SGER: An Experimental System to Study Belowground C Fluxes in Soils

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Belowground carbon pools and fluxes in terrestrial ecosystems have received much attention in global change research. Globally, soils are a significant carbon pool containing more carbon than the atmosphere. This proposal focuses on two key processes involving belowground carbon that are still relatively poorly understood, viz. soil respiration and inorganic carbon transformations. Uncertainties with regard to these processes originate, in large measure, from the inability to separate biotic processes (root and microbial respiration) from abiotic processes (gas transport and CaCO3 transformations) and difficulties in measuring root respiration rates in situ. These uncertainties will be addressed by building an artificial root system simulating belowground respiration. In the proposed project two hypotheses will be tested: 1) short-term increases in soil respiration after precipitation events are predominantly regulated by surface microbial processes because changes in soil diffusivity, gas displacement and root respiration rates are too slow to account for rapid responses as observed in the field, and 2) CaCO3 precipitation and dissolution are directly dependent on belowground biological activity and will therefore predominantly occur around root surfaces. The heart of this proposal is a novel artificial root system, which will be constructed using perforated tubing connected to a CO2 supply. By adjusting the flow rate of CO2, the root respiration rates will be fixed and known Broader impacts of this SGER award include the development of a novel approach to obtain a better mechanistic understanding of belowground processes that can be applied to a wide range of questions relevant to terrestrial ecology. The study complements ongoing research at the Desert Research Institute and will enhance its research capabilities. The experimental system can act as an important tool for teaching students fundamentals of gas transport in heterogeneous environments and help students understand the interaction between biological and physical processes. One graduate student will be supported to work on this project.