荆条灌丛孤立冠层下不同位置冠层的叶面积指数和透光率分析

Leaf area index and light transmittance at different positions under isolated Vitex negundo var. heterophylla canopy

利用LAI-2200植物冠层分析仪(PCA)测定荆条灌丛孤立冠层的叶面积密度(LAD)、叶面积指数(LAI)和冠层开度(DIFN),研究孤立荆条灌丛下3个测点、5个方位LAD、LAI和DIFN的变化规律,分析透光率及其变化规律。结果表明:1)冠层北点的LAD、LAI均稍大于南点,DIFN均较小,说明对天空辐射的遮蔽都较大。2)对正午太阳直接辐射的影响表现为:DIFN以茎基南侧最大,冠层北缘次之,茎基北侧最小,说明南点虽然叶面积指数较大,但太阳直接辐射的透光率却最好;夏至日冠层北缘的透光率最大,茎基南侧点次之,茎基北侧点最小,春秋分日,茎基南侧点最大,冠层北缘次之,茎基北侧点最小。3)荆条灌丛下太阳直接辐射日变化的分析表明:东、西的透光率较大,东南、正南、西南透光率相当;夏至日的DIFN中午前后比早晨和傍晚偏高。研究结果不仅为孤立灌丛下太阳直接辐射透光率的分析方法提供参考,而且为荆条灌丛下不同位置遮荫效果和冠下实生苗造林时播种位置的确定提供科学依据。

The paper measured leaf area density （LAD）,leaf area index （LAI）,and diffuse noninterceptance （DIFN） of Vitex negundo var.heterophylla canopy using LAI-2200 canopy analyzer （PCA）,and then analyzed the measured data of three measuring points in five directions.The results showed that：1） LAD and LAI of the northern part point under canopy were a little greater than those of southern part point under canopy and DIFNs of the two measuring points were both low,suggesting that the canopies had great shielding effect; 2） At the sun light direction at noon time,DIFN of southern part point under canopy was greatest,followed by that of the northern edge point of canopy,and the least was at the northern part point under canopy,indicating that the transmittance of direct solar radiation at the southern part was high though LAI there was great.At the summer solstice,DIFN of the northern edge point of canopy was greatest,followed by the southern part point under canopy,and the least was at the northern part point under canopy; at the vernal equinox and autumnal equinox,DIFN of the southern part point under canopy was greatest,the northern edge point of canopy was in the second place,and the least was at the northern part point under canopy; 3） The result of daily variation of direct solar radiation at the northern edge of V.negundo var.heterophylla showed that：light transmittance at east and west parts were greater,and those at southeast,south,and southwest were roughly the same; around the summer solstice,DIFN at the noon was greater than that in the morning and evening.This paper provides solar direct radiation transmittance measurement method under isolated shrubs canopy,and at the same time it provides the shielding effect at different positions under V.negundo var.heterophylla canopy and sets up scientific basis for determination of appropriate seeding position of afforestation under V.negundo var.heterophylla canopy.