The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008
26
Soil Nitrogen Enhances the Competitive Ability of Bromus Tectorum Relative to Native Grasses
Edward A. Vasquez, Roger L. Sheley, and Tony J. Svejcar. USDA-ARS, 67826-A Hwy 205, Burns, OR 97720
Invasion by Bromus tectorum and the associated high fire frequency can displace native plant communities. Previous native plant restoration projects have met with limited success. Manipulating soil resources may be one way of influencing the success of restoration efforts. We conducted two greenhouse studies at the Eastern Oregon Agricultural Research Center in Burns, OR to test the hypotheses that (1) late-seral species will produce more biomass and be more competitive than annual grasses at low soil N concentrations, and (2) annual grasses will produce more biomass and be more competitive than late-seral species at high soil N concentrations. The first study compared the competitive relationship of Psuedoroegneria spicata, Festuca idahoensis and Hesperostipa comata with that of B. tectorum while exposed to three treatment soil concentrations of inorganic N. Densities of B. tectorum and the three native bunch grasses were arranged in growth tubes to provide randomized complete blocks of four addition-series matrices. Our second study compared the absolute growth rate of the four plant species grown in isolation in a randomized complete block design for 109 days under the same soil N treatments as the interference study. Growth of an isolated individual increased with increasing soil N concentrations for both B. tectorum and the three native perennials (p < 0.05). Biomass of B. tectorum and its competitive ability increased with increasing soil N concentrations (p < 0.0001) compared to the native plant species. The absolute growth of B. tectorum in isolation also increased with increasing N levels (p < 0.05). Ecological implications of this study suggest that soil N increases the competitive ability of B. tectorum. We speculate that nutrient levels can be modified to favor desired plant communities and that further efforts in this type of research is warranted.