Hydraulic traits explain differential responses of Amazonian forests to the 2015 El Niño‐induced drought

Abstract

Summary Reducing uncertainties in the response of tropical forests to global change requires understanding how intra‐ and interannual climatic variability selects for different species, community functional composition and ecosystem functioning, so that the response to climatic events of differing frequency and severity can be predicted. Here we present an extensive dataset of hydraulic traits of dominant species in two tropical Amazon forests with contrasting precipitation regimes – low seasonality forest (LSF) and high seasonality forest (HSF) – and relate them to community and ecosystem response to the El Niño–Southern Oscillation (ENSO) of 2015. Hydraulic traits indicated higher drought tolerance in the HSF than in the LSF. Despite more intense drought and lower plant water potentials in HSF during the 2015‐ENSO, greater xylem embolism resistance maintained similar hydraulic safety margin as in LSF. This likely explains how ecosystem‐scale whole‐forest canopy conductance at HSF maintained a similar response to atmospheric drought as at LSF, despite their water transport systems operating at different water potentials. Our results indicate that contrasting precipitation regimes (at seasonal and interannual time scales) select for assemblies of hydraulic traits and taxa at the community level, which may have a significant role in modulating forest drought response at ecosystem scales.

Amazonia trees have limited capacity to acclimate plant hydraulic properties in response to long‐term drought

“…Forest resistance and resilience to drought are likely to be mediated by medium and long‐term precipitation variability (Barros et al, ; Ciemer et al, ), which themselves influence species distribution patterns at different scales across the Amazon (Esquivel‐Muelbert et al, ). Our study site, like much of Amazônia, experiences relatively small seasonal changes in water availability (Fisher, Williams, Lourdes Ruivo, Costa, & Meir, ) and it is possible that species in this region have not evolved significant organ‐level plasticity in response to variability in moisture stress.…”

The Pneumatron: An automated pneumatic apparatus for estimating xylem vulnerability to embolism at high temporal resolution

“…Consequently, the current applications of embolism resistance data remain limited. For example, we are far from using it as a trait to select drought tolerant genotypes, to predict how drought may affect trees at the population level and assembly processes for species-rich communities (see Oliveira et al 2019;Barros et al, 2019).…”

Disentangling the effects of environment and ontogeny on tree functional dimensions for congeneric species in tropical forests

“…Tropical tree distribution is strongly shaped by spatiotemporal variation in water availability (Engelbrecht et al , ; Bartlett et al , ; Esquivel‐Muelbert et al , ), but we are still lacking detailed information on the physiological response to drought for the vast majority of tropical tree species because of time and resource constraints (Anderegg et al , ). A pressing challenge for ecologists is to evaluate the potential for relatively easy‐to‐measure traits to capture essential features of tropical tree physiology (O'Brien et al , ; Santiago et al , ; Maréchaux et al , ; Barros et al , ).…”