Letter

Nature 464, 881-884 (8 April 2010) | doi:10.1038/nature08931; Received 28 April 2009; Accepted 15 February 2010

Grazing-induced reduction of natural nitrous oxide release from continental steppe

Benjamin Wolf1, Xunhua Zheng2, Nicolas Brüggemann1, Weiwei Chen2, Michael Dannenmann1, Xingguo Han3, Mark A. Sutton4, Honghui Wu3, Zhisheng Yao2 & Klaus Butterbach-Bahl1

  1. Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, Germany
  2. State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, 100029 Beijing, China
  3. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 100093 Beijing, China
  4. Centre for Ecology and Hydrology, Bush Estate, Penicuik EH26 0QB, UK

Correspondence to: Klaus Butterbach-Bahl1 Correspondence and requests for materials should be addressed to K.B.-B. (Email: klaus.butterbach-bahl@kit.edu).

Atmospheric concentrations of the greenhouse gas nitrous oxide (N2O) have increased significantly since pre-industrial times owing to anthropogenic perturbation of the global nitrogen cycle1, 2, with animal production being one of the main contributors3. Grasslands cover about 20 per cent of the temperate land surface of the Earth and are widely used as pasture. It has been suggested that high animal stocking rates and the resulting elevated nitrogen input increase N2O emissions4, 5, 6, 7. Internationally agreed methods to upscale the effect of increased livestock numbers on N2O emissions are based directly on per capita nitrogen inputs8. However, measurements of grassland N2O fluxes are often performed over short time periods9, with low time resolution and mostly during the growing season. In consequence, our understanding of the daily and seasonal dynamics of grassland N2O fluxes remains limited. Here we report year-round N2O flux measurements with high and low temporal resolution at ten steppe grassland sites in Inner Mongolia, China. We show that short-lived pulses of N2O emission during spring thaw dominate the annual N2O budget at our study sites. The N2O emission pulses are highest in ungrazed steppe and decrease with increasing stocking rate, suggesting that grazing decreases rather than increases N2O emissions. Our results show that the stimulatory effect of higher stocking rates on nitrogen cycling4, 7 and, hence, on N2O emission is more than offset by the effects of a parallel reduction in microbial biomass, inorganic nitrogen production and wintertime water retention. By neglecting these freeze–thaw interactions, existing approaches may have systematically overestimated N2O emissions over the last century for semi-arid, cool temperate grasslands by up to 72 per cent.

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