Effects of increasing precipitation and nitrogen deposition on CH4 and N2O fluxes and ecosystem respiration in a degraded steppe in Inner Mongolia, China

Abstract

Most rangelands in temperate semiarid steppes have degraded due to over-grazing. However, the exchanges of greenhouse gases (GHG) between the degraded steppes have been poorly studied. In this study we investigated the fluxes of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) as ecosystem respiration during the growing season and their responses to simulated increases in water availability and nitrogen supply at a degraded steppe in Inner Mongolia, China. Temporal variation of ecosystem respiration (i.e., CO2 flux) was dominated by the interaction of soil temperature and moisture, whereas N2O emissions were mainly dependent on soil moisture. The ambient degraded steppe (i.e., not receiving additional water and nitrogen supplies) was a sink of CH4 (−1.41±0.04kg C ha−1) and a source of N2O (0.17±0.09kgN ha−1) during the growing season, respectively. Increases in water and nitrogen supplies significantly stimulated N2O emissions by 65–94% (p<0.05) and promoted ecosystem respiration by 47–70% (p<0.01), but did not significantly change CH4 uptake during the growing season in degraded plots. This result indicates that soil source of N2O and ecosystem respiration in degraded semiarid steppe may be strengthened with increasing precipitation and atmospheric nitrogen deposition. However, this conclusion should be examined at the annual scale in future studies.