Resilience of methane cycle and microbial functional genes to drought and flood in an alkaline wetland: A metagenomic analysis.

Alkaline wetlands distributed in arid or semi-arid areas are hotspots of methane (CH) emissions. Periods of drought and flood, although regular, are stressful events encountered by methanogenic anaerobes in alkaline wetlands. To investigate the response of the CH cycle of alkaline wetlands to such stresses, we take Zhalong wetland as an example, then determined the CH flux and soil microbiomes in the wetland during wet, dry, and flooded periods. The in-situ CH flux in the wet period was 9.55-17.29 mg‧m‧h, but sharply degraded to 3.37-6.61 mg‧m‧h in the dry period. It resumed to 4.51-20.80 mg‧m‧h when the wetland was flooded again, which indicated that methanogenesis is quite resilient to drought. Syntrophic acetogenesis, and subsequently aceticlastic methanogenesis, were the dominant methanogenic pathways and resisted drought. Members belonging to Syntrophobacterales were the dominant syntrophic acetogens. They enter a viable but non-culturable (VBNC) state to resist drought. The dominant Methanosarcinales have the ability to repair reactive oxygen species damage during dry periods. The community of CH sink was governed by anaerobic methanotrophs, which entered a VBNC state or used repair systems to survive dry periods. This study revealed the responses of the CH cycle and microbial functional genes to drought and flood in alkaline wetlands.