秸秆和Eh对稻田土壤溶解性有机质组成及金属释放的影响

为探究秸秆添加对氧化还原条件变化下稻田土壤重金属释放的影响，本文选取典型重金属污染稻田土壤，通过微宇宙试验结合三维荧光光谱等手段，分析了土壤溶液化学性质、溶解性有机质（DOM）、金属释放之间的动态关系。结果表明：添加秸秆增加了厌氧期Fe、Mn、As、Cd等金属的释放，同时影响了DOM组成。土壤DOM中类蛋白（C3）含量在培养期总体降低（P<0.05）；类腐殖质含量呈现厌氧期上升、好氧期下降的趋势。结构方程模型（SEM）分析显示，Eh的变化与Mn和As的溶出显著负相关（路径系数分别为-0.662和-0.528，P<0.01），同时，Eh还通过影响土壤类腐植酸C2（路径系数-0.816，P<0.01）控制As的释放（路径系数0.244，P<0.05）。因此，稻田土壤干湿交替造成的Eh变化和秸秆还田措施不仅可直接影响重金属的溶出，也可通过DOM含量和组成进一步控制其释放。

Effects of straw addition and Eh on dissolved organic matter composition and metal release in paddy soil

A typical paddy soil that was contaminated with heavy metals was selected to explore the effects of straw addition on the release of metals in the soil under redox change, and the dynamic relations among soil solution chemistry, dissolved organic matter(DOM), and metal release were studied via micro-universe test and three-dimensional fluorescence spectrum analysis method. The results demonstrated that straw addition enhanced Fe, Mn, As, and Cd release at the anaerobic stage, and had a significant effect on DOM composition. The C3 protein content in DOM was significantly decreased during anaerobic to aerobic(P<0.05). The humus-like content increased in the anaerobic stage and then decreased in the aerobic stage. Structural equation model(SEM)analysis showed that Eh change was negatively correlated with the dissolution of Mn and As(path coefficients -0.662 and -0.528, P<0.01). Meanwhile, Eh influenced soil humic acid C2(path coefficient -0.816, P<0.01)to control As release(path coefficient 0.244, P<0.05). Therefore, the change of Eh caused by alternate wetting and drying of both the paddy soil and the straw returning can not only directly affect the dissolution of heavy metals but also control their release through DOM content and composition, which are conducive to further clarification of the mechanism of metal release in farmland soil.