Warming influences CO₂ emissions from China's coastal saltmarsh wetlands more than changes in precipitation

Coastal wetlands are an important carbon sink but are sensitive to climate changes. The response of CO₂ emissions to these changes differs under different hydroclimatic conditions. Here, this article used meta-analysis to synthesize data from Chinese coastal salt marshes, to analyze sensitivities for CO₂ emissions, and then to assess the relative contributions of air temperature (T_a) and precipitation (Pre). This article used the ratio between potential evaporation (E_p) and Pre to divide Chinese coastal saltmarshes into water- (E_p/Pre > 1) and energy-limited regions (E_p/Pre ≤ 1). Results show that emissions are more sensitive to both Pre and T_a in water-limited regions (E¯ = 0.60 eV, slope = 0.37) than in energy-limited regions (E¯ = 0.23 eV, slope = 0.04). Comparing the relative effects of changes in T_a (△CO₂ = 21.86 mg m^-2 h^-1) and Pre (△CO₂ = 7.19 mg m^-2 h^-1) on CO₂ emissions shows that warming contributes more to changes in CO₂ emissions. The response of emissions to changes in Pre is asymmetric and shows that warmer and drier may have antagonistic effects, while warmer and wetter may have synergistic effects. There was a 2.15 mg m^-2 h^-1 change in emissions in energy-limited regions when Pre increased by 139.69 mm, and a decrease of -0.15 mg m^-2 h^-1 in emissions when Pre decreased by 1.28 mm in water-limited regions. Climate change has the greatest impact on Phragmites australis in CO₂ emissions, especially under warmer and wetter conditions in energy-limited regions. This indicates that warming drives CO₂ emissions, while changes in Pre (resulting in wetter or dryer conditions) can mitigate or strengthen CO₂ emissions from coastal wetlands in China. This article offers a new perspective and suggests that differences in hydroclimatic conditions should be considered when discussing carbon emissions from coastal wetlands.