A comparative analysis of photosynthetic recovery from thermal stress: a desert plant case study.

Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (F(V)/F(M)), rarely accounting for the recovery of effective quantum yield (ΔF/F(M')) after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species' thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species' thermal tolerance thresholds (T 50) are related to the ability to recover from short-term heat stress in 41 Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T 50 and recovery capacity were positively correlated, the relationship was weaker for species with high T 50 values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.