Tuesday, June 19, 2007 - 1:45 PM
Ponderosa Pines (Boise Centre on the Grove)

Germination and seed water status of native and exotic grasses on biological soil crusts

Shawna Zimmerman, Boise State University, Boise, ID, Roger Rosentreter, Bureau of Land Management, Boise, ID, and Marcelo Serpe, Boise State University, Boise, ID.

Biological soil crusts are commonly found throughout arid and semiarid steppe communities of the Great Basin of North America. We have investigated the effects of moss-dominated and lichen-dominated biological soil crusts on the germination of various native and exotic grasses. A biological soil crust dominated by short mosses (Bryum spp.) significantly decreased the germination of the native grass Elymus wawawaiensis and of the exotic grasses Festuca ovina and Bromus tectorum. Similarly, final germination in a crust dominated by the lichen Diploschistes muscorum was a third of that on soil. In contrast to these results, the presence of tall mosses (Syntrichia spp.) or a mixed crust comprised of various lichens and mosses did not inhibit germination of the grasses tested. Short mosses and D. muscorum reduced germination through an effect on seed water status. The water potential of seeds on the short mosses or D. muscorum was 2 to 4 MPa lower than that of seeds on soil. In addition, the seeds that germinated on D. muscorum did not penetrate this lichen and their root tips became necrotic. Our results indicate that some biological soil crusts have a negative effect on seed water status and germination. Through these effects, biological soil crusts may reduce the spread of invasive species and contribute to the development of patchy vegetation patterns in arid lands.