Seasonal flooding amplifies the positive asymmetric response of ecosystem carbon exchange along the precipitation gradient in saline wetlands
Description
Intensified precipitation variability profoundly affects saline wetland hydrological dynamics, potentially interfering with key carbon processes within ecosystems. However, the mechanisms underlying how precipitation changes affect ecosystems carbon processes in saline wetland remain unclear. Moreover, whether seasonal flooding influences wetland ecosystems' carbon processes response to precipitation changes is still poorly understood. Based on a six-year field precipitation experiment including five precipitation levels (-60%, -40%, +0%, +40%, and +60% of ambient precipitation) in the Yellow River Delta wetlands, we examined how seasonal flooding regulated ecosystem CO2 exchange (NEE), gross primary production (GPP) and ecosystem respiration (ER) response to precipitation changes. From 2018 to 2020, we acquired the aforementioned datasets concerning ecosystem carbon fluxes and environmental factors. Through the integration and statistical analysis of these datasets, we have summarised the following research findings. Over three years, ecosystem carbon fluxes exhibited a positive asymmetric response along the precipitation gradient, with the increment under wet treatments exceeding the reduction under dry treatments. Compared with the control, the -60% treatment significantly reduced GEP and ER by 9.7% and 9.3% respectively; whereas the +40% and +60% treatments significantly increased GEP, ER, and NEE by 18.0%, 23.5%, 15.4%, 19.4%, 22.1%, and 29.0% respectively. Moreover, the observed positive asymmetry in ecosystem carbon flux arose because, under reduced precipitation, vegetation coverage and total biomass were less affected by high soil salinity. Additionally, plants coverage responded differently to flooding under precipitation treatments: saline plants were most affected under reduced precipitation, while gramineous plants showed no significant difference.