SOIL O2 AND CO2 REVEAL CONTROLS ON SOIL RESPIRATION AND CALCITE FORMATION IN FIELD-BASED EXPERIMENTS

A detailed understanding of the processes that control organic and inorganic carbon cycling in soils is required to address modern day challenges such as mitigating anthropogenic depletion of global soil carbon stocks. An improved understanding of the factors that affect soil carbon cycling will also inform paleosol derived environmental reconstructions, such as constraining the seasonal bias of soil carbonate formation. Yet there are inherent difficulties in studying organic and inorganic soil carbon cycling in modern soils. These difficulties include the heterogenous nature of soils, standing carbon stocks typically integrate hundreds to thousands of years of accumulation, and making continuous and detailed measurements belowground is rife with challenges. Paired high-precision measurements of soil pore space gas concentrations in the field is a potential way to overcome these challenges, as these data are spatially integrative and reflect active soil carbon cycling. Specifically, the pairing of high precision CO₂ and O₂ measurements enables respiration signals to be separated from other processes such as calcite dissolution and formation.

For this study, we designed and installed a long-term automated field-based soil monitoring station in central Texas to investigate the short-term and seasonal controls on soil respiration and soil calcite accumulation. We will present daily high precision soil CO₂ and O₂ data as well as associated soil physical data such (soil moisture, soil temperature, rainfall, etc.) across multiple depths from soils experimentally amended with pulverized calcite and carbonate-free control soils. These data indicate calcite dissolution occurs throughout the year after rainfall events, but its formation is concentrated during the spring months (March through June). During these months, the calcite dissolution signal typically persists for less than 48 hours before the onset of calcite formation, which is consistent with previously published laboratory results. The formation signal can extend for as long as 11 consecutive days, but typically terminated earlier by subsequent rainfall events.