淮北相山三种群落中优势树种次生木质部的解剖学特征

对淮北相山侧柏、构树混交林6个优势树种次生木质部的观察表明，其结构表现出一定的旱生特征：高的复孔率和导管分布频率，窄导管，木纤维短，射线低。利用相对输导率和脆性指数对导管水分输导的有效性和安全性进行了评估，结果表明6个优势树种的相对输导率依次为：牡荆〉酸枣〉扁担木〉构树〉柘树〉小叶鼠李，脆性指数依次为：构树〉牡荆〉扁担木〉酸枣〉小叶鼠李〉柘树，植物水分输导的有效性和安全性与其在相山的自然分布相一致。作为广布优势树种，牡荆、酸枣和扁担木的次生木质部在导管分子长度、单孔率、导管频率、相对输导率、脆性指数、多列射线高度、多列射线宽度和单列射线高度等性状上均表现出一定的可塑性。与混交林和人工侧柏林相比，灌丛中植物导管分子短，单孔率低，导管频率大，射线低，相对输导率大，脆性指数小，更倾向于旱生特点。逐步多重回归分析表明，随着郁闭度的增加，导管分子长度和单孔率增加。随着风速的增加，导管频率增加。随着土壤含水量的增加，多列射线变宽。

Secondary Xylem Anatomic Characteristics of Dominant Plant Species in Three Communities in Xiangshan Mountain, Huaibei, China

The results of anatomic observations on secondary xylem of 6 dominant species in a Platycladus orientalis + Broussonetia papyrifera mixed forest in Xiangshan mountain,Huaibei,China,indicated that these species share some xeromorphic features in secondary xylem such as high vessel frequency,less percentage of single porous,thinner vessel,shorter fibers,and lower rays.The availability and safety of the vessel associated with water conduction was evaluated through relative conductivity and the vulnerability index,the result shown that relative conductivity of the 6 dominant species is ordered as Vitex negundo var.cannabifolia,Ziziphus jujuba var.spinosa,Grewia biloba var.parviflora,Broussonetia papyrifera,Cudrania tricuspuidata,Rhamnus parvifolia,while the vulnerability index is ordered as B.papyrifera,V.negundo var.cannabifolia,G.biloba var.parviflora,Z.jujuba var.spinosa,C.tricuspuidata,R.parvifolia,and the availability and safety of water conduction of these plants is coincided with their distribution in Xiangshan mountain.The three widely distributed dominant species,Z.jujuba var.spinosa,V.negundo var.cannabifolia and G.biloba var.parviflora,show great plasticity in some characters,including vessel element length,vessel frequency,relative conductivity,vulnerability index,percentage of single porous,multiserate ray height,multiserate ray width,and single ray height,etc.Compared to those in mixed forest and P.orientalis forest,the species in shrub tend to have shorter vessel elements,higher vessel frequency,less single porous percentage,lower rays,higher relative conductivity,and less vulnerability index,thus indicated that they are inclined to more xeromorphic anatomically.The result from the stepwise multiple regressions show that both of the vessel element length and percentage of single porous increased with the canopy density,and the vessel frequency increased with the wind velocity,multiserate ray width increased with the soil water content.