Publication Date

8-1-2025

Date of Final Oral Examination (Defense)

6-12-2025

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biological Sciences

Supervisory Committee Chair

Marie-Anne de Graaff, Ph.D.

Supervisory Committee Member

Allison Simler-Williamson, Ph.D.

Supervisory Committee Member

Leonora Bittleston, Ph.D.

Abstract

Increased frequency of wildfire has become a significant problem in the sagebrush steppe, altering soil biogeochemical properties that promote the establishment of invasives at the expense of native species. To reduce annual grass invasion, restoration efforts often include seeding with non-native bunch grasses such as Agropyron cristatum (L.) Gaertn (crested wheatgrass [AGCR]) that outcompete cheatgrass; however, this strategy does not lead to the return of a native sagebrush steppe ecosystem. Restoring ecosystems to higher levels of native species diversity may reduce invasion and promote sustained success of restoration efforts since biodiversity can improve ecosystem functioning and promote resilience. In 2019 a plant diversity treatment field experiment was established in Owyhee County, Idaho 3 months following a fire. Plots were seeded with a diversity gradient of 2, 4, and 8 native species treatments, as well as AGCR monocultures and non-seeded control plots. Over 4 years I observed changes in plant community composition and soil microbial community composition. In year four, I collected field soil to evaluate how microbial inocula associated with Control, AGCR, 2 species and 8 species treatments impact sagebrush seedling growth. After 4 months, sagebrush seedlings were harvested for aboveground biomass, root biomass, specific root length (SRL), and fungal colonization analyses. My study yielded six main results: (1) Seeding with high native plant species diversity supported a more diverse community of plants and reduced invasion. (2) AGCR monocultures suppressed invasion by cheatgrass but did not support diverse native plant communities. (3) Increasing plant species diversity did not cause different, biologically significant increases in bacterial and fungal diversity. However, fungal and bacterial community composition did differ among diversity treatments. (4) There were no differences in aboveground biomass of sagebrush seedlings grown in treatment soils, but root biomass was the lowest in plants grown in 2 species plot soils. (5) Sagebrush grown in 2- and 8-species plot soils had higher proportions of thick, coarse roots in concert with higher proportions of fungal colonization. (6) Microbes associated with Control and AGCR treatments cycled nitrogen faster than microbes associated with the 2 and 8 species treatments.

DOI

https://doi.org/10.18122/td.2430.boisestate

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