Abstract: To explore the underlying biotic and abiotic mechanisms of ant nesting affecting soil methane (CH₄) oxidation dynamics, we used indoor methane-oxidation incubation and static chamber-gas chromatography to examine the dynamics of CH₄ oxidation in ant nest and adjacent reference soil in Xishuangbanna tropical secondary Syzygium oblatum forest. We investigated the effects of ant-mediated changes in microbial composition and diversity as well as soil properties on spatiotemporal dynamics of CH₄ oxidation rate. The results showed that: 1) Ant nesting significantly affected soil CH₄ oxidation rate. The average CH₄ oxidation rate was 36.1% higher in ant nest (0.32±0.13 pmol CH₄·g^-1·h^-1) than in adjacent soil (0.24±0.12 pmol CH₄·g^-1·h^-1). Furthermore, soil CH₄ oxidation rates in ant nest were 1.2- and 1.7-fold of that in the reference soil in wet and dry seasons, respectively. The CH₄ oxidation rates in ant nest and reference soil decreased along soil profile. In contrast to the reference soil, the CH₄ oxidation rates in 0-5, 5-10 and 10-15 cm layers increased by 39.8%, 31.6% and 36.2%, respectively. 2) Ant nesting changed the composition and diversity of soil functional microorganism. In contrast to adjacent reference soil, relative abundances of dominant order (Rhizobiales) and genus (Methylocystis) in ant nest increased by 7.3% and 30.6%, respectively. Moreover, Ace, Chao1, and Shannon indices increased by 17.6%-29.1%. 3) Ant nes-ting changed soil physicochemical properties. Compared with the adjacent reference soil, the increases in microbial biomass carbon (MBC) and nitrogen (MBN), soil organic carbon, readily oxidizable organic carbon, particulate organic carbon, total nitrogen, hydrolyzable nitrogen, ammonium nitrogen, and nitrate nitrogen ranged from 11.6% to 77.6%, while decreases in soil bulk density and pH were between 6.8% and 21.2%. 4) Variance decomposition analysis showed that soil physicochemical factors, microbial biomass, diversity and functional bacteria accounted for 57.5%, 26.8%, 18.2% and 10.8% of the variation in soil CH₄ oxidation rate, respectively. The results of random forest model indicated that MBC and MBN were the primary influencing factors of CH₄ oxidation rate, with contribution rates of 16.1% and 18.3%, respectively. The ant nesting could regulate the CH₄ oxidation in tropical secondary forests, primarily through mediating the variations in MBC and MBN.

Key words: methane oxidation, ant nesting, methane-oxidizing bacteria, tropical forest, Xishuangbanna