Meta-analysis on the effects of nitrogen deposition on soil N 2 O flux in different habitats.

We carried out a meta-analysis to explore the effects of site characteristics (climatic factors and soil properties) and nitrogen (N) factors on soil nitrous oxide (NO) flux after N addition based on 290 data from 66 field N addition experiments in China. The results showed that mean annual precipitation, mean annual temperature, ambient N deposition rate, and soil C/N of sites were positively correlated with the increases of NO flux after N addition. Soil pH was negatively correlated with the increases of NO flux after N addition. Furthermore, soils in wetland ecosystem were most sensitive to N addition, followed by forest ecosystem, and grassland showed the lowest sensitivity. Among all the site characteristics, soil pH and C/N were the most important factors driving the responses of NO flux to N addition. Soil NO flux increased the greatest after nitrate addition. The increase of NO flux was similar after the addition of urea and ammonium, while NO flux increased the least when ammonium nitrate was added. In summary, to accurately assess and predict the response of soil NO flux to N deposition, the effects of site characteristics and N fertilizer types should be comprehensively considered.