In the past few years, carbonyl sulphide (COS or OCS) has emerged as a new promising trace gas to estimate gross primary productivity (GPP, that is how much carbon plants can remove from the atmosphere, check this if you want to know more). This approach is based on the assumption that COS only enters the vegetation and does not come out. However, this is hard to test on plants where gas exchange is controlled by responsive surface pores (stomata) that open and close in response to for example light. Here, we used plants that lack those pores to test for fluxes of COS coming in (and out) coupled to photosynthetic carbon removal. In this paper, we separate uptake from emission an the influence of temperature and light on two commonly distributed bryophytes in temperate habitats, one moss (Scleropodium purum) and one liverwort (Marchantia polymorpha). To our surprise, we found out that in bryophytes, COS does not only come in, but it is also emitted and those emissions were controlled by temperature. Read the whole story, on open access here.