Ecological impact of steeplebush (Spiraea tomentosa L.) invasion on mite communities (Acari, Mesostigmata) in wet meadow ecosystems

Invasive plants are species introduced outside their natural range and often cause ecological or economic harm. By modifying litter quality, root architecture, and soil chemistry, invasive plants can alter many soil processes, including nutrient cycling and edaphic activity. The main aim of our study was to provide the first assessment in Poland of the ecological impact of Spiraea tomentosa L. invasion on the abundance, diversity, and species richness of soil Mesotigmata (Gamasida; Gamasina and Uropodnia) mite communities in wet meadow ecosystems, thereby offering novel insights into the belowground ecological consequences of this invasive species. The research was carried out in a wet meadow complex located in the Lower Silesian Forests in south-western Poland. A total of 104 soil samples were collected from 26 experimental plots (13 invaded by Spiraea tomentosa and 13 uninvaded) in May and October 2024. In total, we identified 2,502 mesostigmatid mites belonging to 71 taxa. The three most abundant mite species across the entire study were Paragamasus vagabundus (Karg) (409 ind.), Zercon gurensis Mihelčič (228), and Trachytes aegrota (C. L. Koch) (216). Mite abundance was negatively associated with soil Fe, while litter pH and litter Pb showed positive but non-significant trends. Species richness was positively associated with soil Mn and litter Pb, and negatively associated with soil Fe and litter Cu. Mite diversity showed a significant overall effect of collection time and site type, although Tukey HSD post hoc tests did not detect significant pairwise differences among treatment combinations. Moreover, Mesostigmata diversity increased with soil Mn and K and decreased with soil Fe, Na, and soil moisture. However, diversity was lower at uninvaded sites than at invaded sites. Overall, our findings show that microhabitat alteration associated with the biological invasion of Spiraea tomentosa has a complex impact on the diversity and composition of mite communities.