A considerable fraction of soil-respired CO(2) is not emitted directly to the atmosphere

Soil CO(2) efflux (F(soil)) is commonly considered equal to soil CO(2) 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 CO(2) efflux/O(2) influx, known as the apparent respiratory quotient (ARQ), enables new insights into CO(2) losses from R(soil) not previously captured by F(soil). We present the first study using continuous ARQ estimates to evaluate annual CO(2) 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 CO(2) production in other connected processes within the critical zone.