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

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Jan 13, 2025 version files 64.09 KB

Abstract

Sundarbans (~10000 sq km), the world’s largest single-block mangrove ecosystem, provides important ecosystem goods and services to > 7.5 million coastal people in two neighboring countries, Bangladesh (~60%) and India (~40%). It has extensive variability in environmental variables, including siltation and salinity, which are influenced by freshwater damming in the north and changing seawater levels from the south. Based on spatial salinity gradients, this ecosystem is divided into three contrasting salinity zones: the low salinity zone (LSZ, eastern and northeastern part), the medium salinity zone (MSZ, central and southern part), and the high salinity zone (HSZ, western and southwestern part). Forest growth, such as tree height, increases from the HSZ to the LSZ and varies between salinity zones. However, human disruptions and rapid environmental changes, such as sea level rise (SLR), pose a threat to this sensitive ecosystem. Increasing salinity creates challenges for hydraulic transport in mangrove species. Therefore, studies on variation in intra- and interspecific hydraulic traits, and associated xylem anatomy may allow us to understand the adaptation of mangrove species to changing environmental conditions. in this study, we examined how xylem and hydraulic traits vary among dominant tree species such as Exocecaria agallocha, Xylocarpus moluccensis, and Heritiera fomes growing under climatically identical but heterogeneous environmental conditions in the Sundarbans. Although potential conductivity (KP) and leaf-specific conductivity (KL) 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 was strongly related to the variation in KP and KL. Furthermore, the study species exhibited a weak trade-off between hydraulic efficiency and safety. A higher frequency of smaller vessel diameters in light-demanding E. agallocha indicates greater hydraulic safety 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 reveals an underlying mechanism of tree growth and species distribution in the Sundarbans.