Foliar litter chemistry mediates susceptibility to UV degradation in two dominant species from a semi-arid ecosystem

Aims Abiotic processes such as photodegradation play important roles in litter decomposition in semi-arid ecosystems. However, little is known about whether UV degradation responds similarly to factors controlling biotic decomposition rates, such as soil moisture and plant litter chemistry. Here, we evaluated the relative importance of UV degradation versus biotic decomposition in contrasting precipitation regimes for two species. Methods We manipulated ultraviolet (UV) radiation under two rainfall treatments (ambient and added precipitation) and measured decomposition rates of leaf litter from two abundant species in a southern California coastal sage scrub ecosystem: a native shrub (Salvia mellifera) and an exotic annual grass (Avena fatua). Results The influence of UV radiation exposure on decomposition did not vary with rainfall treatment, and UV radiation exposure only increased litter mass loss of the A. fatua litter, not S. mellifera. This pattern was driven by accelerated loss of hemicellulose and cellulose litter fractions when the exotic grass litter was exposed to UV radiation. The greatest influence of UV radiation was observed after 18 months. Conclusions The sensitivity of hemicellulose and cellulose litter fractions to UV radiation suggests that shifting plant species composition which results in altered litter chemistry could change ecosystem sensitivity to UV photodegradation.