小球藻对土壤-水稻系统砷化学形态转化的影响

为揭示绿藻对土壤-水稻系统砷形态转化的影响特征，系统分析了不同浓度小球藻共存条件下水稻土砷氧化还原与溶解释放行为的变化，并结合水稻培育试验，对小球藻影响水稻砷吸收与体内砷形态的发生机制进行探讨.试验设置对照组及小球藻浓度（以体积分数计）分别为1%、5%、10%的处理，研究了小球藻对溶液体系、淹水土壤体系和淹水土壤-水稻体系中砷的化学形态转化的作用.结果表明:加藻组使As（Ⅲ）溶液和淹水土壤E_h（氧化还原电位）与pH均普遍高于对照组.在As（Ⅲ）溶液体系中，加藻组As（Ⅲ）氧化转化率较对照组升高2.38%~4.95%，该作用在淹水土壤中得到印证，小球藻的共存使土壤孔隙水ρ[As（Ⅴ）]较对照组升高129.22%~221.41%，而ρ（甲基砷）出现显著下降（5.25%~53.31%）.水稻栽培试验进一步发现，小球藻明显促进土壤中晶体态铁铝氧化物向弱结晶与无定形铁铝氧化物结合态砷等的转化，导致水稻幼苗对砷的吸收积累量增加-3.4%~23.11%，推测这与小球藻作用下土壤孔隙水ρ（DOC）的增加密切相关.研究显示，尽管小球藻有利于提高淹水土壤体系E_h并加速As（Ⅲ）的氧化转化，但小球藻可能通过有机酸等分泌物的竞争吸附作用促进铁铝氧化物结合态砷的溶解释放，从而增加水稻砷吸收；淡水藻类对土壤-水稻体系砷吸收积累的风险值得引起高度关注，并需要在大田试验中进一步加以验证. 

Effects of Chlorella vulgaris on Transformation of As Chemical Speciation in Soil-Rice Paddy System

To reveal the influence of green algae on the speciation transformation of As in soil-rice paddy systems, the important changes in As redox and dissolution release behavior in paddy soil were studied under conditions of different concentrations of Chlorella vulgaris. Based on a paddy cultivation experiment, the mechanism whereby C. vulgaris affects the absorption and transformation of As was discussed. A control group and groups with C. vulgaris set at 1%, 5% and 10% were established. The effects of C. vulgaris on the chemical transformation of arsenic in a solution system, flooded soil system and flooded soil-rice system were studied. The results showed that with the treatment of C. vulgaris the oxidation-reduction potential (E_h) and pH in As(Ⅲ) solution and flooded soil were generally higher than in the control. In the As(Ⅲ) solution system, C. vulgaris treatment increased the As(Ⅲ) oxidation conversion rate by 2.38%-4.95%. This effect was confirmed in the flooded soil. The coexistence of C. vulgaris caused the concentration of As(Ⅴ) in soil porewater to increase by 129.22%-221.41% compared with the control, while the methyl arsenic concentration decreased significantly (5.25%-53.31%). In the paddy cultivation experiment, it was further found that C. vulgaris accelerated the transformation of As species to unstable ones, such as crystalline iron oxide-bond As to weakly crystalline and amorphous iron oxide-bond As in the soil, resulting in an increase in the absorption and accumulation of As in rice seedlings by from -3.4% to 23.11%. It is speculated that this process is closely related to the increase of in the DOC content of porewater under the action of C. vulgaris. According to the results of this study, C. vulgaris helps to increase the E_h of the flooded soil system and accelerate the oxidation of As(Ⅲ), but C. vulgaris may also promote the dissolution and release of iron oxide-bound As due to the competitive adsorption of organic acids and other secretions, thereby increasing rice As absorption. The results highlighted that the effects of freshwater algae on the risk of assimilation and accumulation of As in soil-rice systems deserve high attention and need to be further verified in field experiments.