Impacts of Changes in Solar Radiation on Terrestrial Gross Primary Productivity of China

Solar radiation at the Earth's surface affects gross primary productivity (GPP) of terrestrial ecosystems. Changes in cloud cover or atmospheric aerosol loadings affect both the global solar radiation and the diffuse component, and consequently affect terrestrial GPP. In this study, we used a two-leaf light use efficiency model (TL-LUE), which differentiates the differences of upper and lower leaves in receiving direct and diffuse radiation, to estimate the terrestrial GPP of China from 1981 to 2012 and to assess the impacts of changes in global solar radiation and diffuse fraction on terrestrial GPP. The averaged annual national GPP in China during 1981-2012 was 6.78 Pg C yr-1. The averaged annual global solar radiation has a significant decreasing trend (2.18 MJ m-2 yr-1, p<0.05) from 1981 to 2012, causing the averaged annually GPP to reduce by 0.13 Pg C yr-1, while the diffuse radiation fraction has a significant increasing trend (0.2% 10a-1, p<0.05) in this period, causing the averaged annually GPP to increase by 0.06 Pg C yr-1. It is essential to differentiate the response of GPP to variations in direct and diffuse radiation for assessing the impact of solar radiation change on the terrestrial carbon cycle.