The Impact Of Invasive Smooth Cordgrass (Spartina Alterniflora Loisel.) On Organic Carbon Stock In Jiuduansha Wetland

In this study,organic carbon pool of exotic Spartina alterniflora(S.alterniflora)and native Scirpus mariqueter(S.mariqueter),and the rate of litter decomposition were researched in Jiuduansha wetlands.The object is to explore the impact of invasive S.alterniflora on carbon storage,further improve our understanding about whether the invasion of S.alterniflora is beneficial to the "carbon sink" function of Jiuduansha wetland s.Therefore,it is conducive to providing theoretical guidance and decision basis for function management of Jiuduansha wetland,which is considered to be carbon sink.This study combined the field survey and laboratory analysis.We sampled in October 2015 and January,April,July 2016,determined carbon storage from different plant species and sediments and analyzed soil carbon components.In addition,we carried out a traditional decomposition bag study to compare the decomposition rate differences of the native plants and invasive S.alterniflora.The conclusion indicated that the organic carbon pool of Jiuduansha wetland was significantly improved with the invasion of S.alterniflora,which was beneficial to the carbon sequestration of Jiuduansha wetland.The results are as follows:(1)The biomass and carbon storage of S.alterniflora was higher than S.mariqueter.The biomass of S.alterniflora increased first and then decreased with invasion time,and the overall trend was: middle stage of invasion >late stage of invasion>early stage of invasion.However,there was no significant change for carbon storage with invasion time.(2)Soil organic carbon(SOC)content of S.alterniflora was higher than S.mariqueter.SOC and soil recalcitrant carbon(RC)had the same trend with invasion time,it showed that middle stage of invasion >late stage of invasion>early stage of invasion.Early stage of invasion had main impact on soil labile carbon,but RC of soil covered by S.alterniflora community showed an upward trend,which was higher than S.mariqueter in middle stage of invasion.(3)Soil organic carbon density(SOCD)of S.alterniflora was 50%~98% higher than S.mariqueter.SOCD of S.alterniflora increased first and then decreased with invasion time.(4)The trend of decomposition rate of litter in sediment surface was substantially: S.mariqueter> S.alterniflora > P.australis,and decomposition rate of standing litter in S.alterniflora was higher than P.australis.Standing litter of emergent macrophytes has an important contribution to litter decomposition in estuary wetland ecosystems.Decomposition was slower in standing than sediment surface phase for P.australis and S.alterniflora.During the incubation period,litter C and N concentrations showed similar patterns for the three species.Almost all litter treatments immobilized N and lost C to high extent in the first 90 days.With the invasion of S.alterniflora,the litter decomposition and nutrient release was distinguishing compared native plants,thus,changed the C storage.(5)The total litter decomposition was driven by both microorganisms and invertebrates in particular protozoa.Therefore,decomposition rate was faster in the coarse mesh size than fine mesh.(6)Litter chemical quality markedly affected litter decomposition,which was also influenced by surrounding environment,such as temperature and tidal inundation.(7)Plant biomass had an important impact on soil organic carbon content.And there was a significant positive correlation between soil salinity,available phosphorus or inorganic nitrogen and soil organic carbon in zhongsha and xiasha of Jiuduansha wetlands.