鼎湖山针阔混交林光合有效辐射的时空格局

Temporal and spatial distribution of photosynthetically active radiation flux of coniferous and broadleaved mixed forests at the Dinghushan Mountain,low subtropical China.

光合有效辐射（PAR）是影响生态系统能量转化和物质生产的重要生态因子，对其时空格局的研究，有助于深入理解生态系统的生理生态因子变化和光合行为．该文分析了2003年鼎湖山南亚热带针阔混交林生态系统PAR通量的时空分布特征及相互关系．结果表明，在日尺度上，PAR在进入冠层内部的过程中，其强度不断减弱，变异系数（CV）则不断增大；各层次PAR月总量的年变化均呈单峰形，并分别于7月和3月达到最大值和最小值．雨季和旱季，各层次PAR的日均变化均呈单峰曲线，其中冠层上方（PAR1）和乔木第1亚层（PAR2）呈规则的单峰曲线，而乔木第3亚层（PAR，）和灌木及草本层（PAR．）则为不规则的单峰曲线；旱季各层次PAR的平均值为雨季的68．99％～71．48％；旱季各层次PAR日通量的CV非常接近，而雨季PAR，和PAR．的CV则明显增加．全年PAR1、PAR2、PAR3和PAR4总量分别为1842．27、1374．37、471．38和288．39MJ/m^2，各占下行短波辐射（RSd）的40．07％、29．89％、10．25％和6．27％．全年PAR：、PAR，和PAR．的相对光合有效辐射分别为74．6％、23．6％和15．7％．在日尺度和月尺度上PAR。与RSd均呈极显著直线相关，而RSd的系数远小于通常的范围（0．44～0．50）．

PAR （photosynthetically active radiation） is an important ecological factor which controls the energy transforming and matter production. It is very helpful to understand the physio-ecological factors and photosynthesis to research the temporal and spatial characteristics of PAR flux of the ecosystem. The temporal and spatial distribution of PAR of the coniferous and broadleaved mixed forests at the Dinghushan Mountain, low subtropical China, was analyzed in 2003 in this paper. The results were as the followings： the intensity of daily PAR reduced and the variation coefficients （CV） increased, when PAR came into the ecosystem. The curves of monthly total PAR for each forest layer presented a single peak in a year. The maximum and minimum PAR values of each layer .appeared in July and March respectively. The diurnal changes of average PAR were just like single peak types both in rainy season and dry season. The PAR above the canopy （ PAR, ） and that in the first arbor layer（ PARz ）presented a normal peak type curve, but it was not with the third arbor layer（ PARs ）and forth arbor layer（ PAR, ）. The average PAR values in dry season were about 68.99%- 71.48% of those in wet season. The CV values of daily PAR flux for each layer were very similar in dry season, but those of PARs and PAR4 became dramatically higher in wet season. The annual PAR, , PAR2, PARs and PAR4 were 1 842.27, 1 374.37, 471.38 and 288.39 MJ/m^2 respectively, about 40.07%, 29.89 %, 10.25 % and 6.27 % of downweUing shortwave solar radiation （ Rsd ） respectively. The RPFD （relative photosynthesis photon flux density） of PAR2, PARs and PAR, were 74.6% ,23.6% and 15.7% respectively. An obviously significant linear correlation existed between the daily and monthly PAR, and Rsd . The coefficients of Rsd were less than the usual values, which ranges from 0.44 to 0.50.