Pesticide effects on nitrogen cycle related microbial functions and community composition

The extensive application of pesticides in agriculture raises concerns about their potential negative impact on soil microorganisms, being the key drivers of nutrient cycling. Most studies have investigated the effect of a single pesticide on a nutrient cycling in single soil type. We, for the first time, investigated the effect of 20 commercial pesticides with different mode of actions, applied at their recommended dose and five times their recommended dose, on nitrogen (N) microbial cycling in three different agricultural soils from southern Australian. Functional effects were determined by measuring soil enzymatic activities of beta-1,4-N-acetyliglucosaminidase (NAG) and L-leucine aminopeptidase (LAP), potential nitrification (PN), and the abundance of functional genes involved in N cycling (amoA and nifH). Effects on nitrifiers diversity were determined with amplicon sequencing. Overall, the pesticides effect on N microbial cycling was dose-independent and soil specific. The fungicides flutriafol and azoxystrobin, the herbicide chlorsulfuron and the insecticide fipronil induced a significant reduction in PN and beta-1,4-N- acetylglucosaminidase activity (P < 0.05) (NAG) in the alkaline loam soil with low organic carbon content i.e. a soil with properties which typically favors pesticide bioavailability and therefore potential toxicity. For the nitrifier community, the greatest pesticide effects were on the most dominant Nitrososphaeraceae (ammonia-oxidizing archaea; AOA) whose abundance increased significantly compared to the less dominant AOA and other nitrifiers. The inhibiting effects were more evident in the soil samples treated with fungicides. By testing multiple pesticides in a single study, our findings provide crucial information that can be used for pesticide hazard assessment. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the effects of 20 commercial pesticides on nitrogen microbial cycling in three different agricultural soils in southern Australia, showing that the effects of pesticides on N microbial cycling are dose-independent and soil-specific. Some pesticides, such as fungicides and herbicides, significantly reduced PN and NAG activities in alkaline loam soil with low organic carbon content. The most prominent effects were observed on the dominant ammonia-oxidizing archaea in the nitrifier community, particularly in soil samples treated with fungicides.