【作者】 王璐；

【导师】 刘杏梅； Philip C. Brookes；

【作者基本信息】 浙江大学 ， 土壤学， 2021， 博士

【摘要】 我国耕地镉（Cadmium,Cd）污染状况不容乐观,土壤Cd污染的防治与修复工作亟待加强。近年来,利用生物质炭与生物修复手段相结合进行土壤Cd污染修复因其成本低、效率高、无二次污染等诸多优势得到了广泛的关注。其中,利用生物质炭与Cd抗性细菌制备的复合材料对Cd具有良好的吸附性能,在Cd的水体与土壤修复中展现了不俗的潜力。然而,已有研究仍旧停留在单一的水溶液吸附或土壤Cd的修复效果方面,其机理尚不明晰。目前仍未有关于生物质炭-细菌复合材料运用于稻田Cd修复的相关研究,此外,在施用土壤后,外源微生物、生物质炭和土壤原生微生物群落之间的相互作用知之甚少。因此,本研究拟以一种Cd抗性细菌及两种不同生物质炭为原料,制备生物质炭-细菌复合材料,通过吸附实验及表征,探究其在水溶液中的修复机理及效果;通过土培实验,对其施加入土壤之后各组分之间的相互作用展开研究,明晰其对污染土壤Cd有效性的调控机制及对原生土壤微生物群落的影响;通过水稻盆栽实验,了解其对水稻各生育期的根际土壤Cd形态转化及水稻Cd积累的影响。主要研究结果如下:（1）以Bacillus sp.K1与磁性秸秆生物质炭作为原料制备的磁性生物质炭-细菌复合材料（MBB）吸附水溶液Cd（II）与降低土壤有效态Cd效果最好。在10mg kg^-1的Cd（II）溶液中可去除87.19%的Cd（II）,并可在短期内降低1.6 mg kg^-1Cd污染土壤中90.32%有效Cd。对其进行形貌表征发现,该材料内部以生物质炭作为骨架,负载的Fe₃O₄与细菌分布于生物质炭的表面及孔隙中,外部以交联化的海藻酸钠为膜。（2）水溶液吸附实验结果表明,MBB可有效吸附水溶液中的Cd（II）。MBB对Cd（II）的最大吸附容量为21.50 mg g^-1,与磁性生物质炭相比去除能力提高了230%。MBB通过表面官能团的离子交换和沉淀作用对Cd的吸附,Bacillus sp.K1提供了-NH₂和-OH等新的生物吸附位点,从而显著提高了Cd（II）的去除能力,此外,Fe₃O₄表面形成的羟基络合物也是MBB提高Cd（II）吸附能力的重要因素。（3）土培实验结果表明,MBB在湿润（好氧）和淹水（厌氧）土壤条件下都可有效降低土壤Cd有效性,改变土壤Cd形态。湿润条件下,MBB和SBB（秸秆生物质炭-细菌复合材料）对土壤中Cd的固定与生物质炭的碱性性质和添加细菌的生物吸附作用有关。在淹水条件下,MBB更能降低土壤有效态Cd含量,MBB处理在淹水状态可形成更多的次生铁氧化物,其与Cd的结合可以将土壤酸提取态Cd转化为残渣态。湿润条件下,p H是影响微生物群落（尤其是Bacillus）的最关键因素,SBB处理土壤p H值最高,其Bacillus sp.K1的相对丰度也增加最大。在淹水条件下,微生物量碳的含量与土壤微生物群落的变化相关性最大。MBB增加了土壤微生物量碳的含量,增加了接种细菌Bacillus sp.K1在土壤中相对丰度,改变了土壤微生物群落结构。然而,利用生物质炭接种外源微生物提高了其在土壤中的相对丰度,也增加了土壤中微生物的数量,但由于本地微生物与接种菌株之间的竞争,短期内对土壤微生物多样性产生不利影响,MBB与SBB的添加均降低了土壤微生物的α-多样性。（4）盆栽实验结果表明,1%的MBB可显著提高根际土壤p H,并能短时间提高根际土壤的DOC,并可促使根际土壤中酸提取态Cd更多的转化为残渣态Cd,间接降低Cd转移到水稻的风险。在1%MBB处理中Bacillus属的丰度相比于对照提高了156.57%,这可能是Bacillus sp.K1在土壤定殖所导致的。此外,在水稻成熟期,细菌单独接种的处理有效态Cd与酸提取态Cd含量相比对照已无明显差别。MBB的添加略微增加水稻生物量与籽粒的重量,有效地减少了水稻各器官,尤其是籽粒中Cd的积累,且MBB根表铁膜中Fe的含量显著增加,Cd含量略微下降。本论文的研究表明:制备磁性生物质炭-细菌复合材料可极大的提高生物质炭材料本身的吸附能力。并在淹水条件下展现出最优异的土壤Cd污染修复能力,该复合材料还能降低水稻中的Cd积累,具体作用包括:改善营养状况促进水稻生长;改善根际环境,增强根际中Cd的固定,降低Cd的移动性与生物有效性;促进根表铁膜的形成,阻控根系对Cd吸收。微生物与生物质炭协同可有效的将Cd原位固定,该方式可为农业废弃物的利用、土壤重金属污染修复提供一个新的思路。更多还原

【Abstract】 The Cadmium（Cd）contamination of farmland in China becomes a permanent problem,which has adverse effects on the food quality and safety.Therefore,it is an urgence to remediate the Cd pollution in soil.In recent years,combination of biochar and bioremediation method for Cd remediation attracted extensive attentions,due to its advantages such as low cost,high efficiency and no secondary pollution.Among various materials,the composite prepared by biochar and Cd-resistant bacteria showed a great potential in the remediation of Cd in aqueous solution and soil.However,previous studies just focused on the remediation effects of the materials on Cd remediation in soil or aqueous solution.The remediation mechanisms are still not clear.No research focuses on Cd remediation effects and mechanisms of bacterial-biochar composite during rice plantting yet.Furthermore,the interactions between inoculated microbes,biochar and indigenous microorganism in soil are poorly understood.Therefore,a Cd-resistant bacteria strain and two kinds of biochar were chosen as raw materials to synthesize bacterial-biochar composite.The aims of the study are to 1)determine the mechanism and effect on Cd remediation in aqueous solution and soil;2)explore the interaction between inoculated microbes,biochar and indigenous microorganism and 3)explain the effects of the composite on the rizhospere soil,growth and Cd accumulation of rice.The study may provide theoretical basis and technical support of utilization of bacterial-biochar composite for Cd remediation in paddy soil.The main results are as follows:（1）Magnetic bacterial-biochar composite（MBB）prepared by Bacillus sp.K1 and magnetic biochar had the best effects on Cd adsorption in aqueous solution and available Cd reduction in soil.It could remove 87.19%of Cd（II）in a 10 mg kg^-1 Cd（II）solution and decreased 90.32%of available Cd in soil with a total Cd concentration of1.6 mg kg^-1.Morphology characterization indicated that the biochar was the skeleton inside,with Fe₃O₄ and bacteria distributed on the surface and pore structures.The sodium alginate formed the layer outside.（2）The results of batch experiments showed that MBB could effectively adsorb Cd（II）in aqueous solution.The maximum adsorption capacity of MBB for Cd（II）was21.50 mg g^-1,which was 230%higher than that of magnetic biochar.MBB adsorbed Cd through precipitation and ion exchange with the surface functional groups.Bacillus sp.K1 provided new biosorption sites such as-NH₂ and-OH on the surface of the composite,thus significantly improves the removal capability of Cd（II）.In addition,hydroxyl complexation on Fe₃O₄ surface was also important for Cd（II）adsorption by MBB.（3）The soil incubation experiment indicated that MBB could effectively reduce the available Cd in soil and alter the fraction Cd in both moist（aerobic）and flooding（anaerobic）conditions.Under aerobic conditions,the effect of Cd remediation in soil by MBB and SBB（straw bacterial-biochar composite）was related to the alkaline properties of the biochars and the biosorption of inoculated bacteria.In the anaerobic condition,MBB was more efficient in soil Cd remeidition.More secondary iron oxides could be formed in MBB treatment,which bound Cd in a stable fraction.The p H was the most crucial factor associated with the disruption changes in the microbial community（especially Bacillus）under aerobic condition.SBB increased the soil p H most,and the relative abundance of Bacillus sp.K1 was also the highest in SBB treatment.Under anaerobic conditions,the correlation coefficient between microbial biomass carbon content and soil microbial community is the highest.MBB increased the soil biomass carbon and the survival and colonization of inoculated bacterium,which significantly changed the structure of soil microbial community.However,the inoculation of exogenic microorganisms with biochar applications may have adverse effect on microbial diversity due to the competition between indigenous microbes and inoculated bacterial strains.（4）1%MBB addtion could significantly increased the p H of rhizosphere soil and improved the DOC for a short time.The acid extracted Cd in rhizosphere soil was converted to residual Cd with MBB treatment,which was related to the formation of second iron oxides under anaerobic conditions.The changes could indirectly reduce the risk of Cd transfer to rice.At the maturation stage,the available Cd and acid-extracted Cd concertration of bacterial inoculation（B）treatment were similar with the control.Under MBB treatment,Bacillus sp.K1 may colonize well in soil,and the abundance of Bacillus was increased by 156.57%compared with the control.MBB slightly increased the biomass and grain weight of rice,and effectively decrease the Cd contents in rice,especially in grains.The content of Fe in the root iron plaque of MBB treatment was significantly increased,while the content of Cd was slightly decreased.The results indicated that the MBB can greatly improve the adsorption capacity of the raw biochar.MBB also reduced the accumulation of Cd in rice.The effects of MBB on rice were 1)Improving nutritional status and promoting rice growth;2)Changing the rhizosphere environment and decrease the Cd mobility and avaliability in the rhizosphere;3)Promoting the formation of root iron plaque and inhibiting the accumulation of Cd by rice roots.The combination of biochar and microorganisms can effectively immobilize Cd in situ,providing a new sight for the utilization of agricultural waste and the remediation of soil heavy metal pollution.更多还原