title: Legacy effects of anaerobic soil disinfestation on soil bacterial community composition and production of pathogen-suppressing volatiles.
abstract: There is increasing evidence that microbial volatiles (VOCs) play an important role in natural suppression of soil-borne diseases, but little is known on the factors that influence production of suppressing VOCs. In the current study we examined whether a stress-induced change in soil microbial community composition would affect the production by soils of VOCs suppressing the plant-pathogenic oomycete Pythium. Using pyrosequencing of 16S ribosomal gene fragments we compared the composition of bacterial communities in sandy soils that had been exposed to anaerobic disinfestation (AD), a treatment used to kill harmful soil organisms, with the composition in untreated soils. Three months after the AD treatment had been finished, there was still a clear legacy effect of the former anaerobic stress on bacterial community composition with a strong increase in relative abundance of the phylum Bacteroidetes and a significant decrease of the phyla Acidobacteria, Planctomycetes, Nitrospirae, Chloroflexi, and Chlorobi. This change in bacterial community composition coincided with loss of production of Pythium suppressing soil volatiles (VOCs) and of suppression of Pythium impacts on Hyacinth root development. One year later, the composition of the bacterial community in the AD soils was reflecting that of the untreated soils. In addition, both production of Pythium-suppressing VOCs and suppression of Pythium in Hyacinth bioassays had returned to the levels of the untreated soil. GC/MS analysis identified several VOCs, among which compounds known to be antifungal, that were produced in the untreated soils but not in the AD soils. These compounds were again produced 15 months after the AD treatment. Our data indicate that soils exposed to a drastic stress can temporarily lose pathogen suppressive characteristics and that both loss and return of these suppressive characteristics coincides with shifts in the soil bacterial community composition. Our data are supporting the suggested importance of microbial VOCs in the natural buffer of soils against diseases caused by soil-borne pathogens.
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology, NIOO-KNAW Wageningen, Netherlands.
authors.forename: Maaike
authors.initials: M
authors.lastname: van Agtmaal
authors.affiliation: Applied Plant Research, Flowerbulbs, Nursery Stock and Fruit, Wageningen University and Research Centre Lisse, Netherlands.
authors.forename: Gera J
authors.initials: GJ
authors.lastname: van Os
authors.affiliation: Department of Terrestrial Ecology, Netherlands Institute of Ecology, NIOO-KNAW Wageningen, Netherlands.
authors.forename: W H Gera
authors.initials: WH
authors.lastname: Hol
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology, NIOO-KNAW Wageningen, Netherlands.
authors.forename: Maria P J
authors.initials: MP
authors.lastname: Hundscheid
authors.affiliation: Applied Plant Research, Subdivision Arable Farming, Multifunctional Agriculture and Field Production of Vegetables, Wageningen University and Research Centre Lelystad, Netherlands.
authors.forename: Willemien T
authors.initials: WT
authors.lastname: Runia
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology, NIOO-KNAW Wageningen, Netherlands.
authors.forename: Cornelis A
authors.initials: CA
authors.lastname: Hordijk
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology, NIOO-KNAW Wageningen, Netherlands ; Department of Soil Quality, Wageningen University and Research Centre Wageningen, Netherlands.
authors.forename: Wietse
authors.initials: W
authors.lastname: de Boer
keywords: Fungistasis; General disease suppression; Oomycetes; Pythium intermedium; Soil-borne plant pathogens; volatile organic compounds (VOCs)