A considerable fraction of soil-respired CO₂ is not emitted directly to the atmosphere

Soil CO₂ efflux (F_soil) is commonly considered equal to soil CO₂ production (R_soil), and both terms are used interchangeably. However, a non-negligible fraction of R_soil can be consumed in the subsurface due to a host of disparate, yet simultaneous processes. The ratio between CO₂ efflux/O₂ influx, known as the apparent respiratory quotient (ARQ), enables new insights into CO₂ losses from R_soil not previously captured by F_soil. We present the first study using continuous ARQ estimates to evaluate annual CO₂ losses of carbon produced from R_soil. We found that up to 1/3 of R_soil was emitted directly to the atmosphere, whereas 2/3 of R_soil was removed by subsurface processes. These subsurface losses are attributable to dissolution in water, biological activities and chemical reactions. Having better estimates of R_soil is key to understanding the true influence of ecosystem production on R_soil, as well as the role of soil CO₂ production in other connected processes within the critical zone.