人工授力杨树重金属富集木形成机理的研究

The mechanism of formation of heavy metal accumulated wood is the theoretical foundation of the control of soil pollution, the improvement of wood quality as well as the promotion of ecological efficiency of artificial forest and utilization of timber. It is also the international hot spot and the most difficult field of the interdisciplinary research of wood science and environmental science. In this project, Poplar (Populusdeltoids cv. I-69/55) is chosen, which is widely accepted as a model tree for dendroremediation of Cadmium(Cd). Looking at the whole tree while focusing on the stem, the study is conducted the first time domestically and in the world from the perspective of comparison of normal wood and tension wood. The real processes of the accumulation of Cd in the two kinds of living poplar wood are simulated by planting seedlings in pots with soils containing various ranges of Cd concentrations. In addition, the pots are placed upright for normal wood while tilted for tension wood with a 45° angle. The growth properties and microstructure of normal and tension wood, the content and distribution of Cd in different parts of the tree stem, in different types of cells, and in the cell wall, are monitored and analyzed continually for 4 years. The objectives are to make clear the relationships between the variation of content and distribution of Cd in different wood cells and growth properties, anatomy, microstructure and cell wall characteristics, and to discover the Cd transportation path, accumulating position and affecting factors. Thus, the mechanism of the formation of Cd accumulated wood can be revealed. This study is a new extension of woody environmental science, which has important scientific significance and application values.

重金属富集木形成机理的研究是利用速生树种治理重金属污染，改良木材品质，提高人工林培育生态效益和木材利用率的理论基础，同时也是木材科学和环境科学等多学科交叉前沿国际研究热点和难点。本项目拟以国内外公认富集重金属Cd的模式树种杨树（Populus deltoids cv. I-69/55）为对象，着眼全树，聚焦树干，国内外首次从正常木和人工授力应拉木比较的角度，通过配置不同浓度Cd土壤盆栽苗木，直立和倾斜45°放置来模拟杨树正常木和应拉木富集重金属的全过程，在木材宏观、显微和超微水平上，连续4年跟踪研究杨树不同部位、不同类型细胞和不同层次细胞壁富集重金属Cd含量和分布的演化规律及其与生长特征、木材宏观、微观和超微构造之间关系，探明生长过程中杨树富集重金属Cd的运输通道，固着位置和影响因子，从而揭示杨树重金属富集木形成机理。该研究是我国木质环境学研究的拓展和外延，具有重要的科学意义和应用价值。

人工林速生杨树不仅是重要的林木资源，而且能够吸收和治理土壤中的重金属Cd。杨树重金属Cd富集木形成机理的研究是利用速生树种治理Cd污染，改良木材品质，提高人工林培育生态效益和木材利用率的理论基础，同时也是木材科学和环境科学等多学科交叉的前沿研究课题。本项目以69杨（Populus deltoids cv. I-69/55）为研究对象，通过配置不同浓度Cd土壤来盆栽苗木，直立和倾斜45°放置来模拟杨树正常木和应拉木富集重金属的全过程，研究杨树不同部位、不同细胞Cd含量的分布和重金属Cd富集木的形成机理。研究结果表明: 1)不同浓度（0,5,20,50,100 mg/kg）处理下直立和倾斜生长69杨对土壤中的Cd有很强耐受性，四年生直立生长的杨树的平均树高和地径分别比人工倾斜杨树高12.81%和5.41%。2)随着杨树的生长和土壤中Cd含量的增加，直立和倾斜生长杨树各部分的Cd含量均显著增加，直立和倾斜杨树总体表现为树叶＞树皮＞树根＞树枝＞树干，三年生倾斜杨树应拉木的Cd含量比直立正常木高27.88%。3)杨树木材纤维长度和双壁厚随土壤中Cd的处理浓度具有显著性差异，而导管长度、微纤丝角和结晶度等差异不显著；倾斜生长对导管长度的影响显著,导管形态会随着倾斜生长而变化，从而影响Cd在导管内的累积和迁移。4)木材中导管、木纤维、木射线、细胞壁纹孔以及树皮筛管细胞上都存在Cd分布，在直立生长正常木木纤维、导管和木线中Cd的平均比例分别为49%、33%和18%，而倾斜生长应拉木中平均比例分别为41.26%、33.96%和24.78%，均表现为木纤维>导管>木射线。5)土壤中的重金属Cd先进入树根和树干木材导管中，导管中的Cd一部分通过导管与木纤维和木射线上的具缘纹孔或半具缘纹孔对储存在木纤维和木射线细胞中，同时一部分会沿着导管向上迁移，经过树枝最后到达树叶，同时一部分会沿着木射线进行横向运输，达到树皮部分，树叶和树皮中Cd的相对含量较多，而树干生物量大，导管、木纤维、木射线细胞数量较多，树干中累积的Cd绝对含量最多。本结果可为Cd污染土壤的修复治理和速生杨树综合利用提供理论依据和科学方法。