Invasive plants have a multitude of impacts on
plant communities through their direct and indirect effects
on soil chemistry and ecosystem function. For example,
plants modify the soil environment through root exudates
that affect soil structure, and mobilize and/or chelate
nutrients. The long-term impact of litter and root exudates
can modify soil nutrient pools, and there is evidence that
invasive plant species may alter nutrient cycles differently
from native speciesThe effects of plants on ecosystem
biogeochemistry may be caused by differences in leaf tissue
nutrient stoichiometry or secondary metabolites, although
evidence for the importance of allelochemicals in driving
these processes is lacking. Some invasive species may gain
a competitive advantage through the release of compounds
or combinations of compounds that are unique to the
invaded community—the “novel weapons hypothesis.”
Invasive plants also can exert profound impact on plant
communities indirectly through the herbicides used to
control them. Glyphosate, the most widely used herbicide
in the world, often is used to help control invasive weeds,
and generally is considered to have minimal environmental
impacts. Most studies show little to no effect of glyphosate
and other herbicides on soil microbial communities.
However, herbicide applications can reduce or promote
rhizobium nodulation and mycorrhiza formation. Herbicide
drift can affect the growth of non-target plants, and
glyphosate and other herbicides can impact significantly
the secondary chemistry of plants at sublethal doses. In
summary, the literature indicates that invasive species can
alter the biogeochemistry of ecosystems, that secondary
metabolites released by invasive species may play important
roles in soil chemistry as well as plant-plant and plantmicrobe
interactions, and that the herbicides used to control
invasive species can impact plant chemistry and ecosystems
in ways that have yet to be fully explored.