The contributions of underground-nesting ants to CO₂ emission from tropical forest soils vary with species

The aboveground ant nests are admitted as hot spots for CO₂ emissions which increase heterogeneity of soil carbon (C) flux in forest ecosystems. However, little is known about effects of underground-nesting ant species on C emissions in tropical forests, where the ants have high diversity and abundance. In this study, we chose three underground-nesting ant species with different feeding-behaviors (Pheidole capellini - predominantly honeydew harvester, Odontoponera transversa - predominantly predator, and Pheidologeton affinis - scavenger) to explore their impacts on soil CO₂ emission in Xishuangbanna tropical forest, China. We observed a pronounced effect of ants on CO₂ emission, and the effect varied with ant species. The mean CO₂ emissions were 2.4 times higher in P. capellini nests than in the reference soils, while those in nests of O. transversa and P. affinis were 2.0 and 1.6 folds, respectively. The contribution of total CO₂ flux from nests of three ant species comprised 0.01-0.54% of total annual CO₂ efflux from the forest floor. The CO₂ emission in ant nests and reference soils increased exponentially with soil temperature and water. Soil water was considerably increased by ant nesting, which explained nearly 93-97% of CO₂ emissions. However, soil temperature was not significantly different between nests and reference soils, and it only explained about 54-70% of CO₂ emission. Ant species differed in increase of soil microbial biomass carbon, total organic carbon, readily oxidizable organic carbon, soil bulk density and pH, which also contributed to a diverse effect on soil CO₂ emission. We suggest that the different effects of ant species on C emission may be closely associated with diversity of ant population size, feeding-behaviors and nesting modification on soil microbial biomass carbon, and physicochemical properties (i.e., temperature, moisture, pH, Bulk density, total and readily oxidizable organic carbon) in the tropical forest.