Soil organic matter is comprised of many different types of carbon. Different groups of microbes have adapted to decompose these varying carbon types. This research is developing on a study with the long-term goal of understanding how organic matter persists in soils. One of the main mechanisms for this persistence appears to be the association of organic matter with small, high-surface area iron minerals. This project’s broad outline involves making co-precipitates of iron and organic matter that likely reflect these persistent forms of organic matter in soils, and then measuring the microbial availability of that organic matter. In order to accomplish this, this specific study will conduct the key step of isolating microbes that can decompose different types of organic matter. The ability of these microbial isolates to decompose carbon in the iron-organic coprecicpitates will be tested. The study will measure the decomposition through the production of CO2(g), as that is the end-product of microbial decomposition of the organic matter. The study will determine the growth rates and general behavior of the microbial communities that were isolated from the soil using different carbon sources and also quantify the microbial communities using 16s DNA sequencing. The procedure is to first, isolate a microbial culture from an active, carbon-rich rooting zone by placing them in solutions of selective media with 1mM – 10mM of glucose, sucrose, lactate, and humic acid. Then investigate the CO<sub>2</sub> production over time with varying combinations and initial conditions. After this step, test the rate of decomposition of the iron-organic co-precipitates by these different isolated communities and also use 16s DNA sequencing to identify the microbial community members. Overall, this work will help identify which microbial communities are best suited to decompose the most persistent and resistant organic matter in soils.

Isolation of microbial cultures from different carbon sources to assess organic matter stability in soil

2019 Fall National Meeting

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