EN
The paper focuses on the role of ants as soil engineers in three drained fens. Physical, chemical and biotic soil conditions and effects of ants on soil conditions were compared between fens differing in peat origin. Multivariate statistical methods were applied (PCA, RDA). Relationship between soil moisture, indices of soil biological activity, and the amount of nutrients released were better expressed in the anthill soil than in the adjacent soil. A lower bulk density of the anthill soil, thus, a higher soil porosity, enhanced the leaching of water- extractable, mobile metallic cations and nitric ions. The composition of humus fraction was strongly dependent on soil chemical properties. In both the anthill soil and the adjacent soil, the content of humic acids was postively related with bulk density, whereas the content of humis was related with moisture. In adjacent soil, cation exchange capacity (CEC) was positively related with the content of humic acids and with bulk density. This relationship was not so clear in the anthill soil. The direction of changes in these relationship in the anthiil soil was influenced by ant societes. The number of individuals in society determined the nest structure and the associated increase in soil humidity and porosity. The consumption by ants, thus the input of matter rich in nitrogen, influenced the functional structure of microorganisms and their activity.