Publication Date

5-2014

Date of Final Oral Examination (Defense)

3-19-2014

Type of Culminating Activity

Thesis - Boise State University Access Only

Degree Title

Master of Science in Biology

Department

Biology

Major Advisor

Marie-Anne de Graaff, Ph.D.

Abstract

Biological invasion of semi-arid regions by the non-native winter annual cheatgrass (Bromus tectorum) has caused major degradation to the Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) ecosystem. Successful restoration remains rare potentially due to major gaps in our understanding of plant-soil feedbacks. Plant-AMF interactions could play an important role in the containment of invasive species and regulating the terrestrial-atmospheric carbon (C) cycle. I aimed to investigate (1) AMF abundance in plant roots of native versus cheatgrass-invaded plant communities; (2) how different AMF communities impact the performance of sagebrush and cheatgrass; (3) how AMF community impacts sagebrush C transfer to AMF and other soil microbes; and (4) how a change in C transfer belowground affects soil organic C (SOC) cycling. To assess AMF abundance in plant roots, soils were collected from three plant community types, dominant sagebrush, dominant cheatgrass, and a mixed community. Sagebrush and cheatgrass roots from dominant and mixed communities were examined and AMF structures were quantified using the magnified intersection method. To evaluate the impact of different AMF communities on plant performance and C transfer, sagebrush and cheatgrass were grown in sterilized soil amended with sagebrush- and cheatgrass-associated AMF, and sterilized soil only. Plant performance was examined by recording above- and below-ground biomass. Sagebrush seedlings were pulse-labeled with 13C and sagebrush C transfer to AMF and other soil microbes was determined based on 13C incorporation into microbial phospholipid fatty acid (PLFA) and neutral lipid fatty acid (NLFA) biomarker. To test the hypotheses that C transfer to AMF is greater and SOC decomposition is lower when grown with sagebrush-associated AMF, sagebrush plants were labeled with 13C-CO2. PLFA and NLFA were extracted from soil samples and the 13C signatures were analyzed. To assess whether altered soil communities impact root-derived C input and cycling, soil samples were incubated following labeling, and 13C-CO2 respiration was quantified throughout the incubation. I found that cheatgrass invasion does not impact AMF abundance in sagebrush roots, but when sagebrush was grown with sagebrush-associated AMF, root biomass production was greater than when sagebrush was grown with cheatgrass-associated AMF. Further, although AMF community did not significantly impact C transfer to roots and the quantity of root C input to the soil, AMF presence significantly promoted microbial decomposition of SOC.

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