The role of photo- and thermal degradation for CO<sub>2</sub> and CO fluxes in an arid ecosystem

Abstract

Abstract. Recent studies have suggested the potential importance of abiotic degradation in arid ecosystems. In this study, the role of photo-and thermal degradation in ecosystem CO 2 and CO exchange is assessed. A field experiment was performed in Italy using an FTIR-spectrometer (Fourier Transform Infrared) coupled to a flux gradient system and to flux chambers. In a laboratory experiment, field samples were exposed to different temperatures and radiation intensities.No photodegradation-induced CO 2 and CO fluxes of in literature suggested magnitudes were found in the field nor in the laboratory study. In the laboratory, we measured CO 2 and CO fluxes that were derived from thermal degradation. In the field experiment, CO uptake and emission have been measured and are proposed to be a result of biological uptake and abiotic thermal degradation-production.We suggest that previous studies, addressing direct photodegradation, have overestimated the role of photodegradation and observed fluxes might be due to thermal degradation, which is an indirect effect of radiation. The potential importance of abiotic decomposition in the form of thermal degradation, especially for arid regions, should be considered in future studies.

Soil fluxes of carbonyl sulfide (COS), carbon monoxide, and carbon dioxide in a boreal forest in southern Finland

“…This global mean value is significantly higher than the mean CO uptake (∼ 1 nmol m −2 s −1 ) observed at this boreal forest in the late growing season. Recent field observations of soil CO uptake in temperate ecosystems are also smaller than this global mean, for example, less than 1 nmol m −2 s −1 in a grassland in Italy (van Asperen et al, 2015) and 0.78 nmol m −2 s −1 in a grassland in Denmark (Bruhn et al, 2013). If we assume the soil from this site is representative of boreal forest soils, it follows that temperate and tropical soils must have higher CO uptake capacity to compensate for the relatively low soil CO uptake in the boreal forest compared with the global mean, or the current estimate of global soil CO uptake needs to be revisited.…”

“…Collectively, the sum of COS uptake (or CO uptake) contributions from the ensemble of microbial groups may not show a well-defined temperature response like that in respiration. Although we cannot rule out the possibility that the flux ratio vs. temperature pattern is influenced by divergent temperature responses of microbial uptake and abiotic production (e.g., Whelan et al, 2016;King, 1999;van Asperen et al, 2015), abiotic production is unlikely to correlate with respi- ration. A mechanistic explanation for the temperature dependence of flux ratios requires a clear-cut separation of uptake and production processes and further understanding of the microbial communities involved in COS uptake or CO uptake.…”

“…Soil CO flux is also the net balance between concurrent uptake and production activities (Conrad andSeiler, 1980, 1985;Sanhueza et al, 1998;King, 1999;King and Crosby, 2002;Bruhn et al, 2013;van Asperen et al, 2015;Pihlatie et al, 2016). Soil CO uptake is primarily due to microbial activity (Inman et al, 1971;Conrad and Seiler, 1980;Whalen and Reeburgh, 2001) and involves more diverse metabolic pathways compared with those in COS uptake (Mörsdorf et al, 1992;King and Weber, 2007;Ogawa et al, 2013).…”

“…CO production in soils has been considered largely abiotic (Conrad and Seiler, 1985;Zepp et al, 1997), but microbes on fine roots have also been reported to contribute significantly to CO production in the laboratory (King and Crosby, 2002). Soil CO emissions generally increases with temperature and solar radiation in field conditions (King, 1999;Yonemura et al, 2000a;Zepp et al, 1997;van Asperen et al, 2015), indicating dominant contributions from photochemical and thermal production. It remains poorly understood how environmental factors control the variability of soil CO flux in the field, because most studies on soil CO flux are laboratory incubations of altered soil samples or short-term, sporadic field experiments.…”

“…We explore diurnal and seasonal variabilities of the fluxes and identify the major physical and biological drivers of the variabilities. (Suni et al, 2003;Vesala et al, 2005). The forest floor is covered by mosses (Dicranum polysetum, Hylocomium splendens, and Pleurozium schreberi) and understory herbs including bilberry (Vaccinium myrtillus) and lingonberry (Vaccinium vitis-idaea) (Kulmala et al, 2011).…”