The Obscuring Effects of Calcite Dissolution and Formation on Quantifying Soil Respiration

Abstract

Abstract Drylands occupy nearly 40% of the land surface and comprise a globally significant carbon reservoir. Dryland‐atmosphere carbon exchange may regulate interannual variability in atmospheric CO 2 . Quantifying soil respiration rates in these environments is often complicated by the presence of calcium carbonates, which are a common feature of dryland soils. We show with high‐precision O 2 measurements in a laboratory potted soil experiment that respiration rates after watering were similar in control and carbonate treatment soils. However, CO 2 concentrations were up to 72% lower in the carbonate treatment soil because CO 2 was initially consumed during calcite dissolution. Subsequently, CO 2 concentrations were over 166% greater in the carbonate treatment soil as respiration slowed and calcite precipitated, releasing CO 2 . Elevated δ 13 C values of soil CO 2 (>6‰ higher in the treatment than control) confirm that observed differences were due to calcite dissolution. These findings demonstrate that calcite dissolution and precipitation can occur rapidly enough to affect soil gas compositions and that changes in soil CO 2 are not always directly related to changes in soil respiration rates. Studies of local soil respiration rates and carbon exchange are likely to be influenced by dissolution and precipitation of calcium carbonates in soils. We estimate that one fifth of global soil respiration occurs in soils that contain some amount of soil carbonate, underscoring the need to account for its obscuring effects when trying to quantify soil respiration and net ecosystem exchange on a regional or global scale.