AUTHOR=Wu Sipan , Gu Xiaoxuan , Zheng Yanghang , Chen Luzhen 

TITLE=Nocturnal sap flow as compensation for water deficits: an implicit water-saving strategy used by mangroves in stressful environments

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1118970

DOI=10.3389/fpls.2023.1118970

ISSN=1664-462X

ABSTRACT=<p>As part of the plant water-use process, plant nocturnal sap flow (<italic>Q</italic><sub>n</sub>) has been demonstrated to have important ecophysiological significance to compensate for water loss. The purpose of this study was to explore nocturnal water-use strategies to fill the knowledge gap in mangroves, by measuring three species co-occurring in a subtropical estuary. Sap flow was monitored over an entire year using thermal diffusive probes. Stem diameter and leaf-level gas exchange were measured in summer. The data were used to explore the different nocturnal water balance maintaining mechanisms among species. The <italic>Q</italic><sub>n</sub> existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow (<italic>Q</italic>) across species, which was associated with two processes, nocturnal transpiration (<italic>E</italic><sub>n</sub>) and nocturnal stem water refilling (<italic>R</italic><sub>n</sub>). We found that the stem recharge of the <italic>Kandelia obovata</italic> and <italic>Aegiceras corniculatum</italic> occurred mainly after sunset and that the high salinity environment drove higher <italic>Q</italic><sub>n</sub> while stem recharge of the <italic>Avicennia marina</italic> mainly occurred in the daytime and the high salinity environment inhibited the <italic>Q</italic><sub>n</sub>. The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in <italic>Q</italic><sub>n</sub>/<italic>Q</italic> among species. For <italic>Kandelia obovata</italic> and <italic>Aegiceras corniculatum</italic>, <italic>R</italic><sub>n</sub> was the main contributor to <italic>Q</italic><sub>n</sub>, which was driven by the demands of stem water refilling after diurnal water depletion and high salt environment. Both of the species have a strict control over the stomata to reduce water loss at night. In contrast, <italic>Avicennia marina</italic> maintained a low <italic>Q</italic><sub>n</sub>, driven by vapor pressure deficit, and the <italic>Q</italic><sub>n</sub> mainly used for <italic>E</italic><sub>n</sub>, which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways <italic>Q</italic><sub>n</sub> properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.</p>