Water Use Characteristics Of Two Sonneratia Mangrove Species

Mangroves are plants growed in tropical and subtropical tidal wetlands.Saline environment is a physiological obstacle for mangroves because water uptake is more energy-consuming under the extremely negative water potential of the seawater.Mangroves have developed very particular water use strategies in order to survive in highly saline and anaerobic environments,often resulting in efficient water use.Water use by trees in such saline environment has always been considered as a key process for understanding the special life traits of mangroves.Herein,we first studied water use characteristics of two mangrove species with same age,Sonneratia apetala and Sonneratia caseolaris,growing in intertidal environments in China,from 2015 to 2016,using sap flow machine and meteorological station.We also investigated how the chilling injury event influenced water use characteristics of S.apetala and S.caseolaris.We investigated radial patterns of sap flow densities of S.apetala and S.caseolaris and tried to explain it with anatomical characteristics.We estimated carbon uptake of S.apetala and S.caseolaris using sap flow measurements and stable carbon isotope discrimination.Main results and conclusions are listed below.1.Whole-tree water use of S.apetala and S.caseolaris was relatively conservative compared to terrestrial tree species.In contrast,water use of them represents the higher end of what has been reported in the literature in comparison with mangroves species.S.apetala had the higher whole tree water use than S.caseolaris,which may explain why S.apetala might be more competitive along the Chinese coast and indicating that S,apetala had a greater influence on local area water budget than S.caseolaris.There was no significant difference in gross primary production between S.apetala and S.caseolaris plantations.2.There were strong relationship among meteorological factors and sap flow densities of S.apetala and S.caseolaris,including photosynthetically active radiation,atmospheric temperature,soil temperature,vapor pressure deficit and relative humidity.Chilling injury changed how sap flow densities of S.apetala and S.caseolaris responsed to photosynthetically active radiation and caused a higher leaf loss in S.caseolaris than in S.apetala and a significant decline of water uptake in S.caseolaris.3.Higher radial resistance in sapwood of S.caseolaris caused a steeper decline of sap flow density radially in S.caseolaris than in S.apetala.Futhermore,S.apetala had more percentage of sapwood area remained hydro-active than S.caseolaris which may indicated that S.apetala had a better water use regime than S.caseolari.Results showed that about 55%and 51%of water use could be overestimated if acute radial reductions in sap flow were not considered,corresponding to average discrepancies in stand water use of 5.6 mm d-1 for S.apetala and 2.5 mm d-1 for S.caseolaris.