Influence Of Spartina Alterniflora Invasion On The Spatiotemporal Characteristics Of Soil Carbon,nitrogen,Phosphorus And Stoichiometry In A Coastal Wetland

Coastal wetlands play an important role in the global carbon,nitrogen,and phosphorus cycle,but due to the fragility of their ecosystems,they are easily invaded by foreign species.Spartina alterniflora,as one of the most successful invasive plants in the world,is widely distributed in coastal wetlands in China,and its impact on coastal wetland ecosystems has attracted widespread attention.In order to study the impact of Spartina alterniflora invasion on the carbon,nitrogen and phosphorus stoichiometric characteristics of coastal wetlands,this study,based on large-scale field survey and sampling,clarified the spatial distribution characteristics of the content and ecological stoichiometry of soil carbon,nitrogen and phosphorus in different wetland plant community.Then we compared and analyzed the soil total carbon（TC）,total nitrogen（TN）,total phosphorus（TP）,soil organic carbon（SOC）,nitrate nitrogen（NO₃^--N）,ammonium nitrogen（NH₄⁺-N）,available phosphorus（AP）content,ecological stoichiometric characteristics and seasonal dynamics of Spartina alterniflora community in different invasion years.Finally,we analyzed the correlation between soil physicochemical factors and soil carbon,nitrogen,phosphorus content,as well as ecological stoichiometric characteristics.The research will help enrich and improve the theoretical basis of wetland biogeochemistry process research,and provide effective guidance for the protection,restoration and scientific management of coastal wetland ecosystem.The main conclusions are as follows:（1）The spatial distribution of TC and TN in the 0～20 cm soil of the coastal wetlands in the study area was very similar.The highest values of TC and TN appeared in the central,southern,and western parts of the coastal wetlands in the study area,while the lowest values appeared near the eastern coast.The highest value of TP appeared in the southern,central,and eastern parts of the coastal wetlands in the study area,while the lowest value appeared in the western and northern parts of the study area.The highest soil C/N value appeared near the eastern coast of the coastal wetland in the study area,while the lowest value appeared in the central,southern,and northern regions.The highest values of C/P and N/P appeared in the central,northern,and southern coastal wetlands of the study area,while the lowest values appeared in the eastern coastal area.（2）The contents of TC and TN in 0～20 cm soil of different plant community in coastal wetlands in the study area were significantly different,but the contents of TP were not significantly different.The order of TC content was:Cynodon dactylon>Spartina alterniflora>Mudflat>Aeluropus sinensis>Suaeda salsa/Phragmites australis>Imperata cylindrica>Suaeda salsa.The order of TN content was:Cynodon dactylon>Spartina alterniflora>Mudflat>Imperata cylindrica>Suaeda salsa/Phragmites australis>Aeluropus sinensis>Suaeda salsa.The order of TP content was:Spartina alterniflora>Cynodon dactylon>Mudflat>Suaeda salsa>Aeluropus sinensis>Suaeda salsa/Phragmites australis>Imperata cylindrica.（3）There were significant differences in C/N,C/P and N/P of different plant community at 0～20 cm soil depths in the coastal wetlands of the study area.The order of C/N was as follows:Aeluropus sinensis>Suaeda salsa/Phragmites australis>Mudflat>Suaeda salsa>Spartina alterniflora>Imperata cylindrica>Cynodon dactylon.The order of C/P was as follows:Cynodon dactylon>Mudflat>Suaeda salsa/Phragmites australis>Imperata cylindrica>Aeluropus sinensis>Suaeda salsa>Spartina alterniflora.The order of C/P was as follows:Cynodon dactylon>Mudflat>Imperata cylindrica>Suaeda salsa/Phragmites australis>Aeluropus sinensis>Spartina alterniflora>Suaeda salsa.（4）The content of TC,TN,SOC,and NO₃^--N in the 0～100 cm soil of Spartina alterniflora community in the coastal wetland of the study area increased first and then decreased with the increase of invasion time of Spartina alterniflora.The NH₄⁺-N content first decreased and then increased with the increase of invasion time of Spartina alterniflora.TP content continued to decrease as the invasion time of Spartina alterniflora increases.The AP content increased in the early stage of Spartina alterniflora invasion,and then gradually decreased with the increase of Spartina alterniflora invasion time.（5）The vertical distribution of soil carbon,nitrogen,and phosphorus content in the Spartina alterniflora community of the coastal wetland in the study area varied in different invasion years.The content of TC,SOC,TN,and NH₄⁺-N in soil showed a nonmonotonic decreasing trend with the increase of soil depth within the depth range of 0～100 cm.The NO₃^--N content in the soil increased in the 0～40 cm soil layer and begins to decrease in the 40～100 cm soil layer.There was no significant change in soil TP and AP content within the depth range of 0～100 cm.（6）There were seasonal dynamic changes in soil carbon,nitrogen,and phosphorus content of Spartina alterniflora community in the coastal wetlands of the study area during different invasion years.The seasonal variation order of TC content in the sample plot of Spartina alterniflora was:winter>autumn>spring>summer.The seasonal variation order of SOC content in the sample plots of Spartina alterniflora invading for one year was as follows:summer>winter>autumn>spring.The seasonal variation order of TN content was:winter>autumn>spring>summer.The seasonal variation order of NO₃^--N content was:autumn>winter>spring>summer.The seasonal variation order of NH₄⁺-N content was:summer>spring>winter>autumn.There was no significant seasonal change in soil TP content of Spartina alterniflora community in different invasion years.（7）The soil C/N of Spartina alterniflora community in the coastal wetland of the study area showed a trend of first decreasing and then increasing with the increase of invasion time of Spartina alterniflora.The soil C/P and N/P showed a trend of first increasing and then decreasing with the increase of invasion time of Spartina alterniflora.In vertical distribution,soil C/N increased with increasing soil depth,while soil C/P and N/P decreased with increasing soil depth.In terms of seasonal dynamics,soil C/N showed:summer>spring>winter>autumn;The minimum value of soil C/P appeared in summer,the maximum value appeared in winter,the maximum value of soil N/P appeared in autumn or winter,and the minimum value appeared in summer.（8）The physical and chemical factors of coastal wetland soil in the study area were closely related to soil carbon,nitrogen,and phosphorus.There were varying degrees of correlation between soil moisture content,bulk density,conductivity,p H,and soil TC,TN,TP content,as well as C/N,C/P,N/P.Meanwhile,there were significant correlation between soil TC,TN,TP,NO₃^--N,NH₄⁺-N,and AP.