Which soil properties affect soil mite (Acari, Mesostigmata) communities in stands with various shares of European ash (Fraxinus excelsior L.)?

European ash (Fraxinus excelsior L.) is an important tree species and a critical component of European forests. Its share has gradually decreased due to the global climate crisis or fungal diseases. Therefore, it may influence dependent plant communities and soil organisms. Hence, we aimed to describe soil properties among different habitats where ash may grow and assess how these habitats affect abundance, species richness, and diversity of soil mite (Mesostigmata) communities. The study was conducted in eight stands (western Poland) grouped in four habitats differing in terms of soil conditions and stand species composition. Stands represented: (1) optimal habitats for ash growth with >90 % ash in the tree layer, (2) optimal habitats without ash in the tree layer, (3) suboptimal habitats with >60 % ash and co-dominance of Quercus robur L., and (4) transformed habitats with >60 % ash and co-dominance of Pinus sylvestris L. Soil environments within the research plots (circular plot area in each stand = 400 m2) were characterized by the description of the soil profile and 17 soil parameters provided for each of 72 soil samples. Mesostigmatid mites were extracted from 72 additionally collected samples into Berlese-Tullgren funnels, then mounted on slides and classified to species or genus levels.
In total, 362 mites were classified into 39 taxa. The most numerous taxa were Paragamasus sp. (13.0 % of all mites), Oodinychus ovalis (C. L. Koch) (11.3 %), and Paragamasus runcatellus (Berlese) (8.6 %). We found that decreasing nitrate‑nitrogen was accompanied by increasing mite abundance, species richness, and diversity. Furthermore, mesostigmatid mite abundance and species richness increased with increasing soil pH. Although soil moisture, pH of forest litter, magnesium, calcium, potassium, total nitrogen, and C/N mass ratio differed between all habitats, they did not affect Mesostigmatid abundance, species richness, and diversity. Nevertheless, analysis of variance conducted for the Canonical Correspondence Analysis model showed that habitat and pH of forest litter significantly impacted the community species composition of mesostigmatid mites. Our study provides a better understanding of the habitat requirements of soil mesostigmatid mites and, therefore, leads to improving the use of mesostigmatid mite taxa as effective bioindicators of soil and environmental quality.