EAGER SitS: Studying soil biotic and abiotic processes through continuous, high-precision monitoring of soil CO2 an O2 concentrations

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Soils are a vital natural resource, the successful management of which depends on the ability to monitor and understand numerous belowground biotic and abiotic processes. These processes, such as mineral weathering and carbon and nitrogen cycling, directly affect soil health. In order to advance our understanding of these soil processes, this research project will combine continuous, high precision monitoring of soil pore space oxygen, carbon dioxide, and ammonia gas concentrations, each of which are affected by these processes, with the development of a computer model. Undergraduate students who identify with underrepresented groups will be recruited to participate in this research project. The research results will help to quantify soils as a carbon source/sink and inform sustainable land management practices aimed at feeding the expanding global population while managing environmental contamination from fertilizers. These results will be disseminated through courses that the PI teaches, in addition to peer-reviewed publications.The respiratory quotient (RQ, moles of CO2 produced per mole of O2 consumed during respiration) is a fundamental indicator of metabolism that we currently cannot monitor in-situ in soils. Learning about soil community RQ and the factors that affect its variability will help to understand microbial metabolisms, controls on autotrophic and heterotrophic respiration rates, and ultimately soil carbon cycling. Therefore, the goal of this research project is to isolate continuously and monitor in-situ the RQ of the soil community. The first step of this research project will be to expand existing soil physics and chemistry models to quantify the effects of diffusion and gas-water exchange on soil gas composition. The effectiveness of these adapted models will be tested using controlled laboratory experiments. The next step will be to calibrate pore space NH3 and O2 concentrations as a measure of nitrification, using laboratory incubations of soils selected for later field-monitoring. This information is required for accurate determination of RQ, because nitrification consumes O2 in addition to that consumed by respiration. The final step will be to measure continuously and in-situ CO2, O2, and NH3 concentrations in natural soils using commercially-available flow-through sensors coupled to a custom-built autosampler. Simultaneous measurement of soil moisture, soil temperature, and relevant meteorological variables will accompany the soil gas monitoring. The expanded soil physics model and the laboratory soil core calibrations will be used to account for diffusion, water-gas exchange and nitrification in order to determine soil community RQ. Variation in soil community RQ through time and space in grassland and forest soils will be investigated. An improved understanding of natural variability in soil RQ will advance 1) understanding of soil biotic processes, such as how metabolisms in soil change temporally and spatially, and 2) the interaction between biotic and abiotic processes, such as those that drive chemical weathering and calcium carbonate dissolution/precipitation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.