No interactive effects of pesticides and plant diversity on soil microbial biomass and respiration

Non-target effects of pesticides are widespread and potentially modify essential ecosystem processes. Since microorganisms are major soil decomposers driving key processes such as organic matter decomposition, nutrient cycling and, thereby, plant productivity, effects of pesticides on soil microorganisms need to be considered. In the context of the biodiversity-ecosystem functioning debate, the question arises if pesticide effects are modulated by the diversity of the plant community. We applied pesticides (dimethoate, chlorpyrifos and fosthiazate) to plots of the Jena Experiment field site differing in plant diversity, and measured basal respiration, biomass and specific respiration of soil microorganisms. Pesticide applications either increased (chlorpyrifos and fosthiazate) or decreased (dimethoate) soil microbial parameters, but the effects neither varied with plant species nor with plant functional group richness.