Soil COS exchange: a comparison of three European ecosystems

The potential of carbonyl sulfide (COS) flux measurements as an additional constraint for estimating the gross primary production (GPP) depends, among other preconditions, on our understanding of the soil COS exchange and its contribution to the overall net ecosystem COS flux. We conducted soil chamber measurements of COS, with transparent chambers, in three different ecosystems across Europe. The in situ measurements were followed by laboratory measurements of soil samples collected at the study sites. The soil samples were exposed to UV radiation to investigate the role of photo‐degradation for COS exchange. In situ and laboratory measurements revealed pronounced inter‐ and intra‐site variability of COS exchange. In situ COS fluxes were primarily governed by radiation in the savannah‐like grassland (SAV), soil temperature and intra‐site heterogeneity in the deciduous broadleaf forest (DBF) and soil water content (SWC) and intra‐site heterogeneity in the evergreen needleleaf forest (ENF). The soil of the ecosystem with the highest light intensity incident on the soil surface, SAV, was a net source for COS, while the soils of the other two ecosystems were COS sinks. UV radiation increased COS emissions and/or reduced COS uptake from all soil samples under laboratory conditions. The impact of UV on the COS flux differed between soil samples, with a tendency towards a stronger response of the COS flux to UV radiation exposure in samples with higher SOM content. Our results emphasize the importance of photo‐degradation for the soil COS flux and stress the substantial spatial variability of soil COS exchange in ecosystems.