Predictions based on factors such as climate and litter chemistry tend to underestimate measured rates of litter decomposition in arid and semi-arid grassland ecosystems. We hypothesized that ultraviolet (UV) radiation plays a large role in the decomposition process in these systems via photodegradation. We designed a factorial experiment of UV radiation and litter chemistry at three contrasting sites that represent arid, semi-arid, and mesic grassland ecosystems. We predicted that photodegradation may increase decomposition in the arid sites more than the mesic site. At each site, we placed litterbags filled with 2 contrasting litter types under louvered screens that either block or pass UV radiation. After 2.5 and 6 months of decomposition, we measured mass loss, changes in litter chemistry, microbial biomass, and extracellular enzyme activity. During this time period, we observed significant increases in mass loss with UV exposure. The effect of UV radiation was similar in all three sites and in both litter types. Differences among sites were also similar in both UV-exposed and unexposed litter. This suggests that while UV radiation does play a role in decomposition, it may not account for the more rapid than expected mass loss observed in arid systems during early stages in the decomposition process.
