Title: Effects of grazing on the δ~(15)N values of foliage and soil in a typical steppe ecosystem in Inner Mongolia,China
Abstract: Aims Stable N isotope signature(δ15N) in both plant and soil is potentially an important parameter to evaluate N cycling in grassland ecosystems. Grazing is a dominant land use in northern China grasslands and might have greatly changed N cycling. Our objective was to determine the 15N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ15N values in an ecosystem are affected by grazing. Methods We collected foliar and soil samples in a nearly 20 years fenced plot and an adjacent freely grazed plot. The foliar samples came from eight dominant species,including three perennial legumes(Caragana microphylla,Astragalus galactites and Melilotoides ruthenica) ,two grasses(Leymus chinensis and Stipa grandis) ,two forbs(Heteropappus altaicus and Potentilla acaulis) and a semi-shrub(Kochia prostrata) . We also sampled 0–10 and 10–20 cm rhizosphere soils of C. microphylla and K. prostrata. Nitrogen isotope ratios were determined with a Thermal Finnigan MAT Deltaplus XP isotope-ratio mass spectrometer(IRMS) . Important findings Although the δ15N value of leaves of different plant species varied greatly,the observed pattern of variability is consistent in both grazed and fenced plots,i.e.,semi-shrub forbs and grasses legumes. Long-term grazing reduced foliar δ15N values of forbs,semi-shrub and S. grandis significantly while changing little or even increasing that of potential biological N fixers(legumes and L. chinensis) . As the only arbuscular mycorrhizae non-infected plant species,K. prostrata is enriched in 15N(with δ15N values of 4.34‰ ± 0.35‰ and 2.04‰ ± 0.20‰ in fenced and grazed plots,respectively) compared with the depletion of other species. Mycorrhizal association may be considered to play an important role in plant nutrient transfer in those N-limited grassland ecosystems. In contrast to results of previous studies,soil δ15N values decreased significantly with grazing.
Publication Year: 2010
Publication Date: 2010-01-01
Language: en
Type: article
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