Disentangling the rates of carbonyl sulfide (COS) production and consumption and their dependency on soil properties across biomes and land use types

Abstract

Abstract. Soils both emit and consume the trace gas carbonyl sulfide (COS) leading to a soil–air COS exchange rate that is the net result of two opposing fluxes. Partitioning these two gross fluxes and understanding their drivers are necessary to estimate the contribution of soils to the current and future atmospheric COS budget. Previous efforts to disentangle the gross COS fluxes from soils have used flux measurements on air-dried soils as a proxy for the COS emission rates of moist soils. However, this method implicitly assumes that COS uptake becomes negligible and that COS emission remains steady while soils are drying. We tested this assumption by simultaneously estimating the soil COS sources and sinks and their temperature sensitivity (Q10); these estimates were based on soil–air COS flux measurements on fresh soils at different COS concentrations and two soil temperatures. Measurements were performed on 27 European soils from different biomes and land use types in order to obtain a large range of physical–chemical properties and identify the drivers of COS consumption and production rates. We found that COS production rates from moist and air-dried soils were not significantly different for a given soil and that the COS production rates had Q10 values (3.96 ± 3.94) that were larger and more variable than the Q10 for COS consumption (1.17 ± 0.27). COS production generally contributed less to the net flux at lower temperatures but this contribution of COS production increased rapidly at higher temperatures, lower soil moisture contents and lower COS concentrations. Consequently, measurements at higher COS concentrations (viz. 1000 ppt) always increased the robustness of COS consumption estimates. Across the range of biomes and land use types COS production rates co-varied with total soil nitrogen concentrations (r = 0.52, P<0.05) and mean annual precipitation (r=0.53, P<0.05), whilst the gross COS uptake rate and the first-order COS hydrolysis rate constant co-varied significantly with the microbial biomass nitrogen (N) content of the soils (r=-0.74 and 0.64, P<0.05 and P<0.05, respectively). Collectively our findings suggest a strong interaction between soil nitrogen and water cycling on COS production and uptake, providing new insights into how to upscale the contribution of soils to the global atmospheric COS budget.