Amazonian trees under long-term drought exposure are more resilient to El Niño extreme

The rising frequency and intensity of extreme droughts across the Amazon raises uncertainty about the capacity of tropical forests to adjust to future climate. Here, we combined the severe 2023 El Niño drought with a multi-decadal throughfall-exclusion experiment to compare eco-physiological resilience between pre-exposed drought-primed trees (PT) and untreated controls (CT). During El Niño, PTs reduced transpiration by 25%, while CTs declined by up to 54% relative to pre-drought levels. Post-drought, PTs fully recovered transpiration, whereas CTs recovered only to 77.5%, showing legacy effects and pronounced leaf area loss. These differences were reinforced by long-term structural changes (i.e., mortality) in the TFE, which reduced water competition during extreme drought. Tree structural data revealed a significantly smaller crown-to-stem size ratio in PTs, reducing sensitivity to evaporative demand and underpinning their enhanced drought resistance and resilience. These findings reveal that physiological resilience to extreme events can emerge from long-term drought exposure through structural adjustments at both ecosystem and individual tree scale.