Complexation is a main mechanism controlling the reactions between soil organic matter (SOM) and heavy metals, which still have not been fully understood up to date. The objective of this study was to compare the SOM composition of nonrhizosphere and rhizosphere in low Cr treatment with that in high Cr treatment and to find out how metal concentrations affect the complexation with SOM. The results revealed that both the hydroxyl and the carboxyl were significantly different under different Cr treatment groups. For nonrhizosphere samples, the high Cr treatment tended to have less hydroxyl contents and more structural changes on hydroxyl (3389–3381 cm⁻¹) than the low Cr treatment (3389–3388 cm⁻¹), while in the rhizosphere samples the reverse happened. The gap of the different Cr treated band area in the rhizosphere samples (44 a.u of the gap) was greatly smaller than that in the nonrhizosphere samples (576 a.u of the gap). In both the rhizosphere and nonrhizosphere samples, the high Cr treatment showed greater structural changes on carboxylic acids (11, 12 a.u changes based on the control) than the low Cr treatment (4, 6 a.u). The unsaturated carboxylic acids could account for downward frequency shift and the contents in the nonrhizosphere samples were slightly greater than that in the rhizosphere samples. This study used elemental analysis combined with FTIR spectroscopy to explore the effects of metal concentrations on the complexation of Cr with SOM and the composition of SOM. These findings give a way to understanding part of the complexation mechanisms between the metal and SOM.

络合作用是控制土壤有机物（SOM）与重金属之间反应的主要机制，至今仍未完全了解。这项研究的目的是比较低Cr处理和高Cr处理的非根际和根际的SOM组成，并找出金属浓度如何影响与SOM的络合。结果表明，在不同的Cr处理组下，羟基和羧基均存在显着差异。对于非根际样品，与低Cr处理（3389–3388 cm ^-1）相比，高Cr处理往往具有更少的羟基含量和更多的羟基结构变化（3389–3381 cm ^-1）），而在根际样品中则相反。根际样品中不同Cr处理过的能带区域的间隙（间隙为44 au）比非根际样品的间隙（间隙为576 au）小得多。在根际和非根际样品中，高Cr处理均显示出羧酸的结构变化较大（基于对照，变化为11、12 au），而低Cr处理则显示出较高的结构变化（4、6 au）。不饱和羧酸可引起向下频移，并且非根际样品中的含量略高于根际样品中的含量。这项研究使用元素分析与FTIR光谱相结合，探讨了金属浓度对Cr与SOM的络合以及SOM的组成的影响。