The future landscape of the American Midwest could look a lot like the past -- covered in native grasslands rather than agricultural crops. This is not a return to the past, however, but a future that could depend on grasslands for biofuels, grazing systems, carbon sequestration, and other ecosystem services. A major threat to this ecosystem is an old one -- weeds and their influence on the soil.
According to a study in the journal Invasive Plant Science and Management, when invasive plants spread, they can leave behind a "legacy" of alteration in the native soil. Even after an invading species has been controlled, its effects can inhibit the regrowth of native plant species. The causes of this process are still being investigated and may involve changes in soil food webs, soil microbial communities, and mutualistic fungi.
In the study, researchers tested soil conditions for changes in composition after three growth cycles of invasive plant species. Researchers looked for changes in colonization rates, diversity, and composition of arbuscular-mycorrhizal fungi (AMF). Three exotic plant species -- crested wheatgrass, smooth brome, and leafy spurge -- were tested in a glasshouse experiment. These plants, all characterized as strong invaders, were grown in native soil collected from North Dakota grasslands. Native species, including western wheatgrass, little bluestem, and blue gramma, were also grown, and after three growth cycles, soil composition was compared among these treatments.
The findings of this study showed that (1) invasive species changed the composition of AMF communities in seedling roots of native grassland species, and (2) invasive species were less colonized by AMF, forming fewer associations than native grassland species. These findings suggest that the ecological differences in how these native and invasive plants interact with soil may be a factor in this legacy effect. While market and policy demands might lead to a native grasslands agro-ecosystem, invasive plants species could derail its establishment. Weed management must be a component of any such ecosystem, so that it is possible to establish grasslands that are useful and profitable.
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