Oribatida (Acari) communities in arable soils formed under waterlogged conditions: the influence of a soil moisture gradient

Oribatid mites make up a dominant group of soil mesofauna. These microarthropods are quite rarely researched in heavy clay soils, and their seasonal dynamics has never been studied thoroughly during the year in such an environment. The research was conducted in 1994–1995 at three sites along a small-scale moisture gradient, with the aim of describing the influence of different moisture conditions on this soil mesofaunal group and evaluating their seasonal dynamics regarding temperature and soil humidity fluctuations. The study area was characterized by a land depression in a field with clay soil, where waterlogged periods occurred, in the Eastern Slovak Lowland (Slovakia). The investigations were based on 24,890 oribatid adults from 72 species. The mean abundance and total species richness of Oribatida increased with increasing soil moisture towards the lower part of the land depression. The abundance and number of species reached a maximum at the bottom site (ca. 8000 ind.m−2 and 59 species) and was two-fold greater than at the summit site. The mean oribatid abundance and the mean species richness between the sites were compared, and significant differences were found on almost all sampling occasions, but the patterns of changes along the moisture gradient differed between study years. The seasonal fluctuations of oribatid abundance within the sites showed a pattern with spring and autumn maxima and a summer minimum only at moist depression bottom. Seasonal changes in the oribatid community composition were more pronounced at sites with lower soil moisture. Specific communities consisting of hygrophilous or eurytopic species and located at the bottom and slope sites of the depression clearly differed from those of the summit site, where xerotolerant species predominated. Ordination analysis confirmed the influence of temperature and precipitation on the species community composition. The bottom and slope site communities were dominated by the species combination of hygrophilous Microppia minus, Oxyoppia europaea and hygrotolerant Oppiella nova, while at the summit site these mites were replaced by more xerotolerant species: Ramusella insculpta, Oppiella obsoleta and Tectocepheus velatus.