Green manures alter taxonomic and functional characteristics of soil bacterial communities

Authors: Leblanc, Nicholas

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2022
Publication Date: 2/2/2022
Citation: LeBlanc, N.R. 2022. Green manures alter taxonomic and functional characteristics of soil bacterial communities. Microbial Ecology. 85:684–697. https://doi.org/10.1007/s00248-022-01975-0.
DOI: https://doi.org/10.1007/s00248-022-01975-0

Interpretive Summary: Adding plant debris to soil as green manures before growing vegetable or fruit crops can reduce soilborne plant diseases and improve plant and soil health. Though poorly understood, these beneficial effects of green manures are thought to be mediated by the activity of microbes in soil. This study tested the effect of different types of green manures on soil microbes, the soilborne plant pathogen Verticillium dahliae, and growth of lettuce plants. Green manure soil amendments from broccoli, marigold, and sudangrass were added to soil containing the pathogen V. dahliae. Lettuce plants were also grown in soil amended with the three green manures. All three green manures reduced the amount of the plant pathogen Verticillium dahliae in soil compared to soil without any green manure. After twelve weeks, lettuce plants were larger in soil amended with marigold green manure compared to lettuce plants growing in soil without any green manure. Sequencing and analysis of DNA from soil showed the three green manures influenced the activity of soil microbes that can inhibit soilborne plant pathogens and alter soil nutrients. This study confirms prior research demonstrating green manures can reduce plant diseases in soil, while providing new knowledge on which soil microbes may mediate these and other beneficial effects of green manures on plant and soil health.

Technical Abstract: Incorporation of plant biomass into soil as green manure organic amendments can reduce soilborne diseases and improve crop and soil health in agricultural ecosystems. Soil microbial communities can mediate beneficial effects of these amendments, but their response to different types of green manures is poorly understood. This study tested the effect of green manures from broccoli, marigold, and sudangrass on taxonomic and functional characteristics of soil bacterial communities. Green manures were amended to field soil and maintained in microcosms artificially infested with the soilborne plant pathogen Verticillium dahliae. Lettuce seedlings were also transplanted into green manure amended and fallow soil and maintained under growth chamber conditions for twelve weeks. Bacterial communities in bulk and rhizosphere soil were characterized using nanopore sequencing of 16S rRNA and shotgun metagenome libraries. Under microcosm conditions, all green manures reduced the abundance of the soilborne plant pathogen V. dahliae and altered the taxonomic composition of bacterial communities. Twelve weeks following amendment, green manures had differential effects on lettuce yield as well as the taxonomic diversity and composition of soil bacterial communities. In addition, multiple green manures increased the abundance of bacterial functional traits in rhizosphere soil related to iron and polysaccharide acquisition and decreased the abundance of functional traits related to bacterial protein secretion systems. This study demonstrates green manures alter the taxonomic composition and functional traits in soil bacterial communities suggesting these changes may have positive impacts on beneficial effects of green manures on plant and soil health.