The Study On The Characteristics Of Dominant Plant Community N?P Stoichiometry In Poyang Lake Wetland

C,N and P is basis of life chemistry on earth,which affected the growth and development of biology and various physiological functions.At present,the information of regional C:N:P stoichiometric spatial pattern is more common in individual level,but the study of C:N:P stoichiometric relationship about community level is relatively scarce.The study of community stoichiometric relationship characteristics not only helps to reveal the stoichiometric mechanism of community structure and stability maintenance.But also it is of great significance to predict the response of ecosystem structure and function to global change.As the largest freshwater lake in China,Poyang lake is affected by the five rivers,including the Ganjiang river,Fuhe river,Xiuhe river,Rao river and Xinjiang river and the Yangtze river.The annual water level varies greatly and same changes were showed during the year.Therefore,it presents the landscape of the flood period inundated and large lake beach in the dry season were seen.Along the water level gradient from the lakeside high beach to the center of the lake,Poyang lake wetland has developed wetland plant communities such as water plant,wet plant,floated plant and submerged plant.These communities tend to have an absolute advantage in one species or a few species,with fewer associated species and relatively simple structures.such as Phragmites australis communities?Triarrhena lutarioriparia communities?Carex cinerascens communities?Vallisneria natans?Lour.?Hara communities.In addition,Wetland plant community affected by the fluctuation of water level in Poyang lake,which has obvious annual fluctuation in biomass,productivity and species dominance.In recent years,Due to the influence of climate change and large water conservancy projects,the flood period of Poyang lake has been reduced,and the dry period has been prolonged,and the drying trend of wetlands is obvious.Long-term drought is bound to cause wetland degradation and plant community succession.This study is based on the national nature reserve of the south rocky mountain wetland in Poyang lake.During the dry period of 2016-2017,We collected the samples of eight typical plant communities?Artemisia selengensis?Cynodon dactylon?Phragmitesaustralis?Triarrhena lutarioriparia?Zizania latifolia?Carex cinerascens?Polygonum hydropiper?Phalaris arundinacea?in the wetland area,including leaves,stems of aboveground and underground roots of the dominant species and associated species.Through biomass weighted average to evaluated comprehensively the content of C,N,P and their chemical relations in the aboveground and underground parts of the community level.This study explore the adaptation mechanism of the typical subtropical lake wetland plant community to the high dynamic water environment,and provides scientific basis for further revealing the biodiversity conservation and restoration of wetland in Poyang lake.The main results are as follows:?1?The content of C,N,P and stoichiometric relationship of dominant plant community in Poyang lake were different due to different water level gradient.The average content of plant community C in lakeside high beach?Cynodon dactylon community?Artemisia selengensis community?and lakeside beach?Phragmites australis community?Triarrhena lutarioriparia community?Zizania latifolia community?Carex cinerascens community?Polygonum hydropiper community?Phalaris arundinacea community?were 401.53 mg·g^-11 and 453.36 mg·g^-1,respectively.The average content of plant community N in lakeside high beach and lakeside beach were 22.09 mg·g^-11 and 25.69 mg·g^-1,respectively.The average content of plant community P in lakeside high beach and lakeside beach were 1.95 mg·g^-11 and1.68 mg·g^-1,respectively.There was no significant difference in the content of C,N and P in the plant community of lakeside high beach?P>0.05?,But the content of C,N and P in the lakeside beach plant community showed significant difference?P<0.05??The plant community C:N,N:P,C:P value of lakeside high beach is less than the lakeside beach,But there was no significant difference between the three.?P>0.05?,The lakeside high beach plant communities on the aboveground and underground part of the whole restricted by N?N:P<14?,and the lakeside beach plant mainly restricted by N and P?14<N:P<16??2?There were significant differences in the content of C,N,P and stoichiometry in the ground part and underground part of the plant community.The ground part C,N and P content in the plant community of the lakeside high beach was greater than the underground part,and the average C content of the aboveground and underground parts were 461.29 mg·g^-11 and 282.07 mg·g^-1,respectively,the average N content of the abovegroundandundergroundpartswere25.71mg·g^-1and14.87mg·g^-1,respectively,the average P content of the aboveground and underground parts were 2.02 mg·g^-11 and 1.81 mg·g^-1,respectively.The average content of C in the aboveground part and underground part of the lakeside beach plant community were464.39 mg·g^-11 and 431.31mg·g^-1,respectively.and the average content of N?P in the aboveground part and underground part of the lakeside beach plant community were28.21 mg·g^-1?19.18 mg·g^-1?1.7 mg·g^-1?1.65 mg·g^-1,respectively.There is little difference between the aboveground part and underground part of the lakeside high beach,while the aboveground part of C:P?243.44?is much larger than the underground part?156.14?,and the underground part and the aboveground part are limited by N?N:P<14?.The aboveground part of N:P,C:P value is greater than the underground part in the lakeside high beach,and the C:N is less than the underground part,and the aboveground part is mainly limited by P?P>16?,and the underground part is mainly restricted by N?P<14?.?3?The annual dynamic change of C,N,P content and stoichiometric of plant community was showed that C content?CV=3.55%?stay relatively stable.;N and P elements have little fluctuation,and the variation Coefficient of N?14.96%?is greater than P?11.53%?.The variation of C content in plant community:CV_??=3.36%<CV_??=5.09%,The variation coefficient of N and P on the aboveground is larger than the underground part.The C content variation coefficient?2.86%?of the lakeside high beach plant community was smaller the lakeside beach?4.25%?.However,the variation coefficients of N and P were all greater than lakeside beach.The lakeside high beach of aboveground part C:N and C:P shows a greater variability,while the C:N and C:P value were no difference between lakeside high beach and lakeside beach.Artemisia selengensis community?Polygonum hydropiper community and Phalaris arundinacea community are fluctuation year by year,internal structure of the community is poorly stable.Cynodon dactylon community?Phragmitesaustralis community?Triarrhena lutarioriparia community?Carex cinerascens community and Zizania latifolia community are fluctuation less year by year,internal structure of the community is stable.