Ant mounds alter spatial and temporal patterns of CO2, CH4 and N2O emissions from a marsh soil

Biogenic structures produced by soil ecosystem engineers mediate soil functions and ecosystem services. Ant mounds are important biogenic structures in marsh wetlands, where they can occur at high densities. However, little information is available on their roles in the C and N cycling in these ecosystems. We measured CO2, CH4 and N2O emissions from ant mounds of three different ant species (Lasius flavus, Lasius niger and Formica candida) and estimated their contribution to the total gas emissions of soils from May to September 2010 in a Calamagrostis angustifolia-Carex schmidtii marsh wetland of the Sanjiang Plain, in northeastern China. Average CO2 emissions from ant mounds ranged from 0.84 to 1.95 g CO2 m−2 h−1 and were 1.08–3.09 times higher than from the surrounding marsh soils. Soil CO2 emissions from ant mounds were significantly influenced by mound type and sampling season. On the whole, average soil CO2 emissions from L. niger mounds were lower in comparison to those from F. candida mounds and L. flavus mounds. Ant mound soils were CH4 sinks (−0.39～−0.19 mg m−2 h−1) while the control marsh soils were CH4 emission sources (0.13–0.76 mg m−2 h−1). Soil CH4 and N2O emissions did not significantly differ among the three different types of ant mounds. Compared with control marsh soils (0.034–0.045 mg m−2 h−1), N2O emissions from ant mounds (0.007–0.13 mg m−2 h−1) were influenced more by sampling season. Overall, ant mounds contributed measurable amounts to soil gas emissions from the wetland, averaging 7.02%, −4.28% and 3.35% of total soil CO2, CH4 and N2O emission, respectively. Ant mounds also increased the spatial and temporal heterogeneity of soil gas emissions in the marsh. Thus ant mounds may be important to a complete understanding of wetland ecosystem C and N cycles and balances. Research on more ant species from more ecosystems is needed to establish ant mound impacts on soil gas emissions at a global scale.