Vapour pressure deficit modulates hydraulic function and structure of tropical rainforests under nonlimiting soil water supply

Abstract

Summary Atmospheric conditions are expected to become warmer and drier in the future, but little is known about how evaporative demand influences forest structure and function independently from soil moisture availability, and how fast‐response variables (such as canopy water potential and stomatal conductance) may mediate longer‐term changes in forest structure and function in response to climate change. We used two tropical rainforest sites with different temperatures and vapour pressure deficits (VPD), but nonlimiting soil water supply, to assess the impact of evaporative demand on ecophysiological function and forest structure. Common species between sites allowed us to test the extent to which species composition, relative abundance and intraspecific variability contributed to site‐level differences. The highest VPD site had lower midday canopy water potentials, canopy conductance (gc), annual transpiration, forest stature, and biomass, while the transpiration rate was less sensitive to changes in VPD; it also had different height–diameter allometry (accounting for 51% of the difference in biomass between sites) and higher plot‐level wood density. Our findings suggest that increases in VPD, even in the absence of soil water limitation, influence fast‐response variables, such as canopy water potentials and gc, potentially leading to longer‐term changes in forest stature resulting in reductions in biomass.

Woody component of tropical rainforest recovers slower from drought than the upper canopy layer and leaves

“…The strong impact of moisture-related climatic conditions during the recovery period on the recovery of woody component partly depends on the sensitivity of vegetation to speci c climatic factors. For example, VPD modulates hydraulic function and structure in tropical rainforests during the recovery period with su cient soil water supply (Binks et al, 2023), making tall Amazonian forests more sensitive to VPD than precipitation (Giardina et al, 2018). Soil moisture supplies the water resource to tropical forest and thus to be a key controller of tropical forest local hydrology (Bruno et al, 2006).…”