太阳辐射变化对亚热带人工常绿针叶林总初级生产力影响的模拟分析

Modelling the effects of changes in solar radiation on gross primary production in subtropical evergreen needle-leaf plantations

太阳辐射是陆地生态系统碳水循环的能量来源。太阳辐射的变化对植被吸收大气CO2具有重要影响。该文通过辐射观测数据建立散射辐射比例与晴空指数的关系,结合生态过程模型(BEPS)和通量观测数据,模拟分析了太阳辐射变化对千烟洲常绿针叶林总初级生产力(GPP)的影响。研究结果表明:千烟洲森林生态系统的阴叶对年GPP总量的贡献达67%,太阳辐射变化对阴叶光合作用的影响决定了冠层GPP的变化;太阳辐射强度和分布的年际差异导致年GPP对太阳辐射变化的响应不同,2003、2004和2005年太阳辐射分别变化–5.44%、–1.83%和6.26%,可使千烟洲生态系统当年GPP总量达到最大值;在季节上,太阳辐射的增加会导致5–6月GPP上升,7–9月GPP下降,使年GPP变化程度降低;在天尺度上,晴空指数在0.43时,太阳辐射变化对GPP的影响最小。

Aims Solar radiation is the energy source of terrestrial ecosystem carbon and water cycles. Observation shows that solar radiation has experienced noticeable variations in recent decades and significantly impacted on plant photosynthesis. Our objective was to investigate the impacts of changes in solar radiation on gross primary production （GPP） at the Qianyanzhou eddy tower site in subtropical forest in China. Methods We first established the relationship between diffuse radiation fraction and clearness index based on the observed solar radiation and diffuse radiation data. Then, a two-leaf ecological process model, the Boreal Ecosystem Productivity Simulator （BEPS）, was used to simulate the impacts of different changes in solar radia- tion on shaded GPP, sunlit GPP, and canopy GPP in the typical subtropical evergreen needle-leaf plantations. Important findings Results showed that the effects of changes in solar radiation on shaded leaves predominantly determined the changes in the canopy photosynthesis as the shaded leaves contributed 67% to the total GPP. The impacts of changes in solar radiation on GPP varied inter-annually due to variations in the intensity and distribution of solar radiation from year to year. The GPP during 2003-2005 reached maximum when the solar radiation changed by -5.44%, -1.83%, and 6.26% in each year, respectively. Increased solar radiation enhanced the GPP during May and June, but reduced the GPP from July through September. The shaded leaves responded to changes in radiation differently in different seasons, and the sunlit and shaded leaves had different responses in the same season. Consequently, there were patterns of apparent offset in the total GPP and reduced sensitivity to changes in solar radiation on an annual basis. The changes in solar radiation had the smallest impact on GPP when the cleamess index was at 0.43.