Leaf nitrogen acquisition of Leymus chinensis varies with leaf age and land use change in a semiarid grassland

Abstract

Nitrogen (N) is a determinant nutrient for plant growth, but how patterns of leaf N acquisition vary with leaf age and land use changes remain unclear. We quantified the contributions of soil ammonium (NH4+), nitrate (NO3−), and dissolved organic N (DON) to age-specific leaf N nutrient of a dominant species, Leymus chinensis, under changing land use (i.e., grazing, mowing, and grazing exclusion) in a semiarid grassland. Along the leaf age gradient, soil NO3− and DON contributed more to leaf N in younger than older leaves, while the opposite was observed for soil NH4+. Under changing land use, the relative contribution of DON was higher than inorganic N in grazing sites, while the opposite was true for mowing sites. Moreover, relative contributions of NO3− and DON increased along the restoration chronosequences of L. chinensis communities, while the opposite pattern was observed for NH4+. Variation in the relative contributions of NH4+, NO3−, and DON with land use changes was driven by soil pH, NO3– to NH4+ ratio, DON concentration and arbuscular mycorrhizae colonization, respectively. These results demonstrate that age-specific leaf N acquisition is associated with the adaptive strategies of plants. Due to differences in the biotic and abiotic factors that drive plant N acquisition, tradeoffs in N utilization of L. chinensis occur between NH4+, NO3−, and DON under land use changes in semiarid grasslands.