Camponotus japonicus ant mounds indirectly accelerate leaf litter decomposition by altering soil temperature and moisture

Abstract

As ecosystem engineers, soil-inhabiting ants can influence soil properties in different ways. However, limited attention has been directed toward the role of Camponotus japonicus on litter decomposition in the Loess Plateau. This study quantified the impact of C. japonicus mounds on soil evaporation, temperature and litter decomposition. The distribution and physical properties of C. japonicus mounds in four slopes (61 m × 5 m) under different vegetation types [Korshinsk peashrub (Caragana korshinskii K.), KOP; purple alfalfa (Medicago sativa L.), ALF; natural fallow, NAF; and millet, MIL] were studied. The density of ant mounds in grass and shrublands was considerably higher than that in croplands. Farming activities and intense soil erosion in the crop slope could play a negative role in mound density. On average, half-ellipsoid ant mounds were 2.48 cm in height and 755 cm2 in basal area with 0.75 g/cm3 bulk density. The size distribution of the ant mounds was as follows: 2–3 (6.9%), 1–2 (27.3%), 0.5–1 (16.9%), 0.28–0.5 (18.2%) and <0.28 mm (30.7%). Porous ant mounds that covered the leaf litter of ALF reduced soil evaporation, increased soil temperature and indirectly accelerated leaf litter decomposition. Concentrations of soil organic matter (SOC), total N, ammonium N, nitrate N, available P and available K were higher in soil under ant mounds than those in surrounding soil under KOP, ALF and NAF. High soil moisture and temperature in the leaf litter and enhanced contact area between the soil particles and the leaf litter promoted litter decomposition and contributed to the formation of a ‘fertile island’. These findings may enrich our understanding on the effects of ant activity on soil ecosystems in semiarid areas.