Pairing Bouteloua gracilis with its "home-team" soil organisms enhances plant growth regardless of environmental conditions
On the Colorado Plateau, land use changes and prolonged drought are negatively impacting native plants. Bouteloua gracilis is a native perennial grass on the Colorado Plateau that is obligate to soil organisms, such as mycorrhizal fungi. Plants and soil organisms may be locally adapted to one another suggesting that benefits from soil organisms are site specific. Some evidence exists that soil organisms from a dry environment are more efficient in mitigating plant responses to drought stress. It is unclear whether soil organisms and plants are co-adapted, or if soil organisms from novel environments facilitate plant adaptations to novel environments. In this experiment, we conducted a greenhouse study to examine whether novel soil organisms would provide equal benefits to B. gracilis populations as natal soil organisms. We also examined the lasting effects of exotic plant invasion on soil organism communities, and how these altered soil communities affect native grass growth. We used soil inocula and B. gracilis individuals from two different sites to determine the benefits received from novel versus natal soil organisms. We used live soil inoculum from an area invaded by Bromus tectorum to examine how altered soil organism communities alter plant growth.
We found that plants grown in association with soil organisms from their natal site were the tallest and grew fastest (p=0.0184). We also found that plants grown in association with B. tectorum invaded soil had the lowest establishment rates and were the shortest (p=0.0022). In addition, plant roots were more colonized by arbuscular mycorrhizal fungi when paired with their home team soil organisms. These data suggests the symbiosis that occurs between B. gracilis and its soil organisms likely co-evolved and is site specific. Land managers should then be interested in preparing soil inoculum from seed collection sites to enhance performance of restoration projects in disturbed or invaded sites. In addition, B. tectorum appears to manipulate soil organism communities in a way that inhibits establishment of B. gracilis. This could be due to a reduction of mycorrhizal densities, or due to an accumulation of parasitic organisms. This negative plant-soil feedback has major implications for land managers interested in restoring landscapes invaded by B. tectorum. Matching plant populations with their natal, un-invaded soil organism communities could be the missing link in restoration following exotic species invasion.