Browsing by Author "Johnson, Stephen P."

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Cropping systems modify soil biota effects on wheat (Triticum aestivum) growth and competitive ability
(2017-02) Johnson, Stephen P.; Miller, Zachariah J.; Lehnhoff, Erik A.; Miller, Perry R.; Menalled, Fabian D.
Plants alter soil biota which subsequently modifies plant growth, plant-plant interactions and plant community dynamics. While much research has been conducted on the magnitude and importance of soil biota effects (SBEs) in natural systems, little is known in agro-ecosystems. We investigated whether agricultural management systems could affect SBEs impacts on crop growth and crop-weed competition. Utilising soil collected from eight paired farms, we evaluated the extent to which SBEs differed between conventional and organic farming systems. Soils were conditioned by growing two common annual weeds: Amaranthus retroflexus (redroot pigweed) or Avena fatua (wild oat). Soil biota effects were measured in wheat (Triticum aestivum) growth and crop-weed competition, with SBEs calculated as the natural log of plant biomass in pots inoculated with living soil divided by the plant biomass in pots inoculated with sterilised soil. SBEs were generally more positive when soil inoculum was collected from organic farms compared with conventional farms, suggesting that cropping systems modify the relative abundance of mutualistic and pathogenic organisms responsible for the observed SBEs. Also, as feedbacks became more positive, crop-weed competition decreased and facilitation increased. In annual cropping systems, SBEs can alter plant growth and crop-weed competition. By identifying the management practices that promote positive SBEs, producers can minimise the impacts of crop-weed competition and decrease their reliance on off-farm chemical and mechanical inputs to control weeds, enhancing agroecosystem sustainability.
Impact of Cropping Systems, Soil Inoculum, and Plant Species Identity on Soil Bacterial Community Structure
(2017-02) Ishaq, Suzanne L.; Johnson, Stephen P.; Miller, Zachariah J.; Lehnhoff, Erik A.; Olivo, Sarah K.; Yeoman, Carl J.; Menalled, Fabian D.
Farming practices affect the soil microbial community, which in turn impacts crop growth and crop-weed interactions. This study assessed the modification of soil bacterial community structure by organic or conventional cropping systems, weed species identity [Amaranthus retroflexus L. (redroot pigweed) or Avena fatua L. (wild oat)], and living or sterilized inoculum. Soil from eight paired USDA-certified organic and conventional farms in north-central Montana was used as living or autoclave-sterilized inoculant into steam-pasteurized potting soil, planted with Am. retroflexus or Av. fatua and grown for two consecutive 8-week periods to condition soil nutrients and biota. Subsequently, the V3-V4 regions of the microbial 16S rRNA gene were sequenced by Illumina MiSeq. Treatments clustered significantly, with living or sterilized inoculum being the strongest delineating factor, followed by organic or conventional cropping system, then individual farm. Living inoculum-treated soil had greater species richness and was more diverse than sterile inoculum-treated soil (observed OTUs, Chao, inverse Simpson, Shannon, P<0.001) and had more discriminant taxa delineating groups (linear discriminant analysis). Living inoculum soil contained more Chloroflexi and Acidobacteria, while the sterile inoculum soil had more Bacteroidetes, Firmicutes, Gemmatimonadetes, and Verrucomicrobia. Organically farmed inoculum-treated soil had greater species richness, more diversity (observed OTUs, Chao, Shannon, P<0.05), and more discriminant taxa than conventionally farmed inoculum-treated soil. Cyanobacteria were higher in pots growing Am. retroflexus, regardless of inoculum type, for three of the four organic farms. Results highlight the potential of cropping systems and species identity to modify soil bacterial communities, subsequently modifying plant growth and crop-weed competition.