不同类型湿地CO_(2)︰CH_(4)比例及其影响因素:整合分析

META-ANALYSIS ON THE CO_(2)︰CH_(4)EMISSION RATIOS AND IMPACT FACTORS IN WETLANDS

湿地是温室气体二氧化碳(CO_(2))和甲烷(CH_(4))的主要来源之一,在全球碳循环中发挥着重要作用。由于CH_(4)在百年尺度上的全球增温潜势是CO_(2)的45倍,因此深入研究湿地CO_(2)︰CH_(4)的排放比例及其影响因素对准确理解和预测湿地碳循环过程及其对未来全球变化的响应具有重要意义。本文采用文献整合分析方法,对比了不同类型湿地中CO_(2)︰CH_(4)排放比例的特征及其影响因素。结果表明,藓类泥炭沼泽、滨海湿地和稻田中CO_(2)︰CH_(4)排放比例显著高于草本沼泽、河流湿地和湖泊湿地等其他类型湿地;相关性分析研究发现,湿地CO_(2)︰CH_(4)排放比例与pH和水位显著负相关,与盐度显著正相关。可见,藓类泥炭沼泽低水位和低pH抑制CH_(4)排放是导致其CO_(2)︰CH_(4)排放比例较高的重要原因,而滨海湿地高盐分抑制CH_(4)排放是其CO_(2)︰CH_(4)排放比例高的重要原因。与自然湿地相比,稻田CO_(2)︰CH_(4)排放比例高与其人为施肥和稻草还田抑制CH_(4)排放有关。此外,大气温度、土壤温度、降水量、土壤含水率等因子也对湿地CO_(2)︰CH_(4)排放比例具有重要影响,尽管它们之间的线性相关关系不显著。目前,湿地CO_(2)︰CH_(4)排放比例和影响因素仍存在很大的不确定性,未来亟待加强不同类型湿地CO_(2)︰CH_(4)排放比例及其关键影响因素研究。

Wetlands as one of the major sources of greenhouse gases carbon dioxide(CO_(2))and methane(CH_(4))to the atmosphere,play an important role in the global carbon cycle.As CH_(4)has a global warming potential more than 45 times higher than CO_(2)on a 100-year time scale,it is essential to investigate wetland CO_(2)︰CH_(4)emission ratios and their impact factors for accurately understanding and predicting wetland carbon cycle and its response to global changes.In this study,a meta-analysis was conducted to compare the CO_(2)︰CH_(4)emission ratios among various wetland types and their impact factors.We find that the CO_(2)︰CH_(4)emission ratios were significantly higher in bogs,coastal wetlands and paddy fields than in other wetlands(e.g.,marsh,riparian wetlands and lakes),and CO_(2)︰CH_(4)emission ratios were significantly and negatively correlated to pH and water table,and positively correlated to salinity.These results imply that lower water table and lower pH inhibit CH_(4)emissions may be the main reason for the higher CO_(2)︰CH_(4)ratio in bogs,while the higher salinity plays an important role in coastal wetlands.Compared to natural wetlands,fertilization and returning straw to paddy soil have a considerable contribution to the higher CO_(2)︰CH_(4)ratio by reducing CH_(4)emission in paddy fields.Meanwhile,the CO_(2)︰CH_(4)ratios are also influenced by other factors including air temperature,soil temperature,precipitation and soil water content,although they do not show any significant correlations in this study.At present,there are still large uncertainties about wetland CO_(2)︰CH_(4)emission ratios and their impact factors,therefore,future research on CO_(2)︰CH_(4)emission ratios and their main controlling factors in different wetland types needs to be strengthened urgently.