湿地松林叶面积指数测算

对湿地松（Pinus elliotii）当年生和多年生两针一束、三针一束叶片的长度、宽度、厚度和重量分别进行量测，据此探讨不同类型叶片的叶形和比叶面积差异，并结合样地调查数据对中科院千烟洲试验站湿地松人工林的叶面积指数进行计算。结果表明：湿地松三针一束叶片合拢后横切面基本呈圆形，当年生叶和多年生叶的平均直径分别为1．688mm和1.706mm；两针一束叶片合拢后从统计学上讲横切面不是圆形，而是椭圆形，叶片厚度方向直径大于宽度方向（当年生叶厚度和宽度方向直径分别为1．580ram和1．422mm，多年生叶分别为1．568mm和1.410mm），但如果把厚度和宽度方向直径的平均值近似成圆柱体直径计算时误差在3％以内；如果只用厚度或宽度方向直径代表平均直径计算结果会有2％。10％的误差；当年生叶和多年生叶、两针一束叶和三针一束叶之间比叶面积差别很大，计算的三种比叶面积（投影比叶面积、圆柱面比叶面积和比表面积）中，当年生叶的比叶面积明显大于多年生叶，三针一束叶片的投影比叶面积和比表面积都大于两针一束叶片，但圆柱面比叶面积恰好相反。湿地松林的叶面积指数若按投影叶面积算为3．61，按圆柱面的外表面算为5．12，按总表面积的一半算为4．52，比利用冠层分析仪测量的结果略大。

Leaf area index measurement of Pinus elliotii plantation

The length,width,thickness and weight of the current year and more than one-year-old needles of both bi-needle-cluster and tri-needle-cluster of slash pine(Pinus elliottii) were measured to expose the differences in terms of leaf shape and specific leaf area(SLA),and leaf area index(LAI) was estimate based on measurement of the plantation in Qianyanzhou Ecological Station.The needle's cross section of tri-needle cluster was approximately in a standard circle.However,cross section of bi-needle cluster was proved to be an ellipsoid.Diameter in thickness direction(1.580mm for 1-year-old needle and 1.568mm for 2-4-year-old needles) was significantly larger than that in width direction(1.422mm and 1.410mm for 1 year old needle and 2-4-year-old needles,respectively).If the cross section of bi-needle was arbitrarily regarded as a circle by using the average diameter of the two directions,there would be an error less than 3%,while the error will be as much as 2%10% if only one of the two diameters is adopted.The correlation between leaf length and leaf area showed that leaf length was significantly related to leaf area.Varied among needle types,SLA of 1-year-old needles showed larger than that of 2-4-year-old needles.Tri-needle leaves have much bigger specific projected area and specific total area than bi-needle leaves,but smaller in specific surface area.The projected LAI of slash pine plantation in Qianyanzhou Ecological Station was 3.61,and the LAI estimated based on the surrounding-surface area and the half of the total surface area of cylinder were 5.12 and 4.52 respectively.All these estimated values of LAI were larger than the direct measurement by optical canopy analysis system.