Effects Of Spartina Alterniflora Invasion On Ecological Stoichiometry Characteristics Of Soil And Plant Carbon,Nitrogen And Phpsphorus In Tidal Flat Wetlands,Hangzhou Bay

As one of the most dominant invasive plants in the world,Spartina alterniflora is widely distributed on coastal salt marshes in China.Will the invasion of Spartina alterniflora affect the C(carbon),N(nitrogen),P(phosphorus)content and ecological stoichiometry changes of wetland soil and native vegetation communities? What are the main controlling factors that affect its variation? In response to the above scientific issues,this study selected the tidal flat wetland on the south bank of Hangzhou Bay as the study area,and collected different types of wetland(mudflat,Scirpus mariqueter,Spartina alterniflora and Phragmites australis)soil samples and plant samples.Combined variance,correlation analysis,redundancy analysis,and Monte Carlo permutation test to explore the spatial differences and seasonal variations of C,N,and P contents in soil and plants,and analyzed the effects of surface soil environmental factors on the ecological stoichiometry characteristics of soil-plant communities.Under the background of Spartina alterniflora invasion,the changes of C,N,P contents and their stoichiometric ratios in the samples were further discussed.Meanwhile,it explains the cycle and interaction of elements and the survival strategy of plants under environmental change.It provides scientific basis and theoretical support for effective control of invasion plants and protection of coastal wetlands.The preliminary conclusions are as follows:(1)The invasion of Spartina alterniflora changed the physical and chemical properties of the soil,especially in reducing soil p H and improving soil conductivity.On the contrary,the particle size,bulk density,and moisture of soil are extremely stability so that these properties are minimally affected by the invasion of Spartina alterniflora.The impact of Spartina alterniflora invasion on the content and storage of soil C,N,P was simultaneously.The results manifested as a significant increase in soil TN(total nitrogen)content and N storage,while the effect on the increase of TOC(total organic carbon)content and C storage was a significant increase with the increase of invasive years of Spartina alterniflora,and it was almost no correlation with TP(total phosphorus)content and P storage.The invasion of Spartina alterniflora also significantly affects the stoichiometric ratio of soil C,N,and P.The main manifestation is that soil C:N has declined sharply,while N:P has increased obviously,and C:P has rose slightly,but the effect is not significant.(2)Compared with the native vegetation of Phragmites australis and Scirpus mariqueter,the TOC,TN content in roots and the TN content in stems of Spartina alterniflora are significantly reduced.The variations in TP content of vegetation are more complicated.In winter,the TP content of Spartina alterniflora roots is much lower than that of Phragmites australis,while the TP content of stems and leaves increased significantly.In summer,the TP content in different organs of Spartina alterniflora had slightly different compared with Phragmites australis,but the TP content of roots and stems was significantly lower than that of Scirpus mariqueter.From the stoichiometric ratio of C,N and P in various organs of plants,the C:N value of Spartina alterniflora roots and stems was much higher than that of native vegetation,but there is no obvious difference among leaves.The root C:P of Spartina alterniflora was significantly higher than that of the native species of Phragmites australis and Scirpus mariqueter as well as the difference in N:P among vegetations was relatively small.The longer the invasion time was,the higher the C:P and N:P of Spartina alterniflora increased,indicating that the utilization efficiency of P of Spartina alterniflora decreased with the increase of invasion years.The correlation between soil and plant carbon,nitrogen and phosphorus could explain the above changes.The invasion of Spartina alterniflora changed the chemical cycle of elements in the soil,which resulted in changes in plant C,N,P content and ecological stoichiometry.(3)Soil environmental factors were closely related to the content of soil C,N,P and their stoichiometry characteristics,but they had a weak influence on the content of C,N,P and the stoichiometric ratio of the vegetation communities.Soil electrical conductivity had a significant negative correlation with soil TOC,C:N and C:P,but had a significant positive correlation with TN and N:P.Soil bulk density had a significant positive correlation with soil TN content and N:P ratio,while soil moisture showed the opposite rule.The finer the soil particle size was,the more the content of C and P in the soil,while the less the content of N.From the perspective of soil internal system,the TOC and TN content are always the key factors to control the stoichiometric characteristics of C,N,and P of the soil in the research area.In the soil system,soil C:N and C:P are closely related to TOC content,while soil N:P is mainly affected by soil TN content.