Abstract

Nitrogen (N) limitation leads to intense competition between plants and soil microorganisms for available N. However, it is unclear how grazing affects the acquisition of N by plants and microorganisms.We conducted short-term N-15 tracer experiments during the growing season (June, early growing season; July, mid-growing season; and September, late growing season) in an alpine grassland on the Tibetan Plateau to investigate the effects of grazing on the acquisition of NO3 (-)-N, NH4 (+)-N, and glycine-N by plants and soil microorganisms. Three dominant plant species (one graminoid, Kobresia pygmaea, and two forbs, Potentilla bifurca and Potentilla multifida) were selected for the study. As these species represented > 90% of the vegetation, the plant recovery of N-15 reflected competition at the plant community.Grazing decreased the recovery of N-15 by soil microorganisms and plants by 46 and 69%, respectively, indicating that grazing strongly reduced the uptake of N-15 by plants and microorganisms and altered the partitioning of N-15 between them. Significant interactions were found between grazing, season and the different forms of N. In the absence of grazing, plants acquired relatively more N than soil microorganisms for the three forms of N in July and September, whereas the microorganisms obtained relatively more N-15 glycine in July and all three forms of N in September under grazing conditions. Under grazing, the plant root biomass played an important role in controlling plant-microbial N acquisition.Grazing alters the partitioning of inorganic and organic N between plants and soil microorganisms by reducing microbial N-15 recovery to a lesser extent than plant N-15 recovery. This indicates that heterotrophic microorganisms play an important part in N cycling in N-limited ecosystems.

Keywords

Organic N; Inorganic N; N partitioning; Grazing; Tibetan plateau

Published in

Plant and Soil
2017, Volume: 416, number: 1-2, pages: 297-308
Publisher: SPRINGER

SLU Authors

• Kardol, Paul

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Agricultural Science


Publication identifier

DOI: https://doi.org/10.1007/s11104-017-3205-1

Permanent link to this page (URI)

https://res.slu.se/id/publ/92489