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Thesis Information
Title: Interactive Effects of Fungal Community Structure and Soil Moisture on Wyoming Big Sagebrush Performance
Program: Master of Science in Biology
Advisor: Dr. Marie-Anne deGraaff, Biological Sciences
Committee Members: Dr. Allison Simler-Williamson, Biological Sciences; and Dr. Leonora Bittleston, Biological Sciences
Abstract
Large swathes of the North American sagebrush steppe have been converted to grazing and agriculture. Remaining fragmented areas are threatened by invasive annual grasses and associated increased fire frequency, with sagebrush restoration efforts largely unsuccessful. Poor outcomes may be due, in part, to unfavorable interactions between sagebrush seed sourced from distant locations and unfamiliar soil fungi.
A greenhouse experiment was designed to evaluate effects of rhizosphere fungal community composition on sagebrush reestablishment by answering: (1) How does inoculation with ‘coevolved’ versus ‘foreign’ fungi impact sagebrush fitness? (2) How does moisture availability modify the advantage different fungal communities provide?
Wyoming big sagebrush seed was collected from the wet end of its range and grown in sterilized soil inoculated with either its coevolved wet-site fungi, or foreign fungi from a drier sagebrush-dominated site, with sterilized-inoculum controls. Seedlings received either a wet-precipitation treatment mimicking that of the seeds’ home site or a dry-precipitation treatment mimicking that of the drier foreign inoculum source site, producing eight treatments. Sagebrush biomass, root morphology, and visible fungal root colonization were assessed after 6-7 months of growth. Generalized linear models were fitted to evaluate plant response variables as functions of inoculum source site, viability, and precipitation regime.
ITS fungal DNA sequences demonstrated that in situ rhizosphere fungal communities of mature sagebrush differed markedly in fungal taxonomic composition between the sites from which inoculum was derived. Seedling rhizosphere fungal communities at harvest also differed by treatment group. Two fungal families and two genera, one a dark septate endophytic taxon, were significantly more abundant in live treatments, but neither regularized abundances of these taxa nor root colonization predicted sagebrush growth responses, suggesting that as-yet unidentified fungal taxa or consortia may be responsible for observed biomass and morphology changes.
Live inoculum from both sites enhanced sagebrush seedling biomass when the precipitation regime imitated that of the inoculum’s source site, when compared to sterilized counterparts. Live dry-site inoculum also produced longer, finer roots under dry-site precipitation. Both findings suggest adaptation of the rhizosphere fungal community to local environmental conditions and reflect that positive impacts of inoculum on sagebrush fitness are more strongly contingent on a match between the inoculum and soil moisture than on a match between the sagebrush and its coevolved fungi. Applying local-environmentally-adapted microbial inoculum, derived from an intended restoration site, could potentially assist sagebrush in optimizing water uptake and maintaining productivity under drought conditions, thereby encouraging sagebrush establishment.