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MS Biology Thesis Defense - Megan Kelly-Slatten

June 20 @ 1:00 pm - 2:00 pm MDT

Megan Kelly-Slatten

Genetic Variability of Cultivars Shape Biochemical Profiles in bioenergy Cropping Systems

Advisor: Dr. Marie-Anne de Graaff, Biological Sciences

Committee Members: Dr. Kevin Feris, Biological Sciences, Dr. Julie Jastrow, Argonne National Laboratory

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. Until recently, it was assumed that more persistent C was critical for long-term C storage. However, several studies have challenged this notion, suggesting that microbial residues formed by microbial assimilation of root exudates are better predictors of stable C formation. How labile and persistent C is assimilated in the soil may allow for predictions of soil C formation and stabilization. With this study, we set out 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. By examining the soil biochemical profiles of different species and cultivars, we can begin to understand the relationship between root-derived C inputs and soil C storage and stabilization. These analyses will provide insights into how genetic variation in plants can influence rhizosphere chemistry and possible implications for the stabilization of plant-derived C.

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 the sorped C pool. Given the extensive root systems of switchgrass and big bluestem, and their depth-dependent impacts on soil C and microbial communities, we quantified root impacts on soil biochemical profiles in 10 cm depth increments to a depth of 30 cm. Our study yielded two main results: 1) soil depth significantly impacted the soil biochemical profiles, but not every compound consistently increased or decreased in abundance with depth, 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 confirm that shallower depths of soil tend to have higher amounts of recently deposited water dissolved C, while at greater depths the C pool is dominated by older, more stable C. Additionally, cultivar variations in molecular abundance across soil biochemical profiles may explain variance in plant-derived C. Our data, along with previous studies on soil C storage in these ecosystems, suggest that both root-C input rates and chemistry of root-derived C input may drive root-derived soil C stabilization. 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. Therefore, adapting planting strategies for biofuel and agricultural industries like cultivar selection that promote soil C formation and stability may help mitigate the effects of climate change. Further research into evaluating differences among cultivar exudate composition, microbial community composition, and soil respiration would help to disentangle