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A Simplified Way to Predict the Function of Microbial Communities

Microbial C and energy balances in flooded soilsThis pioneering study offers an easier approach to study how microbes work and could help scientists advance models of the cycling of elements and nutrients in frequently flooded soils.

K. Boye, A.H. Hermann, M.V. Schaefer, M.M. Tfaily, and S. Fendorf, “Discerning microbially mediated processes during redox transitions in flooded soils using carbon and energy balances.” Frontiers in Environmental Science (2018). [DOI: 10.3389/fenvs.2018.00015]

Image courtesy of EMSL

In rice paddies and other frequently flooded areas, groups of bacteria and other microbes adapt to repeated wet-dry cycles. These microbes exert major influences; they alter the availability of nutrients to help nearby plants grow and affect carbon dioxide and other emissions. In this study, we examined three different types of frequently flooded soils from rice paddies to see how microbial activity varied in response to flooding. We used three types of organic matter that are commonly found in rice paddies: dried rice straw, charred rice straw, and cattle manure. Knowing how microbial communities work in soils—before, during, and after flooding—can help us improve models and promote beneficial changes in soil microbial functions.

We combined the use of EMSL’s Fourier-transform ion cyclotron resonance mass spectrometer to analyze dissolved carbon and then observed how microbial metabolism changed by measuring carbon use (respiration), electron acceptor utilization, and heat release (by microcalorimetry). While other studies have used a similar approach to look at well-aerated, upland soil and simple carbon compounds, or single microorganisms, none have previously examined the full complexity of natural soil and carbon substrates during the transition from dry to flooded conditions. These pioneering experiments produced some surprising results. In addition to improving our understanding of how microbial metabolism changed during flooded conditions, we discovered that a focus on the energy yield from water-extractable carbon was sufficient to predict microbial respiration rates from diverse metabolic strategies. Though more in-depth studies will be important to reveal underlying functions, the insights gained from this study suggest that water-extractable C is a reasonable proxy to use when modeling these complex interactions.