Date of Award

January 2023

Document Type


Degree Name

Master of Science (MS)



First Advisor

Brian J. Darby


The Conservation Reserve Program (CRP) is a grassland restoration program that allows landowners to remove degraded land from crop production, seed it with a perennial seed mixture, and leave it fallow for the remainder of the contract, which usually ranges from 10-15 years. While some ecosystem functions quickly improve upon CRP enrollment, soil organic carbon is slow to return to pre-agricultural levels. One explanation is that particulate organic matter left by litter takes several years to degrade even with a full bacteria community. Alternatively, it is possible that different chemical components of organic matter require different bacteria communities for full degradation, and it takes a long time for microbial communities to turnover in their species composition (and functional capabilities) from early- to mid- to late-successional states. Common agricultural practices, such as tillage and fertilizer application, are known to alter soil bacteria community composition, but the changes that occur during restoration are less well understood. We collected soil from ~ 250 CRP grasslands in the central and western U.S. that have been enrolled in CRP between zero and 40 years. We sequenced 16S rRNA to characterize the bacteria communities for each site and used principal component analysis to visualize differences between soil communities based on time in CRP. The effect of time in CRP on bacteria composition was subtle and secondary to geographic region. Moreover, there were no detectable effects of time in CRP on the relative abundances of bacteria phyla or of classes within major phyla, suggesting that organic carbon cycling and accumulation in CRP grasslands is not simply driven by bacteria composition. Future research will clarify how bacteria functional attributes and soil physicochemical factors influence limitations on carbon accumulation during grassland restoration.

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