Does perennial forage diversity influence microbially-mediated weed seed mortality in the soil seedbank?

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Commodities

• Agronomic: grass (misc. perennial), hay, medics/alfalfa

Practices

• Crop Production: cropping systems
• Education and Training: extension
• Pest Management: weed ecology
• Production Systems: agroecosystems
• Soil Management: soil analysis, soil microbiology

Leveraging the soil microbial community to accelerate weed seed mortality in the soil could be a novel approach to ecologically manage weedy populations. We proposed to examine whether natural crop-microbe-weed seed interactions can increase the soil microbes that accelerate weed seed mortality. Perennial forage crops have been shown to effectively reduce annual weed populations by disrupting weed life cycles, but one major knowledge gap remains: To what extent do diverse perennial crop mixtures affect weed seed mortality in the soil through microbial activity or abiotic conditions? Our treatments (7) include monocultures and all two- and three-species combinations of a perennial legume, forb and grass: alfalfa (Medicago sativa), forage chicory (Cichorium intybus), and orchard grass (Dactylis glomerata). We examine two weeds, Powell amaranth (a pigweed; Amaranthus powellii) and velvetleaf (Abutilon theophrasti), which are problematic on Pennsylvania farms. At the start of the experiment, we buried weed seeds within mesh bags in perennial treatments with retrieval of subsamples after 1, 1.5, 2 and 2.5 years of burial. Currently, we have measured soil abiotic conditions and conducted weed seed viability testing up to year 2, with a final sampling in May 2024. We propose a thorough analysis of soil abiotic factors and weed seed endophyte and soil microbial composition through Illumina 16S and ITS amplicon sequencing. Results will be shared through multilingual PSU Extension Events, a presentation in Spanish at a regional grower convention, national and local scientific meetings, and a bilingual Amaranthus weed ID brochure.  

Objective 1: To what extent does the weed seed microbiome vary across time, and does the weed seed microbiome predict weed seed mortality?  

Hypothesis 1: We hypothesize that seed microbiomes detected in our weed seed samples will predict seed mortality, and specifically, we hypothesize that samples with higher weed seed mortality will be colonized by more saprophytic and pathogenic microbes compared to seeds with higher mortality. Based on preliminary data, we have found greater microbial diversity in lower viability seeds compared to higher viability seeds, suggesting that the weed seed samples within our burial bags lose viability as they are colonized by the more diverse soil microbial community. 

Objective 2: Is weed seed mortality and the weed seed microbiome predicted by the soil microbiota?  

Hypothesis 2: We hypothesize that samples with higher weed seed mortality are colonized by more saprophytic and pathogenic microbes than seeds with lower mortality rates. These endophytic microbes will be reflected in the soil microbiota surrounding the weed seeds. 

Application of Objectives 1 and 2:  

With increased understanding of microbial taxa and/or communities that are associated with weed seed mortality in the soil, this will open the door for future research into management practices that increase these microbes to reduce the density of the weed seedbank. In the future, farmers may be able to test for the microbial weed-suppressive-potential of their soil or implement management practices to support those microbial populations, even possibly in the form of an inoculant.  

Objective 3: Do soil abiotic factors predict weed seed mortality and the seed microbiome? 

Hypothesis 3: We hypothesize that warmer soil conditions and higher N content will be associated with higher weed seed mortality due to increased microbial activity or induction of seed fatal germination.  

Application of Objective 3:  

If warmer temperatures are associated with weed seed mortality, horticultural producers could alter soil temperature at smaller scales through the use of black plastic mulch, high tunnels, or tarps. If soil nitrogen is associated with weed seed mortality, then targeted application of manure or synthetic nitrogen fertilizer would be an option for accelerating weed seed mortality in the soil.