水杉人工林细根解剖结构和菌根侵染研究

林木根系是地下生态系统中最为复杂的部分之一,其高度异质性是关系到根系生态功能研究结果准确性与可比性的主要因素。为明晰水杉细根的界定范围,探讨水杉细根形态与解剖结构之间的关系,为未来的细根研究提供基础数据,笔者对水杉不同根序等级细根解剖结构与菌根侵染状况进行了研究。结果表明:水杉根系按根序法分级更为合理,并将水杉1、2级根定义为细根,1、2级根表皮完整、皮层较厚、皮层层数较多,3、4级根无表皮和皮层或仅残留少量皮层细胞,随根序等级增加,细根皮层层数和皮层厚度显著降低。随根序增加,周皮木栓化程度增加,维管组织发育逐渐完善,维管组织直径不断增大,维管组织与根系直径的比值(维根比)不断增大,细根直径主要与维管组织直径具有显著的相关性(1级根除外),与皮层薄壁细胞直径、皮层层数之间并无相关性。水杉1～3级根均可观察到菌根侵染现象,随根序等级升高菌根侵染率下降,不同根序等级细根单个个体根系的真菌侵染面积存在明显差异。在未来的细根研究中,应该将细根形态调查与解剖结构特征相结合以确定根序等级和直径的对应关系,进而确定细根的划分范围。

Study on fine root anatomical structure and mycorrhizal colonization in Metasequoia glyptostroboides plantation

Tree root system is one of the most complex parts of the underground ecosystem. The accuracy and comparability in root ecological function studies is limited by highly heterogeneous morphology and structure. The reasonability of definition on fine roots of Metasequoia glyptostroboides was discussed which could improve fine root studies in the future. We determined fine root anatomical structures and root mycorrhizal colonization with different orders in M. glyptostroboides plantation and explored the relationship between fine root morphology and anatomy. We found: firstly, it was more reasonable to classify the roots by root order, and 1,2 level roots were defined as fine roots; secondly,1,2 level roots were those ones with intact epidermis, thicker and multi-layered cortex, and 3, 4 level roots were skinless roots or only a small amount of residual epidermal cells, with root orders increased, roots cortex layers and epidermis thickness became significantly lower; thirdly, with the root order increasing, the degree of cork periderm was significantly increased, vascular tissue development was gradually improved, the diameter of the vascular tissue and the ratio of vascular tissue to root diameter(V/R)was increasing with root order increase. There were significant correlation(except root level)between fine root diameter and vascular tissue diameter, but there was no correlation between fine root diameter and the cortical parenchyma cells diameter or cortical layers; fourthly,the mycorrhizal colonization in 1-3 order roots could be observed, and with root order increase, the mycorrhizal colonization rate was significantly decreased. There were obvious differences in fungal infestation area of single individual root with different order. In the future study, we should combine fine root morphology investigation and anatomy characteristics to investigate the correspondence between the root order and root diameter, and then determine the division of the range of fine roots.