水溶性有机碳对玉米根部Cu吸收过程的影响

采用水培试验方法，将玉米根部环境设定一系列不同的Cu和水溶性有机物(Dissolved organic matter，DOM)浓度条件，研究Cu在玉米根部的吸附和在玉米植株中的积累变化，同时以水和MSCh二级提取方法探讨Cu在玉米根部的结合状态。结果表明，附着在玉米根表与根际分泌物结合的Cu很容易受水相DOM存在的影响。与根部吸附位结合的Cu则不易被水相DOM竞争。植物根对Cu的富集浓度超过茎叶，两部分富集量均随暴露溶液Cu浓度的增加而增加，但茎叶中Cu的富集量与暴露Cu浓度呈非线性相关。根内富集Cu与根表吸附位结合Cu呈现良好的对数线性相关。在相同Cu暴露浓度条件下，DOM对植物组织中富集Cu量影响更加不显著。试验发现作为一种有机配位体，DOM暴露浓度较高时对Cu由根表吸附位进入玉米内部这一过程有负作用。

Influence of Dissolved Organic Matter (DOM) on the Process of Adsorbing and Assimilating Copper by Roots of Maize

Maize's roots were exposed to different concentrations of copper and DOM in nutrient solutions to simulate diverse soil solutions. The adsorptive form of Cu at the root epidermis and the assimilated form of Cu in the root were observed. Meanwhile, a two- step extraction method, which successively extracted the roots with two solutions: water and MgCl2 solution, was employed to study the variation of the speciation distribution of copper at the root epidermis. The results indicated that: the copper combined with the root exudates, which was most common at the root epidermis, was obviously influenced by the concentration of DOM in culture- solution. DOM, however, did not significantly affect the process of surface complexation, which Cu combined at active sites on the roots' epidermis. The accumulation of Cu was higher in root than in shoot, and the concentration of Cu in both two parts increased with the increase of the exposure level of Cu, but the latter (Cu in shoot) appeared no linear relationship with the exposure concentration of Cu .The variation of Cu content in root seemed to not be controlled by the variation of DOM in low exposure concentration. DOM, as an organic ligand, influenced the partition of Cu between the root epidermis and root, and restrained the internalization process of Cu at high exposure level of DOM.