Summary:

The purpose of the study was to determine the abundance and the compo-sition of the group (Oribatida) in clods of roots of selected tree species - Scots pine, Norway spruce, Silver birch, Littleleaf linden - in the container nursery Bielawy. Field studies were carried out in 15 November 2012 on the open production area. Two samples of substrate (with roots) - from the upper (A) and the lower part (B) - were taken from the each clod. Volume of each sample amounted 50 cm3. Mites were extracted from the material in high gradient Tullgren funnels during 7 days and maintained in 70 % ethanol. Abundance of mites in the layer A ranged from 18.67 to 219.67 individuals · 100 cm-3 of substrate. These arachnids were more abundant in containers with hardwood species than in those with coniferous species. Abundance of mites in the lower layer of the culture media was 40 % lower than that in the layer A. Mites belonging to the orders: Actinedida, Mesostigmata and Oribatida were found in containers of all seedling species, in both layers of substrate. The most abundant were oribatid mites, and - among them - the Acaridida i Tarsonemida were the most numerous. In examined samples there were 6 taxons of oribatid mites: 5 - in Norway spruce seedlings, and 1-2 - in seedlings of Scots pine, Silver birch and Littleleaf linden. Index of the average species number s in layers A and B were higher in case of hardwood species seedlings. The most abundant oribatid mite species was Oppiella nova - its abundance in the layer A ranged from 6.67 to 215.13, and in the layer B from 0.40 to 119.80 individuals · 100 cm-3 of substrate. Best conditions for the development of Oppiella nova population were created in clods with Littleleaf linden roots, and then - in those of Silver birch. Numerous occurrence of this oribatid mite species can indicate a good condition of ectomycorrhizas.