Publication Date

8-2019

Date of Final Oral Examination (Defense)

6-20-2019

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Supervisory Committee Chair

Marie-Anne de Graaff, Ph.D.

Supervisory Committee Member

Kevin Feris, Ph.D.

Supervisory Committee Member

Julie D. Jastrow, Ph.D.

Abstract

The largest terrestrial carbon (C) pool on Earth is the soil, surpassing both biotic and atmospheric C pools combined. The majority of C stabilized in soil is root-derived, and root derived C is the preferred food source for the soil microbial community. Recent studies have indicated that the perennial bioenergy crops Panicum Virgatum (hereafter: switchgrass) and Andropogon Gerardii (hereafter: big bluestem) accumulate significant amounts of soil C owing to their extensive root systems, and that soil C accumulation rates are driven by inter- and intra-specific variability in plant traits. While soil C accumulation in the short term (i.e. after two growing seasons) was linked to root morphology and associated root derived C input rates, this relationship did not hold up in the long term (i.e. after four growing seasons). Given the importance of soil metabolic profiles for microbial assimilation of C and subsequent C stabilization of microbial residues, this study aimed to evaluate how six cultivars of candidate bioenergy grasses (three cultivars of switchgrass and three cultivars of big bluestem) affect the soil biochemical profile across a 30 cm depth profile in the soil. To assess the soil’s biochemical profile, we performed a water-methanol-chloroform sequential extraction, which allowed us to assess the composition of the water dissolved C pool, and also the sorbed C pool. Our study yielded two main results: 1) soil depth significantly impacted the soil biochemical profiles, with recently deposited water dissolved C dominating at shallower depths and older, more stable C dominating at greater depths, and 2) soil biochemical profiles differed among plant cultivars, but not species, indicating the importance of genetic variability in driving the soil C cycle. Our data suggest that cultivar variations in molecular abundance across soil biochemical profiles may explain variance in plant-derived C. Models currently use root biomass as the sole parameter to predict soil C influx and stabilization, but our data indicate that the chemical composition of root-derived C influx, driven by genetic variability of the cultivar, may be another important predictor of how roots might affect soil C cycling. By further understanding how variables like cultivar type impact the formation of soil C, we can better adapt planting strategies for biofuel and agricultural industries to promote soil C formation, improve its persistence, and help mitigate the effects of climate change. Additional research into evaluating differences among cultivar exudate composition, microbial community composition, and soil respiration would help to disentangle the complicated process by which plant-derived C contributes to soil C formation and stabilization.

DOI

10.18122/td/1585/boisestate

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