Gradients of labile carbon inputs into the soil surrounding wood ant nests in a temperate forest

Wood ants are common in temperate forests, and while building their nests and foraging for food, they transfer large amounts of organic matter and nutrients. Here, we tested the hypothesis that wood ants generate natural gradients of labile carbon (C) inputs into the soil surrounding their nests. We selected five medium-sized wood ant (Formica aquilonia) nests in a coniferous temperate forest and established sampling points at distances of 4, 30 and 70 m from each nest. Throughfall (honeydew + aboveground vegetation leachates) and litterfall were collected regularly during a vegetative season and were analysed for labile organic C content. In addition, soil from the organic horizon (Oe + Oa), surface mineral horizon (A) and subsoil mineral horizon (B) was collected and analysed for organic matter and nutrient contents. The labile C input in throughfall increased with distance from the nest (it was 1.5-fold greater at 70 m than at 4 m). C input changed during the vegetative season and was highest in June. Litterfall was not affected by the distance from the nest. Organic matter and nutrient contents were unaffected by distance from the nest in surface soil horizons but were significantly higher near the nest (4 m) than 70 m from the nest in the subsoil mineral horizon, suggesting that surface soils are less affected by the labile C inputs than subsoils. Finally, we suggest that the gradients in labile C input surrounding wood ant nests can be used to study the effects of labile C input changes on soil properties.