Acclimation of coastal wetland vegetation to salinization results in the asymmetric response of soil respiration along an experimental precipitation gradient

Intensified interannual variability in precipitation is anticipated to alter soil salinization in coastal wetlands, which may significantly impact the structure and function of ecosystems, especially soil carbon cycling. However, the response patterns and mechanisms of soil respiration to precipitation changes in coastal wetlands remain uncertain. To assess the response pattern of soil respiration to altered precipitation, a field manipulation experiment with five precipitation treatments (-60%, -40%, +0%, +40%, and +60% of ambient precipitation) was conducted from 2015 to 2019 in a coastal wetland in the Yellow River Delta, China. Over five years, the responses of soil respiration along this experimental precipitation gradient were positive asymmetric, with a greater increase in soil respiration under wet treatments (by 24.3% and 27.7% under the +40% and +60% treatments, respectively) than reduction under dry treatments (by 10.3% and 4.0% under the -60% and -40% treatments, respectively). The observed positive asymmetric responses of soil respiration were associated with the decreased response of belowground biomass and leaf area index to high soil electric conductivity under decreased precipitation. Our study demonstrated that the acclimation of vegetation to salinization was a major determining factor in the asymmetric response of soil respiration along an experimental precipitation gradient in coastal wetlands. Our findings emphasize that soil salinity will play an essential role in regulating soil carbon cycles in coastal wetlands. The positive asymmetric response of soil respiration to altered precipitation indicates that the intensification of precipitation variability in the future may negatively affect the stability of the soil carbon stock.