Abstract: In order to explore the ecological adaptability of two relict plants,Ammopiptanthus mongolicus and Zygophyllum xanthoxylon,organ-level allocation (stems,leaves,flowers and seeds) patterns and seasonal dynamic characteristics of carbon (C),nitrogen (N) and phosphorus (P) in these two species were analyzed.The results showed that:(1) Concentrations of C,N and P varied among organs and seasons,in which C showed the minimum coefficient of variation (CV) (ranging from 1.79% to 17.45%) and P showed the maximum CV (ranging from 15.96% to 91.78%).(2) The allocation patterns of C,N and P among organs were influenced by the growth periods.During flowering period,flowers showed the highest N and P concentrations among all the organs.During seeds maturation period,the seeds contained more N and P than other organs.During postreproductive period,A. mongolicus showed higher C,N and P concentration in leaves relative to stems,while the Z. xanthoxylon showed higher C,N and P concentration in stems compared with that in leaves.(3) The C,N and P concentration of A. mongolicus was more stable than that in Z. Xanthoxylon across the year.(4) The N∶P ratio of leaves indicated that the growth of A. mongolicus and Z. xanthoxylon was primarily limited by P.In summary,the contrasting stoichiometric characteristics of these two relic species reflected their different adaptive strategies to ambient environment.