Invasions of the annual species cheatgrass (Bromus tectorum) in North American ecosystems present a threat to the population viability of native plant and animal species. In the interest of curtailing B. tectorum success, we manipulated the biogeochemistry of Canyonlands National Park soils in greenhouse and germination experiments. We compared growth parameters of B. tectorum and a native perennial, Hilaria jamesii, in greenhouse experiments utilizing 10 soil additives. Biomass of B. tectorum growing in conjuction with H. jamesii was greater than that growing in monocultures, suggesting facilitation of Bromus growth by H. jamesii. The opposite trend was true for H. jamesii, indicating that Bromus inhibits H. jamesii growth. Bromus success was lowest in Na2HPO4 (+P) treatments as measured in germination, post-germination mortality, and shoot biomass. In germination trials using 15 soil additives and 3 different soils, higher concentrations of any treatment generally reduced Bromus germination and there was a significant positive relationship between germination and pH. In Bromus-occupied soils, treatments manipulating available P had ambiguous effects on Bromus germination while those manipulating soil K and N most consistently inhibited germination. In uninvaded Hilaria soils, MgCl2 (-K) was the most effective germination inhibitor. In uninvaded Stipa hymenoides soils, added N reduced germination. Results demonstrate the susceptibility of B. tectorum to relatively high concentrations of nontoxic soil additives and provide a framework for field tests. Published in 86th Annual Meeting of the Ecological Society of America, in 2001.
