15N fractionation between vegetation, soil, faeces and wool is not influenced by stocking rate

Maximilian H.O.M. Wittmer, Karl Auerswald, Philipp Schönbach, Yongfei Bai, Hans Schnyder

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Understanding stable isotope fractionation in trophic networks is important for the interpretation of stable isotope composition of ecosystem components. This work explores the influence of grazing pressure on the nitrogen isotope composition (δ15N) of vegetation (standing biomass), soil, and sheep's faeces and wool in a three-years (2005-2007) experiment with different stocking rates (0.375-2.25 sheep ha-1 year-1) in semi-arid Inner Mongolia grassland. The 15N of wool (from a yearly shearing) reflects vegetation at the whole-year grazing grounds-scale while faeces reflect that of the area grazed within a few days. Stocking rate had no effect on δ15N of vegetation and soil, and sheep's faeces and wool, although nitrogen content of bulk vegetation increased with stocking rate. Furthermore, δ15N of vegetation and diet did not differ between stocking rates. Hence, 15N fractionations between vegetation and faeces (εveg-faeces), vegetation and wool (εveg-wool), faeces and soil (εfaeces-soil) and soil and vegetation (εsoil-veg) were constants, with εveg-faeces = 3.0‰ (±0.1‰, 95% confidence interval), εveg-wool = 5.3‰ (±0.1‰), εfaeces-soil = 1.1‰ (±0.4‰) and εsoil-veg = -4.1‰ (±0.3‰). This finding is useful as it means that δ15N of wool or faeces can be used to estimate the 15N of grazed vegetation, even if grazing pressure is unknown.

Original languageEnglish
Pages (from-to)25-33
Number of pages9
JournalPlant and Soil
Volume340
Issue number1
DOIs
StatePublished - Mar 2011

Keywords

  • 15-N
  • C/N ratio
  • Cycling
  • Diet
  • Enrichment
  • Plant-animal-soil system
  • Trophic shift

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