Responses of plant and soil C:N:P stoichiometry to N addition in a desert steppe of Ningxia,Northwest China

To study the effects of nitrogen( N) addition on the plant and soil C∶ N∶ P stoichiometry is of significance in understanding the responses of ecosystem biogeochemical cycling to elevated N deposition. In this paper,a field experiment was conducted in a desert steppe of Ningxia to study the effects of N addition on C and N concentrations in green leaves of Agropyron cristatum,Stipa capillata,Lespedeza potanimill,and Cynanchum komarovii,and C,N and P concentrations in soil,with the relationships between the N limitation related plant-and soil stoichiometry analyzed. The results showed that with the increasing amount of N addition,the community aboveground biomass and species individual biomass all decreased after an initial increase. The C concentration in the green leaves of the four species had no obvious variation pattern,the N concentration in the green leaves of the four species except A. cristatum had a significant increase,while the C∶ N ratio in the green leaves of L. potanimil and C. komarovii decreased significantly. The soil total N content increased significantly,while the other soil indices had no significant responses to N addition. The individual biomass of C. komarovii had positive correlations with soil N and N∶ P ratio,the N concentration in green leaves of A. cristatum and C. komarovii was positively correlated with soil N,while the C∶ N ratios in the green leaves of S. capillata and C. komarovii were negatively correlated with soil total N. Our results indicated that short-term N addition had little effects on the soil C∶ N∶ P stoichiometry but relieved the N limitation of plant growth in desert grassland to a certain extent,and thus,increased the N uptake by green leaves,promoted the biomass accumulation of plant,and improved the leaf litter decomposition quality. These species-specific responses not only reflect flexible adaptation to environment change,but also mean that long-term elevated N deposition may change the structure of desert steppe ecosystem.