Grazing exclusion alters soil methane flux and methanotrophic and methanogenic communities in alpine meadows on the Qinghai-Tibet Plateau.

Grazing exclusion (GE) is an effective measure for restoring degraded grassland ecosystems. However, the effect of GE on methane (CH) uptake and production remains unclear in dominant bacterial taxa, main metabolic pathways, and drivers of these pathways. This study aimed to determine CH flux in alpine meadow soil using the chamber method. The composition of soil aerobic CH-oxidizing bacteria (MOB) and CH-producing archaea (MPA) as well as the relative abundance of their functional genes were analyzed in grazed and nongrazed (6 years) alpine meadows using metagenomic methods. The results revealed that CH fluxes in grazed and nongrazed plots were -34.10 and -22.82 μg‧m‧h, respectively. Overall, 23 and 10 species of Types I and II MOB were identified, respectively. Type II MOB comprised the dominant bacteria involved in CH uptake, with constituting the dominant taxa. With regard to MPA, 12 species were identified in grazed meadows and 3 in nongrazed meadows, with constituting the dominant taxa. GE decreased the diversity of MPA but increased the relative abundance of dominated species from 1.47 to 4.69%. The proportions of type I MOB, type II MOB, and MPA that were considerably affected by vegetation and soil factors were 68.42, 21.05, and 10.53%, respectively. Furthermore, the structural equation models revealed that soil factors (available phosphorus, bulk density, and moisture) significantly affected CH flux more than vegetation factors (grass species number, grass aboveground biomass, grass root biomass, and litter biomass). CH flux was mainly regulated by serine and acetate pathways. The serine pathway was driven by soil factors (0.84,  < 0.001), whereas the acetate pathway was mainly driven by vegetation (-0.39,  < 0.05) and soil factors (0.25,  < 0.05). In conclusion, our findings revealed that alpine meadow soil is a CH sink. However, GE reduces the CH sink potential by altering vegetation structure and soil properties, especially soil physical properties.