(1100-30) Prairie species’ vulnerability to biological invasions: velvet bean (Mucuna pruriens) suppresses big bluestem (Andropogon gerardii) growth and development
Student Missouri Western State University, Department of Biology Saint Joseph, Missouri
Body of Abstract: As a consequence of land use change, agricultural repurposing, overgrazing, and biological invasions, the historical North American prairie ecosystem coverage has substantially declined in the past few decades. Big bluestem (Andropogon gerardii) is a warm season perennial species, a native grass dominating tallgrass prairies of Central North America. Our work focused on better understanding the vulnerability of this native prairie species to invasions and native-invasive species competition. In a controlled, greenhouse experiment, we found that big bluestem emergence, growth, and biomass decreased when co-planted with velvet bean (Mucuna pruriens), a semi-invasive species in the area. We found velvet bean planted alone to emerge over a week earlier, compared to beans co-planted with big bluestem, indicating a mutually suppressive effect of the two species in their initial developmental stage. Nevertheless, after 12 weeks, no differences were detected in the velvet bean’s development, height, and overall biomass, when planted alone, or in combination. On the other hand, big bluestem biomass decreased by 70%, while the shoot/root biomass ratio favored a higher shoot mass versus roots in the plants exposed to the competitive pressure, indicating repression of root growth in these plants 12 weeks after emergence. Leaves of big bluestem growing alone showed a nearly two-fold higher total chlorophyll (304 ± 23 µg m-2) than the competing grass (166 ± 14 µg m-2), 12 weeks after emergence, indicating that the competing grass was experiencing “stress-like” conditions. We attribute this effect to a potential belowground chemical interaction between the two competing species. The exact nature of these, potentially chemical interactions will be further investigated in the future.