Photodegradation effects are related to precipitation amount, precipitation frequency and litter traits in a desert ecosystem

•UV radiation (UV) increased decomposition rate, with higher increase in low lignin litters.•UV photodegradation effects (UVE) depend on precipitation, with higher UVE under low amount and low frequency.•UVE increased with increasing lignin loss during decomposition.•UV decreased microbial total PLFAs, and altered microbial community.

Photodegradation due to litter exposure to solar UV radiation (UV) is presumed to contribute to the surprisingly fast decomposition in some arid and semi-arid regions; however, precipitation may affect the relative importance of photodegradation versus microbial decomposition in litter decomposition. To assess the dependence of photodegradation effects on precipitation, we subjected litters from three plant life forms (spring annual, summer annual and shrub) to two UV treatments (UV block and sunlight) combining four precipitation treatments (two frequencies plus two amounts) over 2.5 years. UV radiation increased k, and it interacted with litter type, with the strongest stimulating effects on low lignin content litter. Precipitation amount and frequency both affected k, and UV photodegradation was dependent on precipitation, with the strongest photodegradation effects in low frequency and low amount of precipitation. UV radiation decreased microbial PLFAs, and altered microbial community in two litters by depressing fungi development. High precipitation frequency significantly increased microbial PLFAs in E. oxyrrhynchum litter. Litter decomposition rate was negatively correlated with initial lignin concentration, and UV photodegradation effects increased with increasing lignin loss, suggesting that the increased decomposition rate under UV radiation may primarily result from photochemical mineralization of lignin, rather than from facilitation of microbial decomposition. Our results demonstrate that UV radiation plays an important role in desert litter decomposition. The dependence of photodegradation on litter type and precipitation underscores the importance of incorporating UV radiation-induced C release into modeling of C cycling in desert ecosystems.