Abstract: In recent years, it has recognized that photodegradation possibly plays a key role in litter decomposition. This paper summarized the action mechanisms of photodegradation, roles of photodegradation in carbon and nutrient cycling, relationships between photodegradation and microbial decomposition, and factors affecting photodegradation. Photodegradation has both positive and negative effects on litter decomposition. The positive effects lie in the photolysis and photooxidation of organic matter, leading to the changes of litter chemistry, fragmentation, and facilitation to leaching, whereas the negative effects are related to the inhibition of microbial decomposition induced by strong light radiation. The CO₂ produced by the photochemical mineralization in the process of photodegradation is the main mechanism of the C loss from ecosystems. Besides UV, the blue and green light-wave bands in visible light can affect litter photodegradation. The photodegradation is affected by water status, litter chemical properties, and litter exposed area. It was suggested that the related research priorities in the future could be the research methods of photodegradation, the interactions between photodegradation and environmental factors, the spatial variance of photodegradation, and the relationships between photodegradation and microbial decomposition in the process of litter decomposition.

Key words: SARS, Coronavirus, Gene recombination, Life evolution, Combined pollution