LAUSR

Plant carbon (C), nitrogen (N), phosphorus (P) levels and their stoichiometry and N uptake strategies are important aspects influencing vegetation composition and C dynamics in boreal peatlands. However, C, N and P levels and N sources of different plants remain poorly understood, which prevents a better assessment of plant responses to projected increasing N availability in boreal ecosystems with climate warming and increasing N deposition. We investigated differences of leaf C, N and P concentrations and C and N isotopes (δ13C and δ15N) between graminoids and shrubs in 18 peatlands in northeastern China. Ericoid mycorrhizal (ERM) and ectomycorrhizal (ECM) shrubs have higher C and P while lower C/N and C/P than nonmycorrhizal (NM) graminoids. Shrubs and graminoids have similar leaf N/P, mainly exhibiting N limitation or N and P co-limitation. ECM shrubs show higher N and lower δ15N than NM graminoids despite having similar rooting depths, indicating higher N availability and more uptake of 15 N-depleted organic N of ECM shrubs. However, deep-rooted ECM shrubs show slightly higher N than shallow-rooted ERM shrubs, and their δ15N differences are insignificant. Shallow-rooted ERM shrubs have higher N and lower δ15N than deep-rooted NM graminoids. Our results imply lower N and P use efficiencies of shrubs than graminoids, and the important role of mycorrhizal association in differentiating N availabilities and sources between shrubs and graminoids. These findings are useful for understanding peatland plant responses to environmental changes.