Abstract
Solar radiation significantly affects terrestrial gross primary productivity (GPP). However, the relationship between GPP and solar radiation is nonlinear because it is affected by diffuse radiation. Solar radiation has undergone a shift from darker to brighter values over the past 30 years in China. However, the effects on GPP of variation in solar radiation because of changes in diffuse radiation are unclear. In this study, national global radiation in conjunction with other meteorological data and remotely sensed data were used as input into a two-leaf light use efficiency model (TL-LUE) that simulated GPP separately for sunlit and shaded leaves for the period from 1981 to 2012. The results showed that the nationwide annual global radiation experienced a significant reduction (2.18 MJ m−2 y−1; p < 0.05) from 1981 to 2012, decreasing by 1.3% over this 32-year interval. However, the nationwide annual diffuse radiation increased significantly (p < 0.05). The reduction in global radiation from 1981 to 2012 decreased the average annual GPP of terrestrial ecosystems in China by 0.09 Pg C y−1, whereas the gain in diffuse radiation from 1981 to 2012 increased the average annual GPP in China by about 50%. Therefore, the increase in canopy light use efficiency under higher diffuse radiation only partially offsets the loss of GPP caused by lower global radiation.
Highlights
Carbon sequestration is extremely important for global change studies [1]
Terrestrial gross primary productivity (GPP), which indicates the ability of vegetation to use light energy through fixation of carbon dioxide during photosynthesis, is a primary component of the terrestrial carbon cycle [2]
We modeled the effects on GPP of solar radiation variation caused by changes in diffuse radiation in China over the period 1981–2012 using a two-leaf light use efficiency model (TL-LUE), which was driven by national global radiation in conjunction with other meteorological data and remotely sensed data
Summary
Carbon sequestration is extremely important for global change studies [1]. Terrestrial gross primary productivity (GPP), which indicates the ability of vegetation to use light energy through fixation of carbon dioxide during photosynthesis, is a primary component of the terrestrial carbon cycle [2]. Global radiation (Rg) includes both direct and diffuse components. Higher Rd increases the canopy light use efficiency (LUE) and leads to the enhancement of GPP [4,5,6,7]. Under cloudy or severe haze conditions, even if Rg decreased, vegetation GPP can increase as a result of the higher Rd component. An increase in Rd results in enhanced canopy LUE and leads to an increase in vegetation productivity. Gu et al [8] confirmed that canopy LUE under Rd was higher than that under direct radiation for six vegetation types. Gu et al [9] observed that after a volcanic eruption, changes in Rd on the GPP of Harvard Forest increased by 3–21% because of the increase in the diffuse radiation fraction
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