镉胁迫下杞柳对金属元素的吸收及其根系形态构型特征

Abstract

采用水培方法,研究了杞柳(<em>Salix integra</em>)2个品种在0-90 μmol/L Cd处理下不同组织对Cd的吸收和积累规律,探讨了镉胁迫下杞柳根系形态学功能响应特征以及对矿质离子吸收的影响。结果发现,镉在杞柳2个品种不同组织的含量均表现为根>韧皮部>木质部>叶。2个品种地上部组织对镉的吸收和积累规律相似:在0-70 μmol/L Cd处理浓度范围内,随着溶液Cd浓度的增加,叶、木质部、韧皮部中镉的含量逐渐增加,到50 μmol/L时,镉在地上部组织的含量达到最高,当Cd处理浓度达90 μmol/L时,地上部各组织中Cd含量出现下降趋势。而2个品种根系对Cd的吸收则不同,"微山湖"品种在溶液Cd达70 μmol/L时,根系镉的积累量最大,在90 μmol/L时,根系Cd的积累量明显下降;"一枝笔"品种根系在0-90 μmol/L范围内,根系Cd的积累量均为增加趋势。通过分析2个品种根系形态学参数变化发现,Cd胁迫抑制了杞柳2个品种根的伸长,促进了"微山湖"品种根的径向生长,导致根系平均直径增加;进一步对叶片矿质营养状态分析发现, Ca、Mn的吸收受镉胁迫的影响较大,在高浓度镉胁迫下(50-70 μmol/L)"微山湖"和"一枝笔"对Ca和Mn的吸收明显下降;Cd胁迫对Fe在叶片的含量影响不明显;同时发现,在50 μmol/L Cd处理下,Cu²⁺在叶片的积累明显增加。由此可见,杞柳2个品种间对镉的吸收和积累差异主要体现在根系,地上部对镉毒害的响应差异不大。;Willows (<em>Salix </em>spp.) are suitable for heavy metal phytoextraction due to their high element accumulation, high metal transport from roots to the shoots and high biomass production. Many species and hybrids of Salix spp. are known to colonise contaminated soils. For example, <em>S. alba</em>, <em>S. viminalis</em>,<em> S. cinerea</em> and <em>S. caprea</em> naturally invade polluted dredged sediment disposal sites. Therefore, there is an opportunity for genotype selection by checking survival, regeneration, and potentially also by testing metals accumulating in tissues which could then be harvested with remediating contaminated soils. Willow species and clones have different tolerance to particular metals, and significant differences were found for the uptake and accumulation of metals among willow varieties and clones. Soil contamination by cadmium due to human and natural activities is one of the most serious environmental problems in the world. The aim of this study is to investigate the cadmium uptake potential of two cultivated varieties (‘Weishanhu’ and ‘Yizhibi’) of <em>Salix integra</em>, of which the variety ‘Yizhibi’ has stronger tolerance to cadmium stress than ‘Weishanhu’ according to previous studies, and to discuss the possible mechanisms which involved in root adaptation under hydroponically cadmium treatment.<br>The results showed the highest content of cadmium was observed in root tissues for both varieties of <em>S. integra,</em> and the cadmium content in phloem tissues was lower than that in roots. The cadmium content in leaves showed the lowest level among roots, phloem and xylem. The cadmium content in the aboveground (including phloem, xylem and leaf) tissues of two varieties of <em>S.integra</em> increased significantly compared to the control with the increase of cadmium treatment in the range of 10-70 μmol/L, and it came to the highest cadmium accumulation at the concentration of 70 μmol/L cadmium, while when exposed to 90 μmol/L cadmium solution, the cadmium content declined in the aboveground parts. The same accumulation patterns were found in roots for two varieties of <em>S. integra</em> in the range of 10-70 μmol/L cadmium treatment. However, when the roots were exposed to 90 μmol/L cadmium treatment, the cadmium content in ‘Weishanhu’ declined sharply, but still rose for that in ‘Yizhibi’. This suggests the roots of ‘Yizhibi’ have greater potentential in uptake of cadmium than the variety ‘Weishanhu’ when exposed to higher concentration of cadmium. <br>The higher uptake and accumulate potential of ‘Yizhibi’ depends on the relatively unchangeable root morphology and fractal dimension under cadmium stress. Comparing to the root images of ‘Weishanhu’ and ‘Yizhibi’ under cadmium treatment, we found the total length, total surface area and volume of roots of ‘Yizhibi’ changed a little compared to the control, while that of ‘Weishanhu’ decreased under cadmium treatment. The fractal dimension of two varieties of <em>S. integra</em> had minor decline, which may suggest both ‘Weishanhu’ and ‘Yizhibi’ prefer to simple root configuration under cadmium treatment. We also found the nutrient uptake in leaves of two varieties of <em>S. integra</em> changed in different cadmium concentration. The Ca and Mn content in leaves decreased significantly in the concentration of 50 and 70 μmol/L cadmium, and no obvious change was observed for Fe content in leaves. It is interesting that the Cu content in leaves of ‘Weishanhu’ increased significantly in the concentration of 50 μmol/L cadmium.