Microbial activity and functional diversity in the mounds of three different ant species

Activity and functional diversity of the soil microflora in the mounds of Myrmica scabrinodis, Lasius niger and L. flavus were investigated. These three ant species strongly differ in foraging strategy and in the mode of mound construction. To take account of changing microbial performances during the cycle of mound building, immature mounds of L. flavus were compared to well established ones. The study was carried out with substrate sampled in the rural district of Hohenahr-Erda (Lahn-Dill Bergland, Central Hesse, Germany). Nest abundance as well as mound size and architecture were recorded for all three species. Microbial activity was quantified by determining the C mineralization rate (C-min). Functional diversity of the microflora was measured by means of the Biolog method. Additional factors were substrate moisture and pH. Substrate moisture and pH value were not different in the mounds from that in the control. High C-min values in all mound types indicate that the mounds of the three ant species investigated form a mosaic of microbial hot spots at the study site. Substrate diversify and evenness were higher in the mounds of both M. scabrinodis and L. niger than in the control soil, but lower in the two mound types of L. flavus. The results of the Biolog measurements suggest that different components of the microbial community were activated in the different mounds. The increase of C-min in L. flavus mounds seems to be based on the stimulation of a comparatively small and specialized microbial community. The high microbial activity in the mounds of L. niger and M. scabrinodis, in contrast, is accompanied by an increase in functional diversity. Investigations on the developing L. flavus mounds show that typical features characterizing the microflora in the mounds of this species need a considerable time to develop. It is concluded that ants have an important role as soil engineers and that species specific differences in the effect on the soil microflora are related to feeding strategy and nest architecture. Methodological difficulties arising from the application of the Biolog approach are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.