Nocturnal Sap Flow as Compensation for Water Deficits: An Implicit Water-saving Strategy Used by Mangroves in Stressful Environments

Abstract

As part of the plant water-use process, plant nocturnal sap flow ( Q) 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. The Q existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow ( Q) across species, which was associated with two processes, nocturnal transpiration ( E) and nocturnal stem water refilling ( R). The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in Q/ Q among species. For Kandelia obovata and Aegiceras corniculatum, R was the main contributor to Q, which driven by the demands of stem water refilling after diurnal water depletion and high salinity. In contrast, Avicennia marina maintained a low Q, driven by vapor pressure deficit, and the Q mainly used for E, which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways Q properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.