Hysteresis area at the canopy level during and after a drought event in the Central Amazon

•2015 ENSO led to potential water supply-demand imbalance at canopy level.•In the Amazon forest VPD peaks in the early afternoon.•gs is higher during the morning period to minimize water loss.•Harea effectively quantifies Amazon drought stress.•Harea is shaped by temporal lags between the observed variables. Understanding forest water limitation during droughts within a warming climate is essential for accurate predictions of forest-climate interactions. In hyperdiverse ecosystems like the Amazon forest, the mechanisms shaping hysteresis patterns in transpiration relative to environmental factors are not well understood. From this perspective, we investigated these dynamics by conducting in situ leaf-level measurements throughout and after the 2015 El Niño-Southern Oscillation (ENSO) drought. Our findings indicate a substantial increase in the hysteresis area (Harea) among transpiration (E), vapor pressure deficit (VPD), and stomatal conductance (gs) at canopy level during the ENSO peak, attributed to both temporal lag and differences in magnitude between gs and VPD peaks. Specifically, the canopy species Pouteria anomala exhibited an increased Harea, due to earlier maximum gs rates leading to a greater temporal lag with VPD compared to the post-drought period. Additionally, leaf water potential (ΨL) and canopy temperature (Tcanopy) showed larger Harea during the ENSO peak compared to post-drought conditions across all studied species, suggesting that stomatal closure, particularly during the afternoon, acts to minimize water loss and may explain the counterclockwise hysteresis observed between ΨL and Tcanopy. The pronounced Harea during the drought points to a potential imbalance between water supply and demand, underlining the role of stomatal behavior of isohydric species in response to drought. Canopy-level transpiration during the 2015 ENSO-driven drought in the Central Amazon exhibited significant deviations due to exceptionally high Vapor Pressure Deficit (VPD) conditions and increased temporal differences between the peaks of stomatal conductance (gs) and VPD. This resulted in an increased hysteresis effect, as evidenced by the expanded hysteresis area (Harea) across multiple ecophysiological variables compared to the post-drought period. [Display omitted]