EXAMINING DAILY AND DRY SEASON CAPACITIVE WATER RELEASE OF AFRICAN TROPICAL TREES IN A CHANGING CLIMATE

Abstract

Tropical forests are vital to the global carbon budget, regional water cycling and biodiversity, but face major threats in a changing climate. Tree die-off due to drought is a concern of increasing magnitude. Understanding how tropical trees manage their water economy under varying environmental conditions is critical for predicting forest resilience during warming and drought. Hydraulic capacitance, the ability of wood tissues to release stored water, plays a key role in buffering short-term water deficits and sustaining physiological function during drought, but is not well understood in tropical trees. In this study, we measured branch wood capacitance at both diurnal (between predawn and midday) and seasonal (between predawn and drought conditions) scales across six tropical tree species planted along an elevation gradient in Rwanda. We investigated how capacitance varies among species and along the climatic gradient, and how it relates to functional traits such as wood density and volumetric water content. It was found that capacitance varies among species and climates, suggesting that it is a trait which can respond to environmental variation, but is ultimately highly dependent on species-specific hydraulic strategies. Capacitance was lowest among all species in the warmest and driest site, while capacitance was similar between the intermediate and wettest and coldest site. We observed indications of correlations between capacitance and volumetric water content and wood density, suggesting that the ability to release water can be dependent on these traits also in tropical trees. Our findings highlight that while capacitance can be functionally important, there is a need to integrate it with information on other physiological and anatomical traits that control tree water uptake, storage and loss to get a more wholistic understanding of tree water economy under heat and drought.