Effects of ant nests on soil CH₄ emissions from Syzygium oblatum communities of a secondary tropical forest

Exploring the effects of ant nests on soil CH₄ emissions in the secondary tropical forests is of great scientific significance to understand the contribution of soil faunal activities to greenhouse gas emissions. With static chamber-gas chromatography method, we measured the dry-wet seasonal dynamics of CH₄ emissions from ant nests and control soils in the secondary forest of Syzygium oblatum communities in Xishuangbanna. We also examined the linkages of ant-mediated changes in functional microbial diversity and soil physicochemical properties with CH₄ emissions. The results showed that: 1) Ant nests significantly accelerated soil CH₄ emissions, with average CH₄ emissions in the ant nests being 2.6-fold of that in the control soils. 2) The CH₄ emissions had significant dry-wet seasonal variations, which was a carbon sink in the dry seasons (from -0.29±0.03 to -0.53±0.02 μg·m^-2·h^-1) and a carbon source in the wet seasons (from 0.098±0.02 to 0.041±0.009 μg·m^-2·h^-1). The CH₄ emissions were significantly higher in ant nests than in control soils. The CH₄ emissions from the ant nests had smaller dry-wet seasonal variation (from -0.38±0.01 to 0.12±0.02 μg·m^-2·h^-1) than those in the control soils (from -0.65±0.04 to 0.058±0.006 μg·m^-2·h^-1). 3) Ant nests significantly increased the values (6.2%-37.8%) of soil methanogen diversity (i.e., Ace and Shannon indices), temperature and humidity, carbon pools (i.e., total, easily oxidizable, and microbial carbon), and nitrogen pools (i.e., total, hydrolyzed, ammonium, and microbial biomass nitrogen), but decreased the diversity (i.e., Ace and Chao1 indices) of methane-oxidizing bacteria by 21.9%-23.8%. 4) Results of the structural equation modeling showed that CH₄ emissions were promoted by soil methanogen diversity, temperature and humidity, and C and N pools, but inhibited by soil methane-oxidizing bacterial diversity. The explained extents of soil temperature, humidity, carbon pool, nitrogen pool, methanogen diversity, and methane-oxidizing bacterial diversity for the CH₄ emission changes were 6.9%, 21.6%, 18.4%, 15.2%, 14.0%, and 10.8%, respectively. Therefore, ant nests regulated soil CH₄ emission dynamics through altering soil functional bacterial diversities, micro-habitat, and carbon and nitrogen pools in the secondary tropical forests.