Search

Litter decomposition contributes to one of the largest fluxes of carbon (C) in the terrestrial biosphere and is a primary control on nutrient cycling. The inability of models using climate and litter chemistry to predict decomposition in dry environments has stimulated investigation of non-traditional drivers of decomposition, including photodegradation, the abiotic decomposition of organic matter via exposure to solar radiation. Recent work in this developing field shows that photodegradation may substantially influence terrestrial C fluxes, including abiotic production of carbon dioxide, carbon monoxide and methane, especially in arid and semi-arid regions. Research has also produced contradictory results regarding controls on photodegradation. Here we summarize the state of knowledge about the role of photodegradation in litter decomposition and C cycling and investigate drivers of photodegradation across experiments using a meta-analysis. Overall, increasing litter exposure to solar radiation increased mass loss by 23% with large variation in photodegradation rates among and within ecosystems. This variation was tied to both litter and environmental characteristics. Photodegradation increased with litter C to nitrogen (N) ratio, but not with lignin content, suggesting that we do not yet fully understand the underlying mechanisms. Photodegradation also increased with factors that increased solar radiation exposure (latitude and litter area to mass ratio) and decreased with mean annual precipitation. The impact of photodegradation on C (and potentially N) cycling fundamentally reshapes our thinking of decomposition as a solely biological process and requires that we define the mechanisms driving photodegradation before we can accurately represent photodegradation in global C and N models. © 2012 US Government.

Integrated annual methane fluxes measured from 1994 to 1996 at sites representing specific tundra vegetation and land cover types were weighted areally using a vegetation map [Auerbach et al., 1997] for the Kuparuk River basin and subareas. Wetland and open water CH4 emissions dominate the Kuparuk River basin emission estimate. Areal weighting of site fluxes resulted in a regional CH4 emission estimate of 2.09 x 1010 g CH4 yr-1 for the Kuparuk River basin. The global CH4 emission obtained by extending areally weighted annual fluxes from this study to global tundra area (7.34 x 1012 m2) is 5.83 Tg CH4 yr-1. This is about 15% of the Fung et al. [1991] atmospheric tracer model estimate and indicates that the vegetation distribution of the Kuparuk River Basin is not typical of the entire Arctic. Reconciling results from atmospheric tracer model estimates and areally weighted field flux measurements will require accurate high-resolution circumpolar estimates of wetland and open water areas and fluxes. Copyright 1998 by the American Geophysical Union.