不同来源可溶性有机质对稻田土壤中砷甲基化的影响

Effect of dissolved organic matter from different sources on arsenic methylation in paddy soils

以湖南省石门县雄黄矿区砷污染水稻土为试验用土,采用离心管培养试验探究了由猪粪、牛粪、鸡粪和水稻秸秆制备的4种可溶性有机质(DOM)对土壤中砷甲基化的影响。结果表明:添加不同有机碳(TOC)浓度的DOM可显著改变水稻土壤中砷的形态,且不同处理中各形态砷含量均随TOC浓度增加呈现不同程度的增加。当土壤溶液TOC浓度为320 mg·L^-1时,4种DOM处理的土壤溶液中甲基态砷含量分别占总砷的75.8%(猪粪DOM)、75.7%(牛粪DOM)、68.3%(鸡粪DOM)和61.8%(水稻秸秆DOM);土壤溶液中甲基态砷含量与TOC浓度呈现显著正相关关系(P<0.01),表明TOC浓度增加可显著促进土壤中砷的甲基化。各处理对土壤砷甲基化的激发作用大小排序为猪粪DOM(0.0161μg·L^-1)>鸡粪DOM(0.0147μg·L^-1)>牛粪DOM(0.0099μg·L^-1)>水稻秸秆DOM(0.0082μg·L^-1);添加320 mg·L^-1 TOC浓度的DOM处理中土壤砷甲基化功能基因arsM拷贝数均高于对照(添加等体积超纯水),其中猪粪处理最高,为3.36×109 copies·g^-1,约是对照的2倍;不同DOM作用下土壤pH变化规律为水稻秸秆>牛粪>鸡粪>猪粪,土壤EC值变化规律为水稻秸秆>鸡粪>牛粪>猪粪。综上,不同来源的DOM可差异性地影响水稻土壤中砷甲基化效率,通过合理施用有机肥有望减少土壤中砷的甲基化,从而在一定程度上减轻水稻直穗病发生。

Culture experiment using centrifuge tubes loaded with arsenic(As)-contaminated paddy soils from realgar mining area of Shi⁃men County of Hunan Province was conducted to study the effect of dissolved organic matter(DOM)from different sources,such as from pig manure,cow dung,chicken manure,and rice straw,on arsenic methylation in paddy soils.The results indicated that DOM addition sig⁃nificantly changed the species of As in paddy soil,and the content of each As species increased under varying degrees with total organic carbon(TOC)concentrations.When the TOC reached 320 mg·L^-1 in soil solution,the content of methyl-As under the four treatments of DOM were 75.8%,75.7%,68.3%,and 61.8%of the total As content,respectively.A significantly positive correlation(P<0.01)between methyl-As contents and TOC concentration in soil solution was found.The As methylation in paddy soil was evidently accelerated after the addition of DOM.As methylation efficiency from high to low was in the order of pig manure DOM(0.0161μg·L^-1),chicken manure DOM(0.0147μg·L^-1),cow dung DOM(0.0099μg·L^-1),and rice straw DOM(0.0082μg·L^-1).When the TOC applied reached 320 mg·L^-1 in the soil solution,the copy numbers of arsM in soil with DOM addition were all higher than these in control,and the highest number was found in pig manure DOM treatment with 3.36×10^9 copies·g^-1 which was about 2.0 times higher than that in the control.The soil pH after addition of different DOM was from high to low in the order of rice straw,cow dung,chicken manure,and pig manure.The pH values in⁃creased with increase in TOC concentration.The soil electrical conductivity(EC)varied from high to low in the order of rice straw,chicken manure,cow dung,and pig manure.In conclusion,DOM from different sources can differentially affect As methylation efficiency in paddy soils.It is expected that reasonable application of organic fertilizer might reduce the occurrence of rice straighthead disease to some extent by reducing the content of methyl-As in paddy soils.