Soil bacterial and fungal communities respond differently to various isothiocyanates added for biofumigation.

Ping Hu,Terry J Gentry,Emily B Hollister,Frank M Hons,Anilkumar C Somenahally

doi:10.3389/fmicb.2014.00729

Abstract

The meals from many oilseed crops have potential for biofumigation due to their release of biocidal compounds such as isothiocyanates (ITCs). Various ITCs are known to inhibit numerous pathogens; however, much less is known about how the soil microbial community responds to the different types of ITCs released from oilseed meals (SMs). To simulate applying ITC-releasing SMs to soil, we amended soil with 1% flax SM (contains no biocidal chemicals) along with four types of ITCs (allyl, butyl, phenyl, and benzyl ITC) in order to determine their effects on soil fungal and bacterial communities in a replicated microcosm study. Microbial communities were analyzed based on the ITS region for fungi and 16S rRNA gene for bacteria using qPCR and tag-pyrosequencing with 454 GS FLX titanium technology. A dramatic decrease in fungal populations (~85% reduction) was observed after allyl ITC addition. Fungal community compositions also shifted following ITC amendments (e.g., Humicola increased in allyl and Mortierella in butyl ITC amendments). Bacterial populations were less impacted by ITCs, although there was a transient increase in the proportion of Firmicutes, related to bacteria know to be antagonistic to plant pathogens, following amendment with allyl ITC. Our results indicate that the type of ITC released from SMs can result in differential impacts on soil microorganisms. This information will aid selection and breeding of plants for biofumigation-based control of soil-borne pathogens while minimizing the impacts on non-target microorganisms.

Highlights

There is increasing demand for food grown organically, using alternative pest control practices such as biofumigation, due to the concerns about the toxicity of commercial pesticides
ABUNDANCE OF SOIL FUNGAL AND BACTERIAL POPULATIONS Since our experiment design aimed to simulate various ITC releasing oilseed meal application to soil in agricultural practice, all results on soil microbial community we will be discussing here should be attributed to a combined effect of ITCs and flax oilseed meal addition instead of pure ITC effects alone
Our findings are the first to detail the impacts of various ITCs, in the presence of flax SM application, on soil fungal and bacterial community composition

Summary

Introduction

There is increasing demand for food grown organically, using alternative pest control practices such as biofumigation, due to the concerns about the toxicity of commercial pesticides. Studies adding ITCs in a pure chemical form without adding decomposable plant tissue would not resemble real-world biofumigation strategies where the ITCs would be added within plant biomass (e.g., oilseed meals—the residue remaining after extraction of oil) These studies adding only pure ITCs may detect direct impact of the ITCs on target populations but would miss any indirect effects due to changes in overall soil microbial activity, abundance, and community composition that normally occur during decomposition of organic residues (Baldrian et al, 2011; Hollister et al, 2012). Changes in non-target populations could potentially impact ecosystem functions and health by altering important soil biogeochemical processes such as C cycling (Troncoso-Rojas et al, 2009)

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Results

Conclusion