Short-term effects of copper, cadmium and cypermethrin on dehydrogenase activity and microbial functional diversity in soils after long-term mineral or organic fertilization

A long-term field experiment was employed to evaluate the short-term effects of Cu, Cd, cypermethrin (C) and their combinations (C + Cu and C + Cd) on soil dehydrogenase activity (DHA) and microbial functional diversity (average well color development, substrate utilization, Shannon index and evenness), as well as their differences in different fertilized soils. Three fertilization modes are arranged: wheat straw compost (OM), fertilizer NPK (NPK) and no fertilization (CK). The soil microbial activities were impacted greatly by long-term fertilization. The highest DHA and the lowest functional diversity (average well color development, Shannon index and substrate utilization with exception of carbohydrate) appeared in OM soil. The functional diversity was highest in NPK soil. DHA in Cu treatment and functional diversities in Cd, Cu + C and Cd + C treatments were significantly decreased to the greatest extent in NPK soil. The order of the influence of contaminants on soil microbes was NPK > CK > OM. Despite the slight effect of cypermethrin on functional diversity, when applied together with heavy metals, especially with Cd, the negative effect was more pronounced. In sum, long-term compost application has benefits to promote DHA and decrease bioavailability of contaminants in soil. At the same time, with the microbial community shifting, the microbial functional diversity reduces greatly. Our findings suggest that more attentions should be paid to the microbial community shifts in organic farming system.