Genotypic variation in cheatgrass germination strategies in contrasting climate conditions of the Great Basin and Mojave Deserts

Invasive species are among the most pressing ecological problems on earth, with Bromus tectorum L. (cheatgrass) being among the most widespread and problematic invaders in deserts of North America. Cheatgrass has distinct genotypes that can become widespread in desert ecoregions within their introduced range. The objective of this study is to compare the germination responses of a dominant genotype in the cool, semiarid Great Basin Desert to a common genotype in the hot, hyperarid Mojave Desert to test whether their germination strategies differed based on the contrasting climate of these 2 deserts. The germination responses of both genotypes were characterized using factorial combinations of 4 temperatures (0, 10, 20, and 30 degrees C), and 3 water potentials (0, -0.9, and -1.8 MPa) meant to cover the broad range of temperatures and water availability in these 2 deserts. The germination of both genotypes was equally constrained by low water potential (-1.8 MPa) and freezing temperatures but showed trends of increased germination with greater water availability and warmer temperatures. However, the Mojave genotype showed less total germination as temperature and water availability increased than the Great Basin genotype did. This interaction was particularly pronounced at 30 degrees C, where the Mojave genotype exhibited 7.3 times less germination in response to increased water availability compared to the Great Basin genotype. High-temperature dormancy may be a strategy to protect the Mojave genotype during midsummer monsoonal rains (common in the Mojave Desert) that can result in seedling mortality when hot, dry periods return at the end of summer.