Mechanistic soil biogeochemistry modeling confronted with reality
Long-standing gaps in soil biogeochemistry modeling include the (i) partitioning of soil organic carbon (SOC) into its functional pools, (ii) the representation of microbial biomass and diversity, and (iii) the mechanistic coupling of carbon and nutrient cycles. Existing studies of these components are typically limited to soil column scale or to effects on global soil organic carbon, but they are rarely evaluated at ecosystem scale. A new soil biogeochemistry module linked with a well-tested land-surface and terrestrial biosphere model (T&C) is introduced. The soil biogeochemistry module explicitly separates different litter pools and partitions SOC into particulate, dissolved, and mineral fractions. Extracellular enzymes and microbial pools are explicitly modelled and differentiated based on the functional roles of bacteria, and saprotrophic and mycorrhizal fungi (including explicit plant-mycorrhizal interactions). Soil macro-fauna is also modeled. The model considers the cycles of nitrogen, phosphorous and potassium, in addition to carbon. The model is applied to 20 sites spanning a wide range of climatic conditions and different biomes, and is challenged to reproduce (i) global patterns of microbial biomass including community composition and SOC components, (ii) the responses to litter manipulation experiments, and (iii) ecosystem response to nitrogen addition. Model simulations compared favorably with global patterns of microbial and macro-faunal biomass relations with soil organic carbon, soil respiration, and Net Primary Production (NPP). The predicted long-term responses of soil carbon pools to litter manipulation are in ranges similar to experimental results. The model predicts that fine roots, bacteria, fungal and macro-faunal respiration account, respectively, for 33%, 40%, 24% and 3% of total belowground respiration on average, despite large site-to-site variability. Root exudation and carbon export to mycorrhizal fungi represent about 13% of plant NPP. The results offer general and mechanistically-derived estimates of microbial biomass and its contribution to respiration fluxes and to soil organic matter dynamics.
Dr. Simone FATICHI, ETH, Zürich Switzerland
Date and schedule: 14th May 2019 15:00 to 17:00
Venue: LIST - 41, rue du Brill L-4422 BELVAUX