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

Commodities

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

Practices

• Crop Production: cropping systems, other
• 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.