Changes in the abundance and structure of a soil mite (Acari) community under long-term organic and chemical fertilizer treatments

A study was conducted in an 11-year field experiment in a winter wheat–summer maize rotation agroecosystem in the North China Plain. We aimed to evaluate the changes in soil physico-chemical parameters and the abundance, diversity and community structure of soil mites, under organic fertilizer (OF) and chemical fertilizer (CF) treatments, compared to unfertilized soil as the control (U). Soil organic matter content, available potassium (K), total nitrogen (N) and hydrolyzable N were significantly higher in the plots under the OF treatment than under the other treatments. Available phosphorus (P) content was similar in OF and CF plots and higher than in the control. After continuous 11-year application, both the organic and chemical fertilizer treatments reduced the abundance and diversity of soil mites. Both types of fertilizer significantly reduced the abundance of Oribatida such as Epilohmannia sp., Xylobates sp., Scheloribates sp., and Cultroribula sp. This result was positively related to the high level of phosphorus in the two treatments, which probably suppressed fungi, thus reducing the food resources for mycophagous mites. However, the organic fertilizer remarkably increased the abundance of r-strategic, predatory Mesostigmata, such as Ascidae, possibly due to abundant prey under the nutrient-rich conditions. However, the number of predatory mites did not increase in the chemical fertilizer treatment. While organic fertilizer application did not increase the overall abundance and diversity of soil mites, especially Oribatida, parallel studies (unpublished) show that the increase in predatory Mesostigmata reflected enhanced biological activity and functioning of the bacterial decomposition pathway especially in the food web of this treatment.