Leaf temperature and its departure from ambient air temperature

Area of Science:

• Plant physiology
• Ecology
• Climate science

Background:

• Leaf temperature (Tl) influences carbon and water exchange, regulated by microclimate and plant traits.
• The relationship between leaf temperature and air temperature (Tl-Ta) is key for assessing plant thermoregulation.
• Global observations reveal thermoregulation patterns are strongly linked to temperature gradients.

Purpose of the Study:

• To synthesize global observations of the leaf temperature-air temperature relationship across diverse climates and biomes.
• To identify how plant thermoregulation strategies vary with environmental temperature.
• To highlight the need for improved stomatal theories incorporating thermal regulation.

Main Methods:

• Global synthesis of ground and satellite thermal measurements.
• Analysis of the leaf temperature-air temperature (Tl-Ta) relationship across different biomes and climates.
• Examination of thermoregulation patterns, including megathermy, homeothermy, and poikilothermy.

Main Results:

• Thermoregulation patterns predominantly vary along temperature gradients.
• Megathermy (dTl/dTa > 1) is common in warm tropics and sun-exposed leaves due to heat accumulation.
• Limited homeothermy (dTl/dTa < 1) and poikilothermy (dTl/dTa = 1) are prevalent in cold regions or shaded leaves.
• Stomatal control can mitigate rapid leaf temperature increases under heat stress, but exceeding critical thresholds leads to non-linear temperature rises.

Conclusions:

• Plant thermoregulation is strongly influenced by ambient temperature and solar radiation exposure.
• Current mechanistic models may overestimate photosynthetic rates due to a lack of thermal regulation in stomatal models.
• Developing new stomatal theories optimizing carbon gain, water loss, and thermal regulation is crucial for accurate plant modeling.