Impact of salinity stress on shifting microbial community and regulating N2O and CO2 dynamics in alkaline wetlands.

Increasingly severe soil salinization in alkaline wetland due to elevated water evaporation under climate warming affected biogeochemical cycling processes, further threatening ecosystem imbalance and global greenhouse gas (GHG) budget. To reveal the underlying relationship between microbial dynamics, nitrous oxide (N2O) and carbon dioxide (CO2) characteristics under salinity stress in alkaline wetland, a 40-day microcosm experiment was conducted using soil collected from Zhalong wetland in northern China. The physiochemical properties, bacterial community, N2O and CO2 emissions were observed in responses to different salinity gradients (0%, 0.1%, 0.3%, 0.6%, 1.0%). The results showed that 1.0% salinity significantly increased cumulative N2O emissions by 578.5% and decreased cumulative CO2 emissions by 58.8% (p < 0.05). Increased nutrients (TOC, NO3--N) and decreased pH induced by salinity significantly regulated N2O (p < 0.05) and CO2 emissions (p < 0.01). Salinity led to significant loss of bacterial community diversity and strongly altered key bacteria related to C and N cycling. The salinity-sensitive taxa Gaiella and higher abundances of NorB than NosZ facilitated incomplete denitrification process, contributing to N2O emissions. Moreover, restrained genes involved in multiple CO2 production such as organics decomposition (glxk), microbial respiration (coxC) and methane oxidation (pmoA, pmoB) enabled alkaline wetland a CO2 sink under salinity stress. This study can provide new insights into salinity on microbial responses and GHG budgets in alkaline wetlands under the increasingly severe salinization trend.