外源稀土作用下根–土界面元素转化、分布及其植物有效性的研究进展

外源稀土（RE）可导致根-土界面物理、化学及生物学特性发生根本性变化，特别是根系主导的根际动态过程的变化。如施用不同剂量RE条件下，稀土元素（REE）与根系的相互作用使根系生长、酶活性、细胞质膜透性等受到不同程度的影响。根系生长、酶活性的变化反映了植物可能通过根系形态学、生理学的适应性和非适应性变化机制来改变根系吸收养分、REE及重金属离子的能力，直接影响根际离子进入根系中的含量；而根系细胞质膜透性的变化则反映了植物可能通过根系分泌作用的适应性和非适应性变化机制来改变根系有机酸、质子等的分泌状况，使之作用于根际环境，制约养分、REE及重金属元素在根际的形态转化与迁移分布模式，从而间接影响根际离子进入根系中的含量。本文从外源RE对根系生长状况和酶活性的影响；对根系细胞质膜透性和分泌作用的影响；对根际养分、REE及重金属元素动态的影响；对根系养分、REE及重金属元素吸收分布的影响等4个方面的国内外文献出发，就土壤-植物系统中外源RE作用下根-土界面养分、REE及重金属元素的转化、分布及其植物有效性的响应变化与相关机制做出综述，同时提出目前研究中存在的问题，对今后的研究方向进行展望。

Effects of exogenous rare earths (REs) on transformation and distribution of elements at the root-soil interface and their phytoavailability: a review

Exogenous rare earths (REs) application could alter the physical, chemical and biological characteristics at the root-soil interface, especially root-induced changes in the rhizosphere of plants. For example, exogenous REs, induce the extent of changes in root growth, root enzyme activities and root cell membrane permeability. Root biomass, some relative root enzyme activities and root activity reflect the capacity for absorption of nutrient (N, P, K, Ca, etc) and REE (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, etc) and heavy metal (Fe, Mn, Cu, Zn, Pb, Cd, Cr, Ni, etc) ions from rhizosphere soil solution. Hence, the morphological and physiological changes of root system result in the changes in uptake of rhizosphere nutrient and metal ions into plant roots directly. On the other hand, the release status of root exudates (organic acid, hydrogen ions, etc) affected by the change in root cell membrane permeability reflects the influence of rhizosphere environment on the transformation and distribution behaviors of nutrients and metals in the rhizosphere of plants. Such release could also further induce changes in uptake of rhizosphere nutrient and metal ions into plant roots indirectly. In this paper, the effect of exogenous REs application on root-soil micro-ecosystem and its environmental and biological effects in soil-plant systems were elucidated from four aspects as follows: 1) exogenous REs application impacts on root growth and root enzyme activities; 2) exogenous REs application impacts on root cell membrane permeability and root exudation; 3) exogenous REs application impacts on rhizosphere pH and the transformation and distribution (accumulation or depletion) of nutrients and metals in the rhizosphere of plants; 4) exogenous REs application impacts on the uptake and distribution of nutrients and metals by the roots of plants. Furthermore, some possible explanations for the above mentioned aspects were provided respectively, among which more attention was paid to the fractionation mechanisms of REEs at the root-soil interface because of their significance to studies on the phytoavailability of REEs.