Ecological stoichiometrical analysis on the strategies of utilization of nitrogen and phosphorus in Phragmites australis and Spartina alterniflora in Chongming Dongtan wetland

N and P contents and N:P in different organs of Phragmites australis and Spartina alterniflora and habitat soil in the typical plant community in Chongming Dongtan wetland were measured.Based on the seasonal dynamics and the strategy of N and P utilization of the two species were analyzed using the theory of ecological stoichiometry.The results showed that the contents of N and P in the two species differed significantly,and the order was P.australisS.alterniflora.The contents of N and P in different species and the different organs of the same species differed in course of plant growth.The allocation of N and P in different organs of P.australis and S.alterniflora was in the order of leafstemroot.N and P contents of the above-and below-ground parts of the two species,was in the order of MaySeptemberJuly.Accumulation of N and P in P.australiswas higher than those in S.alterniflora.The contents of N and P in the above-ground parts of the two species differed significantly.N contents in S.alterniflora habitat soil were more than those of P.australis.Only in May,soil P contents in S.alterniflora habitats were more than that in P.australis,but in July and September,soil P contents in P.australismore than those in S.alterniflora habitats.N contents in leaves of P.australis were not significantly correlated with those in its habitat soil,while P contents in leaves of P.australis were significantly positively correlated with P contents in its habitat soil.The N contents in leaves of S.alterniflora were significantly positively correlated with soil N contents in its habitat soil,while P contents in leaves of S.alterniflora were not significantly correlated with P contents in its habitat soil.The N:P ratio in leaves of and S.alterniflora had no significant correlation with N,P contents and N:P in habitat soil.At the early and last growth stage,N:P14 for P.australis,suggesting the growth of P.australis at these stages were N-limited,but at the fast growth stage,14N:P16 for P.australis,suggesting the growth of P.australis at this stage was N-and P-limited.For S.alterniflora,N:P14 in May,July and September,suggesting that the growth of S.alterniflora was N-limited.Generaly,the primary productivity of P.australis and S.alterniflora was N-limited at most cases.