Effects of Competition and Temporal Variation on the Evolutionary Potential of Two Native Bunchgrass Species

The capacity of restored plant populations to adapt to new environmental challenges depends on within-population genetic variation. We examined how much genetic and environmentally based variation for fitness-associated traits exists within populations of two native grasses commonly used for restoration in California. We were also interested in understanding how phenotypic expression of genetic variation for these traits varies with growth environment. Thirty maternal families of Elymus glaucus (Blue wild rye) and Nassella pulchra (Purple needlegrass) were sampled from both coastal and interior populations and reciprocally transplanted into three replicated common gardens with and without interspecific competition at each site. Reproductive output of families differed both among years and with competition treatments. Phenotypic expression of genetic variation in culm production differed among populations and was very low when families were grown with interspecific competition. Without interspecific competition, the degree of genetic determination peaked in year two in both species (8.4 and 15.1% in E. glaucus and N. pulchra, respectively). Significant genetic differences in reproduction and phenotypic plasticity were found among N. pulchra subpopulations sampled less than 3 km apart, further highlighting the importance of thoroughly sampling available genetic variation in populations used for restoration. The variable and generally low expression of genetic variation indicates that rates of adaptation in restored populations of these native grasses may vary temporally and may be especially slow within competitive environments.