Title

Germination, Initial Seedling Establishment and Water Status of Bromus Tectorum and Vulpia Microstachys on Lichen-Dominated Biological Soil Crusts of the Northern Great Basin

Publication Date

8-2006

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Major Advisor

Marcelo D. Serpe

Abstract

Biological soil crusts (BSCs) dominated by lichens are commonly found throughout arid and semiarid steppe communities of the Great Basin of North America. I conducted growth chamber experiments to investigate the effects of these crusts on seed germination and initial seedling establishment of two grasses: Bromus tectorum and Vulpia microstachys. These species share similarities in that they are both annual grasses with similar seed type. They differ, however, in that B. tectorum is non-native and highly invasive while V. microstachys is native to North America. For each ofthese species, I recorded germination time courses on bare soil and two types of biological soil crusts; one composed predominantly of the lichen Diploschistes muscorum (lichen crust) and the other comprised of an assortment of lichens and mosses (mixed crust). On the lichen crust, the final germination percentage (GP) for both grass species was about a third of that on the soil surface. In addition to differences in GP, the mean germination time (MGT) was three to four days longer on the lichen crust than on bare soil. In contrast to the lichen crust, the mixed crust did not reduce the GP or increase the MGT compared to the soil treatment. Similar results were observed in the two species studied. For the seeds that germinated, I also measured root penetration and coleoptile emergence. For both species, root penetration on the lichen crust was lower than on the bare soil or mixed crust surfaces. The combined effects of the lichen crust on germination and root penetration resulted in an overall reduction in seedling establishment of 78% for V. microstachys and 85% for B. tectorum relative to the bare soil treatment. Thus, lichen dominated biological soil crusts can inhibit germination and root penetration, but the extent of these effects depends on the composition of the crusts.

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