Impact of salinity stress on shifting microbial community and regulating N 2 O and CO 2 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 (N ₂ O) and carbon dioxide (CO ₂ ) 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, N ₂ O and CO ₂ 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 N ₂ O emissions by 578.5% and decreased cumulative CO ₂ emissions by 58.8% (p < 0.05). Increased nutrients (TOC, NO ₃ ^- -N) and decreased pH induced by salinity significantly regulated N ₂ O (p < 0.05) and CO ₂ 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 N ₂ O emissions. Moreover, restrained genes involved in multiple CO ₂ production such as organics decomposition (glxk), microbial respiration (coxC) and methane oxidation (pmoA, pmoB) enabled alkaline wetland a CO ₂ 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.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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