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We studied the effects of elevated CO 2 (180 -200 ppmv above ambient) on growth and chemistry of three moss species (Sphagnum palustre, S. recurvum and Polytrichum commune) in a lowland peatland in the Netherlands. Thereto, we conducted both a greenhouse experiment with both Sphagnum species and a field experiment with all three species using MiniFACE (Free Air CO 2 Enrichment) technology during 3 years. The greenhouse experiment showed that Sphagnum growth was stimulated by elevated CO 2 in the short term, but that in the longer term ( ‡1 year) growth was probably inhibited by low water tables and/or downregulation of photosynthesis. In the field experiment, we did not find significant changes in moss abundance in response to elevated CO 2 , although CO 2 enrichment appeared to reduce S. recurvum abundance. Both Sphagnum species showed stronger responses to spatial variation in hydrology than to increased atmospheric CO 2 concentrations. Polytrichum was insensitive to changes in hydrology. Apart from the confounding effects of hydrology, the relative lack of growth response of the moss species may also have been due to the relatively small increase in assimilated CO 2 as achieved by the experimentally added CO 2 . We calculated that the added CO 2 contributed at most 32% to the carbon assimilation of the mosses, while our estimates based on stable C isotope data even suggest lower contributions for Sphagnum (24 -27%). Chemical analyses of the mosses showed only small elevated CO 2 effects on living tissue N concentration and C/N ratio of the mosses, but the C/N ratio of Polytrichum was substantially lower than those of the Sphagnum species. Continuing expansion of Polytrichum at the expense of Sphagnum could reduce the C sink function of this lowland Sphagnum peatland, and similar ones elsewhere, as litter decomposition rates would probably be enhanced. Such a reduction in sink function would be driven mostly by increased atmospheric N deposition, water table regulation for agricultural purposes and land management to preserve the early successional stage (mowing, tree and shrub removal), since these anthropogenic factors will probably exert a greater control on competition between Polytrichum and Sphagnum than increased atmospheric CO 2 concentrations.

This paper presents the setup and pressure calibration of an 800-ton multi-anvil apparatus installed at the Vrije Universiteit (Amsterdam, the Netherlands) to simulate pressure-temperature conditions in planetary interiors. This high-pressure device can expose cubic millimeter sized samples to near-hydrostatic pressures up to~10 GPa and temperatures exceeding 2100°C. The apparatus is part of the Distributed Planetary Simulation Facility (DPSF) of the EU Europlanet 2020 Research Infrastructure, and significantly extends the pressure-temperature range that is available through international access to this facility.

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Raman spectrometry is a powerful technique for the rapid identification of most minerals and organic chemicals without sample preparation. In this context, the European Space Agency (ESA) and NASA selected a Raman spectrometer in the payload of the future ExoMars and Mars 2020 missions to identify organic compounds and mineral products indicative of biological activity on Mars. Little is known, however, about the effects of Mars atmospheric conditions on instrument performance and on the Raman spectra. The objective of this study was to i) design and construct a versatile simulation chamber to reproduce the atmospheric conditions expected inside a rover on Mars, ii) to test the performance of a previously designed breadboard miniaturized Raman laser spectrometer (RLS) inside the chamber. The Mars Atmosphere Simulation Chamber (MASC) is a temperature and atmosphere controlled chamber. It includes an innovative heating-cooling system to create homogeneous temperatures inside the chamber that can be varied between 243 K and 283 K, while the charged coupled device (CCD) of the Raman spectrometer can be independently cooled (e.g., 233 K). A vacuum and gas control system permits evacuation of the chamber and the subsequent introduction of any (dried) gas mixture at partial pressures between 1 mbar and several bars. The minimum CCD temperature was found to depend on the surrounding MASC temperature and atmosphere. A vertical shift of 3 pixels on the CCD was observed for the Raman signals upon lowering the temperature from 283 to 253 K. We show that the RLS instrument gives reliable Raman spectra over the tested range of temperatures and from a vacuum of 4 x 10 −5 mbar to a CO 2 atmosphere at pressure relevant to Mars (8 mbar). For example, the Raman spectra of three test minerals, calcite, aragonite and baryte, showed identifiable Raman peaks with Raman shift values within ± 1 cm −1 of those reported in previous works under terrestrial conditions. This confirms that a RLS instrument is useful for the identification of minerals during future missions to Mars; once a necessary detector recalibration was carried out, the system performed well under 8 mbar pressure and 243-283 K. The MASC was found to be a versatile instrument; it can provide important information on instrument performance under Martian conditions and other temperatures and atmospheric conditions can also be simulated.