Water use efficiency in mangroves: Conservation of water use efficiency determined by stomatal behavior across leaves, plants, and forests

Absorption of water from seawater with its high osmotic pressure is costly to mangroves and requires the plants to use water conservatively. Indeed, measurements of gas exchange, growth rate and carbon isotope composition have shown that mangrove species operate with higher water-use efficiency (WUE) than do most C₃ species. These characteristics of water use and water use efficiency find expression in interspecific differences in salinity tolerance, and in the structure of mangrove forests along complex gradients in salinity and aridity. Under global warming, mangroves face increasing challenges of varying salinity, humidity and temperature, all factors that affect water use and WUE. The extent to which mangroves can acclimate to changing environmental conditions by altering water-use characteristics depends on spatial (leaf, plant, and ecosystem) and temporal (short- and long-term) factors. Here, we clarify concepts of WUE at each spatiotemporal scale, compare their values across scales, and show consistency in maintenance of a high water use efficiency from leaves to ecosystems. We develop a framework for comparison of WUE across scales and identify areas for future research.