Photosystem II Heat Tolerance in Tropical Trees Operates Independently of Leaf Phenology
A study of 27 co-occurring tree species in India's Western Ghats found that photosystem II heat tolerance increases seasonally in both evergreen and deciduous trees, with no meaningful difference between the two groups. The research measured three thermal damage thresholds across the wet and post-wet seasons in a seasonally dry tropical forest, a period preceding drought-induced leaf loss. The findings challenge the assumption that drought-avoidance leaf phenology predicts a tree's capacity to thermally acclimate its photosynthetic machinery.
Researchers tested whether seasonal changes in photosystem II (PSII) heat tolerance—the point at which a tree's photosynthetic apparatus begins to sustain heat damage—track with leaf phenology in tropical trees of the central Western Ghats, India. Across 27 co-occurring species, both the damage onset temperature (T5) and the damage midpoint temperature (T50) increased significantly from the wet to the post-wet season, by approximately 1.7°C and 0.9°C respectively, indicating widespread thermal acclimation. Contrary to predictions, this acclimation was not structured by whether a species was evergreen or deciduous, nor by successional status. Responses were instead species-specific, pointing to species identity as the primary driver of PSII thermal plasticity. While thermal safety margins based on T50 appeared large across the board, the more sensitive damage-onset metric (T5) identified specific late-successional evergreen species—including Saraca asoca, Ficus spp., and Careya arborea—as potentially vulnerable. A trade-off between damage prevention and damage tolerance was conserved across seasons, though the two leaf habit groups showed some divergence under post-wet conditions.
What's missing
The study is a preprint posted to bioRxiv and has not yet undergone peer review, so findings should be interpreted with caution. The authors do not report whether the observed increases in thermotolerance are sufficient to buffer species against projected future temperature increases under climate change scenarios. The geographic scope is limited to a single forest site in the Western Ghats, and it is unclear how generalizable these findings are to other seasonally dry tropical forests globally. The mechanisms driving species-specific plasticity—whether genetic, morphological, or biochemical—are not resolved.
What different sources said
- bioRxivCenter
Decoupled phenology and PSII thermal plasticity in seasonally dry tropical forest trees
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