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

ABSTRACT

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 (CO2) and nitrous oxide (N2O) emissions but had no significant effect on methane (CH4). 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-2 yr-1-24 g N m-2 yr-1) contributed more significantly to wetland CO2 and N2O emissions. Compared to other wetland types, alpine peatlands have a greater impact on CO2 and N2O emissions following nitrogen input. In addition, high altitude (> 1500 m and ≤ 3500 m) could promote wetland CO2 and N2O emissions more significantly after nitrogen input, but ultra-high altitude (> 3500 m) reduced CO2 emissions. CO2 and N2O emissions were more significantly promoted when mean annual temperature (MAT) was positive, and CO2 emissions increased with increasing mean annual precipitation (MAP). Wetland CO2 emissions can be significantly promoted when soil is acidic, while N2O emissions can be significantly promoted when soil is alkaline. N2O 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.