基于细根解剖特征的树种耐旱性解析

The arid-tolerance of trees based on the anatomical characteristics of fine roots

树种选择是干旱瘠薄山地水土保持和植被修复的关键。研究树种细根解剖特征是探讨在干旱生境下树种的适应策略并开展树种选择的前提。以鲁中南干旱瘠薄山地常见的10个造林树种为对象,测定了树种不同根序细根的剖面直径、皮层厚度、维管柱(中柱)直径、维根比、导管直径及导管密度等,对比分析了细根解剖结构的差异性,以期为该区域水土保持和植被修复树种选择提供理论依据。研究发现:针叶树种(黑松、侧柏)1级根细根直径显著大于落叶树种;落叶型灌木细根直径较小,且种间差异不显著(P<0.05)。细根维管柱直径的变化规律与细根平均直径的变化规律相似。落叶型灌木1~2级细根皮层厚度较大。随着根序的增加,各树种导管直径也随之增大。落叶型灌木的导管直径小于乔木,落叶型乔木导管直径较其他树种更大。导管密度与根直径的变化规律相反。依据细根解剖特征将10个树种聚为3类:第1类为皮层薄、输导组织致密型;第2类为皮层薄、输导组织疏松型;第3类皮层厚、输导组织疏松型。

[Background] The selection of tree species is critical for the soil and water conservation and vegetation restoration in arid-barren mountainous areas. There are 40% areas in Shandong province belonging to mountain area,where water is one of important environment factors limiting vegetation restoration. Thus,it is very important to choose tree species with developed roots. The examination on the anatomical characteristics of tree roots would be helpful for the tree species selection. [Methods]The study site is located in Xueye county of Laiwu city,belonging to typical arid-barren mountainous areas of Shandong province. After afforestation,ten common tree species were selected and all the roots of trees for each species were sampled. According to the branching orders,the roots were grouped into five classes,and root traits（ i. e.,the root diameter,cortex thickness,stele diameter,ratio of vascularcylinder to root diameter,vessel diameter,and vessel density） were examined by paraffin sectioning,Nikon Eclipse E200 microscopy and Scope Image 9. 0 software. The differences of root anatomical traits among tree species were analyzed and clustered by One-way ANOVA and SPSS 19. 0 with Excel.[Results]The fine root diameter of tree species increased with the root order. The first order roots showed larger diameter in conifer trees than in those deciduous trees. The diameters of deciduous shrub roots were smaller than those arbor and vines; however,the difference among species was not significant（ P 0. 05）. The stele diameters of fine roots demonstrated similar changes with the average diameter of fine roots. The cortex thickness of the first and second order roots in the deciduous trees was large.However,the root vessel diameter of all the tree species increased with the increase of root order,the vessel diameters in vines roots（ i. e.,Lonicera japonica and Euonymus fortunei） were smaller than those in arbors and shrubs roots. The vessel diameters in deciduous trees were larger than those of other tree species. The changes of vessel density were opposite to that of root diameter. Based on the anatomical characteristics of fine roots,the 10 species were clustered into three categories,the first one was the thin cortex and compacted transport tissue,including L. japonica,Lespedeza bicolor,Vitex negundo var.heterophylla,Amorpha fruticosa and Pinus thunbergii; the second one was the thin cortex and loose transport tissue, including E. fortunei, Cotinus coggygria, Robinia pseudoacacia and Platycladus orientalis; the third one was the thick cortex and loose transport tissue,including Gleditsia sinensis.[Conclusions]The anatomical structure of tree root in arid habitat is related to its life type,which is the ecological adaptability in the process of long-term tree species evolution. Root＇s anatomical structure is a key index to explore the survival strategy of tree species in drought stress environment.