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