太阳辐射对长白山阔叶红松林净生态系统碳交换的影响

 太阳辐射是植物进行光合作用的前提条件, 因此成为影响植被吸收大气CO₂的重要环境因子。该研究基于30 min通量和常规气象数据, 以相对辐射和晴空指数为指标, 分析了2003~2006年生长旺季(6~8月)太阳辐射的改变对长白山阔叶红松(Pinus koraiensis)林净生态系统碳交换(Net ecosystem exchange, NEE)的影响。结果表明: 天空有一定云层的覆盖对阔叶红松林碳的净吸收有明显的促进作用。4年里6~8月间生态系统最大光合速率在天空有云覆盖时较晴空条件下分别提高了34%、25%、4%和11%。在晴空指数约为0.5的中等辐射条件下, 该生态系统的NEE达到最大。对生态系统碳的净吸收有促进作用的临界相对辐射约为37%, 而使该生态系统NEE达到最大的最适相对辐射约为75%。进一步分析表明, 天空云量的增多和云层厚度的增加会引起散射辐射比例的增加、大气温度和水汽亏缺程度的降低等环境效应, 由此可能会导致冠层光合作用的增加和地上部分呼吸的减弱, 从而共同决定了净生态系统碳吸收作用的增强。

EFFECTS OF SOLAR RADIATION ON NET ECOSYSTEM EXCHANGE OF BROADLEAVED-KOREAN PINE MIXED FOREST IN CHANGBAI MOUNTAIN, CHINA

Aims Solar radiation can affect net ecosystem exchange (NEE) of carbon dioxide of forests, because cloud cover alters solar radiation, which in turn alters other environmental factors such as temperature and vapor pressure deficit. Our objective was to analyze the effects of these changes on NEE of broad-leaved-Korean pine (Pinus koraiensis) mixed forest in Changbai Mountain. Methods Our analysis was based on 30-min flux data and routine meteorology data for mid-growing season (June to August) for 2003–2006. Important findings Cloud cover significantly increased NEE. The light-saturated maximum photosynthetic rate was enhanced 34%, 25%, 4% and 11% on cloudy days compared with clear days in the four years of study. Relative irradiance and clearness index (k_t) were important in quantifying the effects of cloud cover, cloud shape and cloud thickness on solar radiation. When kt was about 0.5, NEE reached its maximum. When the relative irradiance was over the critical relative irradiance of 37%, NEE was enhanced; maximum NEE occurred at about 75%. Enhancement of NEE was ascribed to increased canopy assimilation and decreased above-ground respiration, which resulted from increased diffuse radiation and decreased air temperature and vapor pressure deficit with increased cloudiness.