Collaborative Research: The role of phyllosilicate minerals in mediating the temperature sensitivity of soil organic matter decomposition

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Soils contain abundant organic carbon, mostly in intimate association with fine-grained phyllosilicate minerals (interchangeably called clay minerals). Mineral-associated organic carbon is believed to be stable against microbial respiration because of various protection mechanisms, which ultimately decrease the amount of greenhouse gas emission. However, current biogeochemical models that predict greenhouse effect do not adequately consider the complexity of this carbon stock, and model prediction is often at odds with experimental evidence. This model-experiment inconsistency calls for need for an improved understanding of how and to what extent mineral-associated organic carbon is available to microbial decomposition. The ultimate goal of this project is to study the role of clay minerals in mediating microbial decomposition of soil organic matter in response to warming temperature. Various soil organic matter-clay mineral interaction experiments will be performed under well-controlled conditions across a range of temperatures. Experimental data will be used to derive parameters that can be incorporated into biogeochemical models to better predict microbial decomposition of soil organic matter in response to temperature. Reliable predictions of soil carbon turnover are essential to enhanced food security, reduced soil degradation, and mitigation of biodiversity loss. An improved model prediction of future greenhouse emission and environmental change will better enable our society to develop sustainable agriculture and to deal with recently frequent extreme weather and natural disasters.The goal of this proposal is to assess the role of phyllosilicates in mediating the temperature sensitivity of soil organic matter decomposition. The hypothesis posits that soil phyllosilicate minerals control substrate bioavailability and enzyme activity, and thus, by extension, the temperature sensitivity of substrate decomposition in soil. To corroborate this view, investigators propose to integrate mechanistic experimental investigation with innovative biogeochemical (BGC) modeling. They will focus on the ubiquitous phyllosilicates because of their importance in soils and existing knowledge gap. In this one-year demonstration project, they will perform laboratory experiments of enzyme-carbon substrate-mineral interaction (adsorption) experiments. Common soil clay minerals will be used. Organic polymers representing the functionalities of proteins, cellulose, and lignin will be selected as substrate proxies and â-glucosidase, leucine aminopeptidase, and phenol oxidase as enzyme indicators. Kinetic adsorption data will be fitted to derive: 1) the adsorption capacity and affinity of different substrates (and enzymes) onto mineral surfaces; and (2) Vmax and affinity parameters for enzyme-substrate interactions. These parameters and their temperature dependence will be used to parameterize the Equilibrium Chemistry Approximation kinetics. An improved BGC model will reduce uncertainty in current predictions of the response of soil organic carbon stocks to ongoing warming temperature. In addition of regular data dissemination through student involvement, publications, and presentations, results will be incorporated into courses. Content-specific video clips will be exhibited in museums. All investigators will make efforts to visit under-represented K-12 schools to deliver general science lectures and lead various science activities.