indicating effective buffering.
• Species with greater capacity for heat tolerance and avoidance showed less decline in thermal safety margins with increasing temperature.
• Genomic analyses revealed signals of selection related to temperature and moisture in all species, with experimental validation in one species.

Conclusions:

• Limited homeothermy is evident, with climate gradients driving selection for trait combinations that lower leaf temperatures in warmer-adapted populations.
• Acclimation can adjust individual traits, but their coordinated response maintains specific ∆T_trait under varying conditions.
• Species lacking robust acclimation or adaptive strategies to adjust thermal safety margins face higher extinction risks in a rapidly changing climate.