Cheatgrass (Bromus tectorum) invasion and consequent increases in fire frequency and ecosystem deterioration in sagebrush (Artemisia spp.) habitat make it difficult for native grass and shrub species to re-establish. One explanation for the poor seedling establishment is that in the long-term absence of suitable host plants, the abundance of beneficial rhizosphere microbes declines strongly. These microbes include mycorrhizal fungi, but also many beneficial bacterial species. This project will assess whether reintroduction of these microbes in cheatgrass-invaded areas improves native seedling establishment.

Specific objectives are to: 

1. analyze whether invasion of cheatgrass into pristine sagebrush ecosystems changes the rhizosphere microbial community composition and function of sagebrush (A. tridentata) and squirreltail (Elymus elymoides) consistently across broad geographical distances.
2.  determine whether inoculation with soil from pristine sagebrush habitat restores the rhizosphere community composition and function of sagebrush and squirreltail seedlings in cheatgrass-invaded areas and improves their establishment, growth, and survival.

In horticulture and forestry, it has become a widespread practice to aid establishment, growth, and survival by inoculating plants and soil with rhizosphere microorganisms. This approach also has been advocated for restoration of degraded natural ecosystems. The efficacy of these additions, however, is rarely evaluated, and it is mostly unknown whether these inoculations result in long-term stable changes in rhizosphere community composition and function.

The rhizosphere is the interface between plant roots and the soil environment, where a specialized microbial community accelerates nutrient cycling and availability, protects plants from pathogens, and improves access to other limiting resources. In return, these organisms are provided with plant-derived energy-rich substrates. The study of the rhizosphere community composition and function has great potential for improving agriculture, forestry, and ecosystem restoration.

This project will use Next Generation DNA sequencing techniques to characterize the rhizosphere community composition in pristine and cheatgrass-invaded sagebrush habitat and in response to inoculation treatments in greenhouse and field experiments. Researchers will characterize microbial community function using a new stable isotope technique and soil and root observations. Seedling growth and survival will be evaluated in response to the inoculation treatments.

Results from this study will advance scientific understanding of temporal and geographical variation in rhizosphere community composition and function in natural and disturbed ecosystems, and it will contribute to restoration ecology by testing the efficacy of rhizosphere manipulations as a tool in sagebrush restoration. Improved seedling establishment and growth will suppress cheatgrass growth, litter accumulation, and fire frequency and intensity. The benefits for the Department of Defense will include improved effectiveness of measures against cheatgrass invasion, an important aspect of natural resource management on military installations in the Great Basin. (Anticipated Project Completion - 2018)