西双版纳热带季节雨林光合有效辐射的垂直分布格局和季节动态

Vertical distribution pattern and seasonal dynamics of photosynthetically active radiation in a tropical seasonal rain forest, Xishuangbanna

光合有效辐射(PAR)是植物初级生产力的主要控制因子,对森林生态系统结构、功能和动态等都有重要的影响。本研究分析了西双版纳热带季节雨林不同群落层次(林冠上方77.7 m、乔木上层61.3 m、乔木中层24.3 m、乔木下层16 m和幼灌层2 m)、不同季节(雨季、旱季)PAR的变异特征,并结合混合线性模型解析了影响PAR分布特征的关键因子。结果表明:(1)各层次PAR旱季和雨季的日动态变化趋势基本一致,最大值均出现在正午前后,且旱季PAR略大于雨季。(2)各层次PAR月最大值多出现在旱季的干热期(3—4月),最小值多出现在旱季的多雾期(11—2月)。(3)各层PAR年总量分别为林冠上方7533.63 mol·m^(-2)、乔木上层5327.93 mol·m^(-2)、乔木中层1346.69 mol·m^(-2)、乔木下层1036.87 mol·m^(-2)、幼灌层58.63 mol·m^(-2),旱季和雨季的占比接近。由于受到不同程度的遮挡,乔木上层、乔木中层、乔木下层和幼灌层的PAR年总量分别占全光照的70.72%、17.88%、13.76%和0.78%。(4)混合线性模型的结果表明,时间因素(时刻、季节)和空间因素(森林群落上一冠层的PAR)均在一定程度上影响着群落内各层次的PAR。在西双版纳热带季节雨林中,PAR进入森林内部后随林冠深度的增加逐级递减,形成了复杂多样的光环境,孕育了丰富的生物类群。

Photosynthetically active radiation(PAR) is a main factor controlling primary productivity, which influences the structure, function and dynamics of forest ecosystems. Here, we analyzed the variations of PAR in different community layers(77.7 m of above canopy, 61.3 m of upper canopy, 24.3 m of middle canopy, 16 m of lower canopy, and 2 m of shrub layer) and different seasons(rainy season and dry season) in a tropical seasonal rain forest of Xishuangbanna. The key factors affecting the distribution of PAR were determined using linear mixed model. Results showed that:(1) The diurnal dynamic trends of PAR in various vertical layers were generally similar in both seasons, with the maximum value appearing around noon, and PAR in the dry season was slightly higher than that in the rainy season.(2) The maximum monthly PAR in various vertical layers usually appeared in the dry-hot period(March to April) of the dry season, while the minimum mostly appeared in the fog-cool period of the dry season(November to December).(3) The annual total amount of PAR in the above canopy, upper canopy, middle canopy, lower canopy, and shrub layer were 7533.63, 5327.93, 1346.69, 1036.87 and 58.63 mol·m^(-2), respectively, which was roughly equally distributed between dry season and rainy season. Due to different degrees of shading, the annual total amount of PAR in upper canopy, middle canopy, lower canopy and shrub layer accounted for 70.72%, 17.88%, 13.76% and 0.78% of the total, respectively.(4) The results of mixed linear model showed that both temporal factor(hour, season) and spatial factor(PAR of the upper canopy) affected the PAR of each subsequent layer in the community. PAR gradually decreased toward the forest floor, which subsequently created a complex light environment and sustained diverse groups of organisms in the tropical seasonal rain forest in Xishuangbanna.