Water use in mangroves: Understanding how wood day capacitance varies under salinity in the Sundarbans

Mangroves are carbon-rich ecosystems that offer vital goods and services, particularly acting as a barrier to natural disasters, such as storms and tidal surges. However, mangroves around the world are experiencing increasing salinity stress due to global change, such as sea level rise, altered precipitation patterns, and increasing temperature. Wood day capacitance (WDC)−the temporary water release from wood to sustain hydraulic supply for carbon assimilation and transpiration−influences daily water use and tree growth under hydraulic stress. Although understanding species-specific WDC variation along environmental gradients is important to predict how species could adapt under increasing environmental stress, such knowledge is limited for mangroves. Here, we examine (i) how WDC and physiological variables (e.g., leaf water potential) vary in two dominant mangrove species (Exocecaria agallocha and Heritiera fomes) across three (low, medium, and high) salinity zones in the Bangladesh Sundarbans and (ii) how ecophysiological variables and wood density influence WDC variation. Our results reveal that (i) in less-stressed habitats (i.e., low salinity zone), both species exhibit higher WDC and cumulative water release (CWR) with less negative leaf water potential that enable them to maintain hydraulic functions under variable salinity conditions; (ii) compared to shade tolerant H. fomes, light demanding E. agallocha has higher WDC and low wood density that help in rapid resource acquisition, and (iii) salinity modulates WDC to buffer water stress, an adaptation strategy to avoid water deficits. The results suggest that WDC contributes to the diurnal water balance in mangroves in relation to environmental change.