Nitrogen inputs promote wetland carbon dioxide and nitrous oxide emissions in China: a meta-analysis.

Nitrogen is the most limiting nutrient in wetland ecosystems. Changing in nitrogen nutrient status has a great effect on wetland carbon and nitrogen cycling. However, there is much uncertainty as to wetland greenhouse gas emissions response to nitrogen inputs in China. In this study, we synthesized 177 paired observations from 27 studies of greenhouse gases emissions related to nitrogen additions across wetland in China. The results showed nitrogen inputs significantly contributed to wetland carbon dioxide (CO) and nitrous oxide (NO) emissions but had no significant effect on methane (CH). We further analyze the relationship between greenhouse gases emissions and soil properties, climate factors under nitrogen inputs. Regression analyses introducing explanatory variables showed that high nitrogen inputs (12 g N m yr-24 g N m yr) contributed more significantly to wetland CO and NO emissions. Compared to other wetland types, alpine peatlands have a greater impact on CO and NO emissions following nitrogen input. In addition, high altitude (> 1500 m and ≤ 3500 m) could promote wetland CO and NO emissions more significantly after nitrogen input, but ultra-high altitude (> 3500 m) reduced CO emissions. CO and NO emissions were more significantly promoted when mean annual temperature (MAT) was positive, and CO emissions increased with increasing mean annual precipitation (MAP). Wetland CO emissions can be significantly promoted when soil is acidic, while NO emissions can be significantly promoted when soil is alkaline. NO emissions increased with increasing of soil total nitrogen (TN) and soil organic carbon (SOC) contents. These findings highlight the characteristics of wetland greenhouse gas emissions following nitrogen input, and improve our ability to predict greenhouse gas emissions and help meet carbon neutrality targets.