BVOCs emission in a semi-arid grassland under climate warming and nitrogen deposition

Biogenic volatile organic compounds (BVOCs) profoundly affect atmospheric chemistry and ecosystem functioning. BVOCs emission and their responses to global change are still unclear in grasslands, which cover one quarter of the Earth's land surface and are currently undergoing the largest changes. Over two growing seasons, we conducted a field experiment in a semi-arid grassland (Inner Mongolia, China) to examine the emission and the responses of BVOCs emissions to warming and nitrogen deposition. The natural emission rate (NER) of monoterpene (dominant BVOCs here) is 107 +/- 16 mu g m(-2) h(-1) in drought 2007, and 266 +/- 53 mu g m(-2) h(-1) in wet 2008, respectively. Warming decreased the standard emission factor (SEF) by 24% in 2007, while it increased by 43% in 2008. The exacerbated soil moisture loss caused by warming in dry season might be responsible for the decrease of SEF in 2007. A possible threshold of soil moisture (8.2% (v/v)), which controls the direction of warming effects on monoterpene emission, existed in the semiarid grassland. Nitrogen deposition decreased the coverage of Artemisia frigida and hence reduced the NER by 24% across the two growing seasons. These results suggest that the grasslands dominated by the extended Artemisia frigida are an important source for BVOCs, while the responses of their emissions to global changes are more uncertain since they depend on multifactorial in-situ conditions.