Divergent hydraulic responses to dry season water limitation for canopy dominant species in an Eastern Amazon Rainforest

Abstract:

Estimation of plant water fluxes and hydraulic state under conditions of water limitation are paramount to understanding functional controls on forest water cycling. Traditional methods of assessing this response include continuous measurements of sap flow velocity and either discrete or continuous measurements of plant water potential (leaf or stem). Thermometric methods of estimating sap flow velocity are dependent on internal properties such as wood anatomy and tissue moisture content. While these dependencies create challenges for accurate estimation of water fluxes, they also contain information about overall water function and the hydraulic state of the system. In this work, we synthesize ecophysiological and continuous measurements from trees located in a highly seasonal Amazon rainforest (Tapajós National Forest, Pará, Brazil) to examine the interactions between dry season dynamics and plant hydraulic state measured via different pathways. The abnormally dry 2015-2016 El Niño dry season resulted in divergence of daily stem water potential and water usage between canopy individuals, hinting at an array of water limitation responses across canopy dominant species. We further compared estimated changes in stem moisture content to daily stem water potential, inferring a system-scale relationship between changes in relative water content and water potential. Results suggest that this system scale relationship may act as a potential proxy for translation between water potential and relative water content across multiple individuals.