Litter decomposition in hyper-arid deserts: Photodegradation is still important.

Photodegradation due to litter exposure to solar UV radiation is presumed to contribute to the surprisingly fast decomposition in some arid and semi-arid regions; however, few studies have directly examined photodegradation effects in hyper-arid regions (annual precipitation <150mm) and its dependence on precipitation. Three litters with different initial qualities (low vs high C:N) were decomposed under full spectrum sunlight (UV radiation) and UV filtering from solar radiation at three sites with contrasting precipitation amounts (144mm, 76mm and 16mm) for 2.5years. UV radiation increased mass loss and litter decomposition rates by 23-70%. UV photodegradation effects (UVE) on litter decomposition rate differed among experimental sites, with significantly stronger effects in less arid sites (144mm and 76mm) than more arid site (16mm). High-quality litter (low C:N ratio) showed the fastest decomposition rate, and UVE was also affected by litter quality, but no consistent trend was observed. Litter N loss was greatest in full sunlight and the linear relationships between C and N contents was not changed by UV filtering over time. UV radiation increased C loss of all fractions, and hemicellulose and cell solubles showed significant contributions to litter mass loss. Our findings suggest that UV photodegradation can increase mass loss and nutrient release by the positive priming effects on microbial decomposition in hyper-arid regions, although UVE differed among three sites with contrasting precipitation amounts.