The role of photo- And thermal degradation for CO2 and CO fluxes in an arid ecosystem

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 CO2 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 CO2 and CO fluxes of in literature suggested magnitudes were found in the field nor in the laboratory study. In the laboratory, we measured CO2 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. 1 Introduction CO2 is the main carbon species being exchanged between biosphere and atmosphere and the most important anthropogenic greenhouse gas. CO is a less abundant nongreenhouse gas but considered important in the climate debate due to its oxidation process with atmospheric OH (Stocker et al., 2013). Yearly, terrestrial ecosystems exchange approximately 120 Pg of carbon with the atmosphere (Stocker et al., 2013). Arid ecosystems account for approximately 40% of land area and 20%of the soil carbon pool but are still an unknown factor in climate models (Lal, 2004). In recent studies, the possible importance of abiotic degradation for arid regions, such as photo- And thermal degradation, has been recognized (Austin and Vivanco, 2006; King et al., 2012; Rutledge et al., 2010).