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

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 CO2. 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 O2 measurements in a laboratory potted soil experiment that respiration rates after watering were similar in control and carbonate treatment soils. However, CO2 concentrations were up to 72% lower in the carbonate treatment soil because CO2 was initially consumed during calcite dissolution. Subsequently, CO2 concentrations were over 166% greater in the carbonate treatment soil as respiration slowed and calcite precipitated, releasing CO2. Elevated δ13C values of soil CO2 (>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 CO2 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. Plain Language Summary Carbon dioxide can be removed from the atmosphere by plants and stored in soils. Respiration in soils can later return it to the atmosphere. Measuring how much carbon dioxide is returned to the atmosphere is important for soils in water‐limited locations, because they may control how much carbon is stored in terrestrial environments from year‐to‐year. This measurement is complicated because the dissolution and formation of calcite, a mineral commonly found in arid soils, can also change the amount of soil carbon dioxide. We conducted a laboratory experiment with two soils, one containing calcite and one without calcite to study how calcite affects soil carbon dioxide. Our results show that calcite effects can be identified by simultaneously measuring the amount of carbon dioxide and oxygen present in soils. After a simulated rainfall, calcite di