Species specific effects of ants on microbial activity and N-availability in the soil of an old-field

Microbial biomass and activity as well as N-availability were measured in the mounds of three ant species strongly differing in foraging strategy and mound architecture: Myrmica scabrinodis, Lasius niger and L. flavus. Soil microbial biomass (C-mic) was significantly increased in the mounds of all three ant species. This positive effect was due to the accumulation of organic matter (C-org) within the mounds. Microbial activity was increased in M. scabrinodis mounds only. Available N-min was accumulated in all mound types, independent of the feeding mode of the ants, with Lasius mounds having significantly higher N-min content than M. scabrinodis mounds. It is hypothesised that the differences between the mound types are due to differences in nest architecture, especially the integration of grassy vegetation. Higher microbial activity in M. scabrinodis mounds may be a consequence of supplementary energy provided by root exudates. The amount of N-min in M. scabrinodis mounds may be reduced by increased plant uptake and by immobilisation within the microbial biomass. (C) 2001 Editions scientifiques et medicales Elsevier SAS.