不同pH条件下腐植酸对土壤中砷形态转化的影响

Effects of humic acid on transformation of soil As in different pH conditions

为了探索在不同pH条件下腐植酸对土壤中砷形态转化及生物毒性的影响,应用油菜盆栽试验,检测砷加入土壤后15 d、45 d、90 d土壤中AE-As(水溶态、可交换态和碳酸盐结合态)Fe,Mn-As(铁/锰氧化物结合态),O,S-As(有机物及硫化物结合态),Res-As(残渣态)的含量及油菜生物量。结果表明,外源水溶态砷加入土壤后均迅速向相对稳定的形态转化,15 d时A3H1(pH 9.5,腐殖酸用量为0 g/kg)和A3H4(pH 9.5,腐殖酸用量20 g/kg)处理的AE-As含量分别为13.40 mg/kg、9.23 mg/kg,转化率分别为78.7%、82.51%;在90 d时,A3H4处理的AE-As、Fe,Mn-As含量分别为6.28 mg/kg、1.23 mg/kg,仅为处理A3H1处理的53.9%和10.7%,O,S-As、Res-As含量分别为20.24 mg/kg、41.21 mg/kg,是处理A3H1的165%和127%。说明腐植酸更有利于土壤中AE-As向其他相对稳定的形态转化,主要体现在O,S-As的增加,腐植酸对碱性土壤中砷向较稳定形态转化的促进作用更加显著,而且与腐植酸的施用量呈正相关。外源砷在碱性条件下对植物的毒害更大,腐植酸用量在10 g/kg土时就可以有效降低砷的毒害。

Rape cultivated in pot was used to investigate the effects of humic acid on the form transformation and biotoxicity of As in soils.The contents of AE-As,Fe,Mn-As,O,S-As and Res-As in soils and the rape biomass were measured on the 15th,45th and 90th day.The result shows that the exogenous hydrosoluble As is rapidly transformed to a relatively stable form in soils.After 15 days,the AE-As contents of A3H1（pH 9.5,humic acid rate is 0 g/kg） and A3H4（pH 9.5,humic acid rate is 20 g/kg） are 13.40 and 9.23 mg/kg respectively,the conversion rates reach up to 78.7% and 82.51%.On the 90th day,the contents of AE-As and Fe,Mn-As of A3H4 are 6.28 and 1.23 mg/kg,respectively.Which account for only 53.9% and 10.7% of A3H1.The contents of O,S-As and Res-As are 20.24 and 41.21 mg/kg,which are 165% and 127% of A3H1.These results suggest that humic acid facilitates the AE-As transform into other stable forms,and the most obvious change is the increase of O,S-As.Humic acid demonstrates a more significant promotive effect when the soil is alkaline,which is positively correlated with the humic acid consumption.The exogenous As has a stronger toxicity to plants in alkaline conditions.The dosage of humic acid at 10 g/kg soil is effective to decrease the As toxicity.