Absorption of Energy in Excess, Photoinhibition, Transpiration, and Foliar Heat Emission Feedback Loops During Global Warming

Abstract

Highlights: What are the main findings? Foliar temperature response during excess light stress is the result of a dynamic interplay between NPQ, qE, photochemistry, and transpiration rather than of any single mechanism. Thus, spatial and temporal heterogeneity of leaf temperature arises from the physiological state and absorbed energy fate balance. Conditionally, the ratio between these processes can vary, thus increasing or decreasing foliar heat emission and warming up or cooling down the surrounding environment. Constraints imposed by global warming and drought can further disrupt this balance, increasing the risk of foliar heat stress and cell death induction. What are the implications of the main finding? Leaf-internal energy redistribution represents an important but often simplified and ignored component of foliar thermoregulation under excess light and climate warming. Explicit consideration of these interactions may improve understanding and modelling of plant–climate feedbacks under future warming scenarios. Global warming is increasingly constraining plant productivity by altering the photosynthetic energy balance and leaf thermoregulation. Under high light and elevated temperatures, absorption of energy in excess (AEE) by photosystem II disrupts photosynthetic electron transport, oxygen evolution, and CO2 assimilation, often accompanied by reduced foliar transpiration. These conditions promote photoinhibition, as reflected by a decrease in maximal photosynthetic efficiency (Fv/Fm), an increase in non-photochemical quenching (NPQ), and photooxidative stress associated with enhanced reactive oxygen species (ROS) production. In addition to environmental heat stress, AEE influences foliar temperature through internal energy partitioning, including regulated dissipation of AEE as heat and changes in transpirational cooling. The relative contributions of NPQ, photochemistry, and transpiration to leaf temperature regulation are strongly context dependent and vary with light intensity, temperature changes, and water availability. Under global warming, rising background temperatures and increased vapor pressure deficit may constrain transpirational cooling and alter the balance between non-photochemical and photochemical energy dissipation and usage, respectively. In this review, we synthesize current knowledge on AEE handling, photoinhibition, NPQ and other quenching processes, and on transpiration cooling, and discuss a conceptual framework in which sustained imbalance among these processes under global warming conditions could amplify foliar heat stress and increase the risk of cellular damage. Rather than proposing new physiological mechanisms, this work integrates existing evidence across molecular, leaf, and ecosystem scales to highlight potential feedbacks relevant to plant performance under future climate prediction scenarios.