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Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/15/2009 Publication Date: 7/15/2009 Citation: Blank, R.R. 2009. Intraspecific and interspecific pair-wise seedling competition between exotic annual grasses and native perennials: Plant-soil relationships. Plant and Soil. 326:331-343. Interpretive Summary: The study was conducted to examine competition and plant-soil relationships in the seedling stage among the exotic invasive annual grasses cheatgrass and medusahead and the native perennial grasses squirreltail and bluebunch wheatgrass. Soil evaluated included an arid soil (argid) presented invaded by cheatgrass and a high elevation soil (aquept). The exotic species had significantly greater above-ground biomass than the natives and grew far better in the aquept soil than the argid soil. Growth of cheatgrass, and to some degree, medusahead was suppressed when competing against themselves and enhanced, especially in the aquept soil, when competing with the natives. Overall, the data suggest that, in the seedling state, cheatgrass is a superior competitor. Moreover, squirreltail and bluebunch wheatgrass may increase the availability of mineral N and other nutrients in their rooting zone and enhance competitive pressure from cheatgrass and medusahead. Technical Abstract: Few studies have examined plant-soil relationships in competitive arenas between exotic and native plants in the western United States. A pair-wise competitive design was used to evaluate plant-soil relationships between seedings of the exotic annual grasses Bromus tectorum and Taentherium caput-medusae and the native perennial grasses Elymus elymoides and Pseudoroegneria spicata. Two soils were tested: an arid soil (argid) occupied by E. elymoides and presently invaded by B. tectorum and a high elevation, high organic matter, soil (aquept) where none of the tested species would typically occur. Plant growth proceeded for 85 days at which time above-ground biomass and tissue nutrient concentrations were quantified. Soil also was collected from the rooting zone beneath each species and analyzed for various nutrient pools. The exotic species had significantly greater above-ground biomass than the natives and grew far better in the aquept soil than the argid soil. Growth of B. tectorum, and to some degree, T. caput-medusae was suppressed in intra-specific competition and enhanced, especially in the aquept soil, when competing with the natives. Although not significant, biomass of natives strongly trended downward when competing with the exotic grasses. Overall, concentrations of tissue nutrients were minimally affected by competition, but natives tended to be more negatively affected by competition with exotics. Except for phosphorus (P), all species had significantly greater nutrient concentrations when growing in the aqept soil compared to the argid soil. In both soils, exotics had significant greater tissue concentrations of manganese (Mn), magnesium (Mg), and iron (Fe), while natives had significantly greater nitrogen (N). Species affects on soil nutrient pools occurred mostly in the aquept soil with exotic species significantly decreasing pools of available N, potentially available N, and soil-solution pools of calcium (Ca2+), potassium (K+), and magnesium (Mg2+) relative to natives. Overall, the data suggest that, in the seedling state, B. tectorum is a superior competitor. Moreover, E. elymoides and P. spicata may increase the availability of mineral N and other nutrients in their rooting zone and enhance competitive pressure from B. tectorum and T. caput-medusae. |
