Divergence of vessel diameter explains interspecific variation in hydraulic safety to salinity in the Sundarbans mangrove ecosystem

Abstract Despite their crucial role in providing ecosystem services and livelihood support in 124 countries, mangroves are facing challenges from warming, altered seasonal precipitation and sea level rise (SLR) in the face of climate change. Variation in intra‐ and interspecific hydraulic traits and related xylem anatomy may allow trees to adapt to changing environmental conditions, yet little is known about adaptive plasticity in mangroves. We examined (i) xylem and hydraulic trait variation across three (low, medium and high) salinity zones in three widespread mangrove species ( Exocecaria agallocha , Xylocarpus moluccensis and Heritiera fomes ) with distinct shade tolerance characteristics in the Bangladesh Sundarbans, (ii) associations of xylem and hydraulic traits, and (iii) habitat (regulator, resource and forest structure) effects on vessel diameter due to its strong influence on hydraulic conductivity variation. Although potential conductivity (K P ) and leaf‐specific conductivity (K L ) showed species‐specific variation, a notably greater conductivity was found in the low‐salinity zone (LSZ), which had lower vessel wall reinforcement (t/b) 2 . Xylem and hydraulic traits exhibited mostly strong phylogenetic signals, whereas pairwise relationships between traits were phylogenetically independent. The study species had distinct hydraulic characteristics, where vessel diameter ( D ) was strongly related to the variation in K P and K L . Furthermore, the study species exhibited a weak trade‐off between hydraulic efficiency and safety. A greater percentage of smaller vessel diameters in light‐demanding E. agallocha indicates greater hydraulic safety against cavitation under stressful conditions than in shade‐tolerant H. fomes , followed by X. moluccensis . Although species characteristics place broad bounds on xylem traits, the combined effects of salinity, nutrient availability and tree size modulate vessel diameter, which leads to hydraulic conductivity variation. The contrasting safety in terms of vessel diameter in mangroves suggests an important role in adaptation to salinity and species distribution. The results also provide insight into salinity‐induced growth reduction and mortality in mangroves. Read the free Plain Language Summary for this article on the Journal blog.