Effect of different factors dominated by water level environment on wetland carbon emissions

The exacerbation of global warming has led to changes in wetland carbon emissions worldwide. Therefore, we conducted a meta-analysis of methane (CH₄) and carbon dioxide (CO₂) emissions in wetland ecosystem and explored the underlying mechanisms. Our finding indicated that (1) water level of -50 to 30 cm (the negative value represents the depth of the groundwater table, whereas the positive value represents the height of the above-ground water table) and -10 cm will result in a large CH₄ and CO₂ emissions, respectively; (2) CO₂ and CH₄ massive emissions occurred at the temperature range of 15-20 °C and > 20 °C, respectively; (3) CH₄ and CO₂ emissions were higher when the mean annual precipitation (MAP) was between 400 and 800 mm, but lower at an range of 800-1200 mm; (4) there was no significant difference in CH₄ and CO₂ emissions in marsh over time; however, CO₂ emissions in fen were relatively high; (5) there was no significant difference in CO₂ emissions between the forest, grass, and shrub groups; there was also no significant difference in CH₄ emission within the forest group; and (6) MAP has a low impact (0.577) on the CO₂ emissions of wetlands. Collectively, our findings highlight the characteristics of wetland CH₄ and CO₂ emissions under different conditions dominated by water level, enhance our understanding of the potential mechanisms that govern these effects, and provide basis for future wetland management and restoration in the future.