关键词: 细根, 解剖结构, 干旱瘠薄山地, 耐旱策略, 生态适应

Abstract:

Objective: To explore the anatomical characteristics of fine roots of trees under drought environments, and to reveal the ecological strategies of trees adapted to drought stress. Method: Fine roots were sampled from eleven tree species in a 4 hm² plot which was established in 2011 in the hilly mountainous areas in central parts of Shandong province. Anatomical structures (root diameter, cortex thickness, vascular cylinder (stele) diameter, vessel inner diameter, and the density of vessels) of 2 475 samples of roots from the first to the third order were measured via microscopy imaging system and paraffin sectioning. One-way ANOVA was conducted to compare differences in the anatomical characteristics among the tree species, and Principle Component Analysis (PCA) was performed to group the tree species. Result: The diameter of fine roots of the 11 tree species increased with root orders in general. The diameter, cortex thickness, vascular cylinder (stele) diameter of the fine roots within the same root order was significantly different among species (P < 0.05). Gleditsia sinensis has the largest cortex thickness of the first and the second order roots whereas Clerodendrum trichotomum and Morus alba have the smallest. Cotinus coggygria has the largest stele diameter in the third order roots; Melia azedarach has the largest vessel inner diameter. Pistacia chinensis has the smallest stele diameter and vessel inner diameter; P. chinensis has the largest root vessel density. PCA analysis showed that the first component explained 46% of variation in fine root anatomical traits representing absorptive functions, and the second component summarized 38% of variation in fine root anatomical traits responsible for transportation. PCA analysis grouped the 11 tree species into three groups based on anatomical features of fine roots, with the first group possessing a smaller root diameter, thinner cortex and more compacted transportation tissues (including 8 tree species such as M. alba, P. chinensis), the second having a smaller root diameter and thinner cortex, but looser transportation tissue (including C. coggygria and M. azedarach), and the third group showing a larger root diameter, thicker cortex and more compacted transport tissue (only including G. sinensis). Conclusion: Anatomical structure of fine roots reflected their adaptation to arid habitats. The eleven species displayed two strategies to adapt to the drought conditions: one was fast uptake and rapid transportation of water, and another was efficient finding and rapid transportation of water. The two strategies have their own advantages in different soil conditions. Nine tree species showed their adaptation to drought via improving water absorptive capabilities. Some trees with fast water uptaking and rapid transportation, such as M. alba and P. chinensis, demonstrating more suitability for habitats with long-term drought, seasonal rainfall and thin soil layer. Some species with efficient water finding and rapid water transport, such as G. sinensis, are more suitable for the habitats with long-term drought and thick soil layer. The anatomical traits of fine roots determine the strategies of trees adapted to drought environment. The root cortex thickness and vessel properties in fine roots are important indicators of assessing the capability of trees adapting to dry soils, this would provide a theoretical basis for species selection for afforestation in arid infertile mountainous areas.

Key words: fine roots, anatomical structure, arid and infertile mountain area, drought tolerance strategies, ecological adaptation