Decomposition of organic material contributes 60 Gt of carbon dioxide into the atmosphere annually. Climate scientists have focused their attention on quantifying the mechanisms responsible for the breakdown of litter. Photodegradation, or the breakdown of organic matter via solar radiation, has recently been identified as having a significant effect on decay rates. We examined the effects of solar ultraviolet radiation on decomposition of cattail (Typha angustifolia). Litterbags were placed in a standing position that either transmitted or attenuated ultraviolet-B radiation (UV-B; 280-320 nm) in an emergent marsh in Southern Minnesota. We sampled litter every 60 d for three collection periods over the winter of 2015.
Litter that received ambient UV-B lost more mass towards the end of the experiment (120 and 180 d). Litter in UV-B treatments lost 12.7% of the initial mass, compared to 7.0% under the UV-B attenuating filters. Litter decay constants (k) ranged from 0.15 to 0.37 and were greater under the UV-B treatments. In addition, we examined concentrations of bulk-soluble phenolics and cell-wall constituents (cellulose, hemicellulose and lignin) as well as total carbon and nitrogen. Contributions to mass loss appeared to be mainly attributed by differences in cellulose and hemicellulose concentrations between treatments. Litter under UV-B treatments lost 8% more cellulose and hemicellulose than those under UV-B attenuating filters. There were no observed differences in lignin, solubles, ash or C:N. Our results suggest that ultraviolet radiation can influence decomposition of standing wetland biomass over the winter months. Further research will examine the effects of litter position and microbial contributions to decomposition.