The dynamic changes of solar radiation have received wide attention in global change studies, but there are controversies about the influence of diffuse radiation on ecosystem carbon sequestration. Using eddy covariance measurements from 2010 to 2012, the effects of sky conditions extracted from adjacent sunny, cloudy, and overcast days on net ecosystem productivity (NEP) of a subtropical coniferous plantation were examined from half-hourly to daily scales. Half-hourly NEP responded to the changing radiation more efficiently on overcast days compared to sunny days, but such response did not differ obviously between cloudy and sunny days. Compared with sunny conditions, apparent quantum yield (α) under overcast (cloudy) conditions changed 282.4% (41.7%) in spring, 140.3% (−4.2%) in summer, 218.5% (38.9%) in autumn, and 146.2% (0.5%) in winter, respectively; annually, α under overcast (cloudy) conditions increased by 225.9% (19.8%) in 2010, 189.8% (6.0%) in 2011, and 159.5% (21.4%) in 2012, respectively. Moreover, the potential NEP at the light intensity of 150 and 750 W m⁻² was improved due to increased diffuse fraction. However, both daytime NEP and daily NEP were significantly lower under overcast skies than under sunny and cloudy skies. Compared with sunny days, daily NEP on overcast days decreased by 127.7% in spring, 126.4% in summer, 121.8% in autumn, and 100.6% in winter, respectively; annually, daily NEP decreased by 122.5% in 2010, 141.7% in 2011, and 109.9% in 2012, respectively. Diurnal patterns of daily NEP were quite similar between sunny and cloudy days. Both path analysis and multiple regression showed that solar radiation, especially diffuse radiation, was responsible for the variations of NEP under different skies across seasons, but this effect may be weakened by seasonal droughts. This study implies that the effects of sky conditions on NEP are timescale dependent and should be paid more attention in ecosystem carbon cycle study.

太阳辐射的动态变化在全球变化研究中受到了广泛关注，但是关于扩散辐射对生态系统碳固存的影响存在争议。使用2010年至2012年的涡度协方差测量，从半小时到日尺度，研究了从相邻的晴天，阴天和阴天提取的天空条件对亚热带针叶人工林净生态系统生产力（NEP）的影响。与晴天相比，半小时NEP在阴天对辐射变化的响应更有效，但是在阴天和晴天之间这种响应没有明显差异。与晴天相比，表观量子产率（ α）在春季（多云）下春季变化282.4％（41.7％），夏季变化140.3％（−4.2％），秋季变化218.5％（38.9％），冬季变化146.2％（0.5％）; 每年，在阴天（多云）条件下，α分别在2010年增加225.9％（19.8％），2011年增加189.8％（6.0％）和2012年增加159.5％（21.4％）。此外，在150和750 W m ^-2的光强度下的潜在NEP由于扩散分数的增加而改善。但是，在阴天下，白天NEP和每日NEP均显着低于晴天和阴天。与晴天相比，春季阴天的日NEP分别降低了127.7％，夏季的126.4％，秋季的121.8％和冬季的100.6％。每年，每日NEP分别在2010年，2011年和2011年和2012年分别下降122.5％，141.7％和109.9％。在晴天和阴天之间，每日NEP的昼夜模式非常相似。路径分析和多元回归研究表明，太阳辐射，尤其是漫辐射，是造成整个季节不同天空下NEP变化的原因，但这种影响可能会因季节性干旱而减弱。这项研究表明，天空条件对NEP的影响是时标性的，在生态系统碳循环研究中应引起更多重视。