Rose Abramoff and a group of mostly Millennials (with a few of us old farts included as well) have published a paper describing a new model structure of soil carbon dynamics based on current process-level understanding. The CENTURY and RothC models, which have been with us since the 1980s, have served us well to assess the impacts of changing inputs of carbon from plant litter in both agronomic and native ecosystems, but they rely on a few hypothetical soil “pools” based on turnover times and first order kinetics. This assumption makes the models computationally efficient, but these soil C pools are difficult, if not impossible, to actually measure. The new Millennial Model defines soil C pools that can be measured (albeit imperfectly and with some challenges), and its functions represent the most important microbial processes of C transformation, chemical processes of substrate quality, and physical processes of protection and stabilization of organic matter on mineral surfaces and within soil aggregates. Although presented with equations and preliminary parameterizations, the Millennial Model is still largely a conceptual model and awaits a challenge with field data. However, it is a refreshing and thought-provoking piece of research, and I was proud and honored to be on a team with such talented young scientists.
Conceptual model diagram of the Millennial (top) and Century models (bottom). The black boxes are carbon pools, and the colored boxes are fluxes. Solid arrows indicate the direction of each flux. The color legend indicates edaphic, biological, and climatic factors that may modify the rate of a given flux. Dash lines indicate controls (i.e., microbial biomass regulates the depolymerization rate):