Decomposition of plant organic matter plays a key role in the terrestrial biogeochemical cycles. Sunlight, as the essential energy for the biogeochemical cycling, can directly break down natural organic matter and accelerate decomposition through photodegradation, accelerating decomposition even in forest ecosystems where understorey solar irradiance remains relatively low. However, it is uncertain how carbon (C) and nitrogen (N) dynamics respond to fluctuations in solar spectral irradiance caused by canopy structure (understorey vs. gaps) and season (open vs. closed canopy phenology). It limits our assessment and prediction of key processes in forest ecosystems in response to climate change. 

WANG Qingwei from the Institute of Applied Ecology, Chinese Academy of Sciences (CAS) conducted a large appropriate spectral attenuation experiment, collaborating with a couple of senior ecologists. They calculated the contribution of solar spectral irradiance to C and N dynamics in the understorey and an adjacent gap created by a clear-cut in a temperate deciduous forest.  

Key findings are that photodegradation, driven by blue light, contributed more to the loss of C and lignin in the gap over the experimental period, while that by UV-B radiation dominated in the understorey prior to and during spring canopy flush. N was immobilized in the understorey during canopy flush before the canopy completely closed, but swiftly released during canopy leaf-fall (Fig.1).  

“It is the first to show that photodegradation plays an important role in lignin decomposition and N dynamics modulated by canopy structure and phenology. Including such effects would improve estimates of biogeochemical cycling in forests responding to changes in climate and land-use.” said Dr. Hiroko Kurokawa from the Forestry and Forest Products Research Institute (FFPRI), Japan.  

This study has been published in Science of the Total Environment entitled " Canopy structure and phenology modulate the impacts of solar radiation on C and N dynamics during litter decomposition in a temperate forest ".  

This research was financially supported by the CAS Young Talents Program, the National Natural Science Foundation of China (NSFC), the Japan Society for the Promotion of Science (JSPS), and LiaoNing Revitalization Talents Program.  

Fig.1 The contribution of solar spectral irradiance to litter C, N and lignin dynamics in the understorey and an adjacent gap in a temperate deciduous forest (Image by WANG Qingwei).