Modeling grassland and forest biogeochemistry with MEMS 2.0

Our new ecosystem model, MEMS 2.0, was built on the soil organic matter (SOM) model, MEMS 1.0. In MEMS 2.0, we extended the one-layer soil module of MEMS 1.0 to a whole soil profile with SOM simulated in all soil layers. Soil water and temperature, which are the most influential environmental factors on decomposition, are modeled for each layer. We added a plant growth submodel to represent grass and tree production and their litter inputs into the soil. Nitrogen is modeled in all SOM pools, plant organs, and mineral nitrogen pools. The model simulates three measurable litter pools: soluble, hydrolyzable, and unhydrolyzable; and two measurable SOM pools: particulate and mineral-associated organic matter (POM and MAOM). In MEMS 2.0, we incorporated updated understandings of relevant processes including distinct pathways of POM and MAOM formation, microbial-mineral relationships, dynamic microbial carbon use efficiency, point of entry, SOM saturation kinetics and in vivo versus ex vivo MAOM contributions. Here, we will present results from the calibration and testing of MEMS 2.0 using measurements in both topsoil and subsoil from several grassland and forest sites in the U.S, and discuss how modeling SOM as POM and MAOM pools better represents the formation, persistence, and functioning of SOM across contrasting ecosystems.