Thresholds for persistent leaf photochemical damage predict plant drought resilience in a tropical rainforest.

Water stress can cause declines in plant function that persist after rehydration. Recent work has defined 'resilience' traits characterizing leaf resistance to persistent damage from drought, but whether these traits predict resilience in whole-plant function is unknown. It is also unknown whether the coordination between resilience and 'resistance' - the ability to maintain function during drought - observed globally occurs within ecosystems. For eight rainforest species, we dehydrated and subsequently rehydrated leaves, and measured water stress thresholds for declines in rehydration capacity and maximum quantum yield of photosystem II (F /F ). We tested correlations with embolism resistance and dry season water potentials (Ψ ), and calculated safety margins for damage (Ψ - thresholds) and tested correlations with drought resilience in sap flow and growth. Ψ thresholds for persistent declines in F /F , indicating resilience, were positively correlated with Ψ and thresholds for leaf vein embolism. Safety margins for persistent declines in F /F , but not rehydration capacity, were positively correlated with drought resilience in sap flow. Correlations between resistance and resilience suggest that species' differences in performance during drought are perpetuated after drought, potentially accelerating shifts in forest composition. Resilience to photochemical damage emerged as a promising functional trait to characterize whole-plant drought resilience.