Most of the carbon contained in soil is in the form of organic matter. The composition of this matter is determined by plants, microbes, and soil. However, scientists do not fully understand how variation in plant inputs, the structure of microbial communities, and the physical and chemical attributes of soil interact to influence the chemical makeup of organic matter in soil. Researchers addressed this knowledge gap by coupling microbial characteristics with detailed soil chemistry from two long-term bioenergy research experiments. They found that soil in switchgrass fields had more water-soluble carbon compounds than soil in corn fields. However, the texture of the soil was more important than the crop type on the makeup of the soils’ microbial community and the chemistry of the soils’ organic matter.
Plants take carbon from the air, build cells, then release some of the carbon into the soil through roots and root exudates. Some researchers have suggested that growing biofuel crops in marginal soils, which generally have low carbon content, might be a way to remove carbon from the atmosphere and store it below the ground. One challenge is finding plants that can grow in these poor-quality soils. Perennial grasses, such as switchgrass, might survive in these conditions. However, this new research challenges the notion that switchgrass increases the accumulation of carbon in the surface soils of marginal lands.
Scientists must understand the controls on how soil organic matter accrues to identify land management strategies that improve soil health and increase carbon storage. This includes strategies for potential biofuel crops. While researchers know that more than 50 percent of soil organic matter is of microbial origin, we do not fully understand the relationships between plants, soil microorganisms, and soil organic matter chemistry.
In this study, researchers characterized the influence of crop and site on fungal and bacterial community structure, potential enzyme activity, soil carbon chemistry, and total soil carbon and nitrogen concentrations at two long-term biofuel field experiments. The two sites had both corn and switchgrass crops. One site had predominantly sandy loam soil, the other had predominately silty loam soil. The research found that the cropping system was less influential on soil microbial community structure and organic matter chemistry than soil type. Soil type was especially influential on fungal community structure and the chemical composition of relatively persistent carbon. After eight years of no-till management, silty loam soil still contained twice the total carbon and nitrogen as sandy loam soil, with no significant response to biofuel cropping system inputs. The researchers conclude this is likely due to enhanced microbial activity in surface soils of the perennial cropping system. Together, these results demonstrate that initial site selection is critical to plant–microbe interactions and substantially affects the potential for long-term carbon retention in surface soils under biofuel production.
This research was supported by an Early Career Research Program award to Kirsten S. Hofmockel and by the Great Lakes Bioenergy Research Center. Both are funded by the Department of Energy (DOE) Office of Science, Biological and Environmental Research, Genomic Science program. A portion of this work was performed in the William R. Wiley Environmental Molecular Sciences Laboratory and located at Pacific Northwest National Laboratory. Support for this research was also provided by the National Science Foundation Long-Term Ecological Research Program at the Kellogg Biological Station, and by Michigan State University AgBioResearch.