Decoupled phenology and PSII thermal plasticity in seasonally dry tropical forest trees

We tested whether seasonal plasticity in photosystem II (PSII) heat tolerance aligns with leaf phenology in tropical trees, comparing evergreen and deciduous species across the wet⍰to⍰post⍰wet transition in a seasonally dry tropical forest of the central Western Ghats, India. This transition, preceding drought⍰induced senescence, represents the key window to assess true unstressed thermal plasticity. PSII thermal traits: damage onset ( T ₅ ), damage midpoint ( T ₅₀ ), and temperature between damage onset to full loss ( T ₉₅ – T ₅ ), decline width (DW) were quantified in 27 co⍰occurring species during the wet (27.5□°C) and post⍰wet (31.6□°C) periods. Contrary to phenology⍰based predictions, PSII plasticity was not structured by leaf habit or successional status. Both T ₅ (+1.7□°C) and T ₅₀ (+0.9□°C) increased significantly across seasons, but responses were species⍰specific, with evergreen and deciduous trees acclimating similarly. The prevention⍰versus⍰forbearance trade⍰off ( T ₅ – DW relationship) remained conserved, though leaf habits diverged under post⍰wet conditions. Thermal safety margins based on T ₅₀ were large, but T ₅ revealed vulnerable late⍰successional evergreens ( Saraca asoca, Ficus spp.) and Careya arborea . These results show that PSII thermotolerance regulation operates largely independently of drought⍰avoidance phenology, indicating species identity and not leaf habit drives plasticity in PSII thermal response in seasonally dry tropical forests.