Latitudinal responses of litter decomposition to solar radiation.

Photodegradation driven by solar radiation has been confirmed as an important driving factor for litter decomposition. However, previous single-site studies could not quantify the relative contribution of variation in solar radiation to litter decomposition. To address it, we conducted a field experiment in Heshan National Field Research Station of Forest Ecosystem, Guangdong (Heshan Station, south subtropical climate), Jigongshan Ecological Research Station, Xinyang, Henan (Jigongshan Station, north subtropical climate) and Daqinggou Ecological Research Station, Institute of Applied Ecology, Chinese Academy of Sciences (Daqinggou Station, temperate climate) at intervals of 10 degrees. We examined litter decomposition of Populus davidiana and Larix olgensis, two species with significant differences in initial litter quality through an in-situ spectral-attenuation experiment. Treatments included full-spectrum, No-UV-B (attenuating UV-B radiation <315 nm) and No-UV & Blue (attenuating all UV and blue wavelengths <500 nm). After nearly 1-year decomposition, litter dry mass remaining of P. davidiana and L. olgensis under full-spectrum treatment was lowest at Heshan (30.2% and 36.3%), and highest at Jigongshan (37.3% and 45.8%). Among all sites, litter dry mass remaining was lowest under the full-spectrum, and lower than that of No-UV-B and No-UV & blue. UV and blue light significantly increased litter mass loss of P. davidiana and L. olgensis, with contributions of 59.7% and 57.0% (Heshan), 46.4% and 42.1% (Jigongshan), and 39.0% and 45.9% (Daqinggou), respectively. The contribution of UV-A and blue light (315-500 nm) was greater than UV-B (280-315 nm); the cumulative irradiance, soil temperature and moisture were the main driving factors for litter photodegradation.