Recent studies showed that photochemical breakdown (photodegradation) of plant material accounts for a substantial portion of litter decomposition and subsequent trace gas release in ecosystems under high radiative load and low pre-cipitation. In the absence of solar radiation, thermal degradation may also cause trace gas release at temperatures below the ignition point. These observations suggest that the abiotic processes of photodegradation and thermal deg-radation of plant litter may be important in understanding global trace gas budgets. In a laboratory incubation study, we performed a simultaneous carbon (C) accounting of CO 2 , CO, and CH 4 produced as a byproduct of photodegra-dation and thermal degradation of six different plant litter types that varied in chemical composition. The patterns of trace gas release during photodegradation and thermal degradation differed considerably across the six plant materi-als, suggesting that chemical composition of litter may influence the rates of abiotic degradation. There was a strong positive correlation between the rates of trace gas release during photodegradation and temperature. A significant portion of trace gases were produced during low temperature (< 100 °C) thermal degradation of litter in the absence of solar radiation, which was also positively correlated to temperature. In addition, both thermal degradation and photodegradation occurred in the absence of O 2 . This indicates that the mechanism formerly accepted as photo-oxi-dation may only be one of several photodegradation processes. We speculate that the direct breakdown of chemical groups such as carboxyl, carbonyl, and methoxyl groups may result in CO 2 , CO, and CH 4 release. We suggest that the combined processes of thermal and photodegradation of litter may be a previously under accounted source of C-based trace gases from terrestrial systems.