ORE-CZ: Ecohydrological Controls on Soil Respiration and the Apparent Respiratory Quotient Across a Dynamic Storage Gradient

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Soils contain more carbon than vegetation and the atmosphere combined, and soil respiration describes the transfer of soil carbon to the atmosphere via plant roots and microbes. As air temperatures rise and water availability changes, changes in the soil respiration flux represent significant potential feedback to the greenhouse effect and the magnitude of future warming. Accordingly, this project will take advantage of soil carbon dioxide (CO2) and oxygen data provided by the NSF-funded Dynamic Water Critical Zone (CZ) Thematic Cluster to quantify the variability of soil respiration and the fate of soil-produced CO2 with respect to changes in soil development, vegetation, and topography that mediate water availability across representative semi-arid montane elevation and climatic gradients. The research will support career training and learning experiences for graduate and undergraduate students at California State University, Chico, which is a federally designated Hispanic-Serving Institution (HSI), a Primarily Undergraduate Institution, and where more than 50% of the student population are first generation college students. A “bedrock to treetop” CZ approach considers feedbacks between soil, water, landscape position, and living organisms at Earth’s surface. Dynamic water storage - water with intermediate residence times - sustains CZ function between precipitation events, and is critically important to soil respiration and carbon cycling. As a result, the main objective of this research is to quantify the importance of dynamic water storage to the integral CZ functions of soil respiration and the Apparent Respiratory Quotient (ARQ) that determines the degree to which soil-produced CO2 is respired directly to the atmosphere versus transported laterally or vertically with infiltrating water. The investigators will specifically test the hypotheses that (1) soil respiration and the ARQ will be proportional to the volume of dynamic water storage in the root zone, and (2) that dynamic water storage capacity will interact with complex terrain to determine the variability of soil respiration and ARQ over space and time. Because research activities will be replicated and integrated across multiple watersheds, they will allow for evaluation of the transferability of process-based information, toward a more comprehensive understanding of CZ carbon cycling with direct implications for the climate change mitigation potential of semi-arid montane ecosystems. This project was supported with co-funding of the HSI Program which aims to enhance undergraduate STEM education, broaden participation in STEM, and build capacity at HSIs. Achieving these aims, given the diverse nature and context of the HSIs, requires innovative approaches that incentivize institutional and community transformation and promote fundamental research (i) on engaged student learning, (ii) about what it takes to diversify and increase participation in STEM effectively, and (iii) that improves our understanding of how to build institutional capacity at HSIs.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.