Mediative Mechanism of Freezing/Thawing on Greenhouse Gas Emissions in an Inland Saline-Alkaline Wetland: a Metagenomic Analysis.

Inland saline-alkaline wetlands distributed in the mid-high latitude have repeatedly experienced freezing and thawing. However, the response of greenhouse gas (GHG) emission and microbially-mediated carbon and nitrogen cycle to freezing and thawing remains unclear. We monitored the GHG flux in an inland saline-alkaline wetland and found that, compared with the growth period, the average CO flux decreased from 171.99 to 76.61-80.71 mg/(m‧h), the average CH flux decreased from 10.72 to 1.96-3.94 mg/(m‧h), and the average NO flux decreased from 56.17 to - 27.14 to - 20.70 μg/(m‧h). Freezing and thawing significantly decreased the relative abundance of functional genes involved in carbon and nitrogen cycles. The aceticlastic methanogenic pathway was the main methanogenic pathway, whereas the Candidatus Methylomirabilis oxyfera was the most abundant methane oxidizer in the wetland. Ammonia-oxidizing archaea and denitrifier belonging to proteobacteria was the major microbial NO source, while bacteria within clade II nosZ was the major microbial NO sink. Freezing and thawing reduced the relative abundance of these genes, leading to a decrease in GHG flux.