【作者】 徐敏；

【导师】 伍钧；

【作者基本信息】 四川农业大学 ， 生态学， 2020， 博士

【摘要】 磷素流失及重金属污染是土壤退化的主要原因之一。在人口增长与资源流失的压力下,如何减少磷素流失,控制重金属污染,提高农田产出及保障粮食安全是当下亟需解决的问题。近年来,生物炭因具有较好的吸附性能,可降低污染物的生态风险,是一种环保、经济且有效的修复材料,是当前环境领域研究的热点。基于此,本研究以猪粪生物炭(Swinemanure-derivedbiochar,MB)、玉米秸秆生物炭(Maize straw-derivedbiochar,SB)和松木生物炭(Pine-derivedbiochar,PB)为材料,通过批量吸附试验分析生物炭对磷(Phosphorus,P)、砷(Arsenic,As)和铬(Chromium,Cr)的吸附效果、机理、及两两的交互作用;并将生物炭应用于水-土壤-水稻体系,探究生物炭施用对P、As、Cr在该体系分配的影响,以及水稻与微生物对生物炭施用的响应,研究生物炭处理下P、As、Cr在水-土壤-水稻系统中的迁移分配规律及驱动因子,探讨生物炭用于治理P、As、Cr复合污染土壤的可能性,对农田可持续发展及土壤修复意义匪浅。主要的研究结果如下:1)生物炭的性质受热解温度及制备原料的影响。随着热解温度的增加,生物炭pH、灰分含量增加,挥发分、阳离子交换量(Cation exchange capacity,CEC)降低;C含量增加,H、O、N元素降低,极性、芳香性、疏水性增强;官能团减少;孔隙度表现出先增加后降低的趋势;有效K、Zn、Fe含量增加,而有效P、Ca、Mg含量降低。与SB和PB相比,MB具有更高的pH、灰分以及P、K、Cu、Fe、Zn含量;与MB与SB相比,PB孔隙结构更明显,C含量更高。整体而言,CEC受温度影响较大;而pH、灰分、矿质元素组成等受生物炭原料影响较大。2)不同原料生物炭对P、As、Cr的吸附能力分别表现为MB<SB=PB(p<0.05)、MB>SB=PB(p<0.05)、MB>SB>PB(p<0.05)。PB700、MB700、MB500 分别对 P、As、Cr有最大吸附值,分别为5.64mg/g、0.3mg/g、6.57mg/g。MB对P的吸附机理主要为静电吸附及官能团络合;SB与PB对P固定的主要机理为灰分共沉淀及静电吸附;生物炭对As的吸附与矿物及灰分含量密切相关;矿物络合是生物炭固定Cr的主要机理。P、As、Cr之间交互作用:P与As会相互竞争吸附位点,降低二者的吸附;As与Cr以原子比0.6:1络合,增加二者的吸附;而P与Cr之间的竞争关系较小。当三者共存时,与单一系统相比,生物炭对P、As、Cr的吸附量分别提高了 9-83%、71-73%、42-91%,表明采用生物炭处理P、As、Cr复合污染系统具有可行性。3)生物炭施用能显著提高土壤有机质(Soil organic matter,SOM)、全氮(Total nitrogen,TN)、速效磷(Availablephosphorus,AP)、全磷(Totalphosphorus,TP)、速效钾(Availablepotassium,AK)含量,降低碱解氮(Availablenitrogen,AN)含量。不同原料制备的生物炭处理下SOM的含量表现为PB>MB>SB(p<0.05),而N、P、K含量表现为 MB>SB=PB(p<0.05)。相关性分析显示,土壤磷饱和度(DegreeofP saturation,DPS)、CaCl2-Cr含量与结晶态铁含量呈极显著相关关系,表明铁的形态影响P、Cr释放,而CaC12-As与SOM呈显著正相关关系,表明SOM促进As的移动。可见,SOM、铁氧化物在P、As、Cr固持上发挥着重要的作用。4)与对照相比,5%(w/w)的SB处理显著提高了水稻生物量,而5%的PB处理显著降低了生物量,其余各处理差异不显著。生物炭施用降低了叶片丙二醛含量,提高根系还原力。与对照相比,5%的MB处理下根系P含量增加了 43%,根系As含量降低了 93%,表明MB施用对根系P含量的增加可降低对As的吸收。1%和5%的SB处理下茎叶As含量显著降低。5%的PB处理下根系As含量降低了 54%,1%的PB处理下根系Cr含量降低了 97%。茎叶中P、As、Cr含量与Fe呈显著正相关关系,表明几种元素在水稻的转运具有相同的机制。可见,Fe对P、As、Cr在水稻体系的分配具有重要的作用。5)DCB-Fe(二硫代柠檬酸氢钠浸提)与DCB-P、DCB-As、DCB-Cr均呈极显著正相关关系,相关系数分别为0.54、0.66、0.69。孔隙水中Fe含量与孔隙水中As、Cr含量呈极显著正相关关系,相关系数分别为0.86、0.79。可见,生物炭施用可通过影响铁膜(Ironplaque,IP)的形成及Fe的循环来影响水稻对P、As、Cr的吸收及水稻的生长。一方面,铁膜的形成可提高对P、As、Cr在铁膜的储存,降低水稻对三者的吸收。另一方面,Fe的移动性增强可降低对As、Cr固定,增加根系对As、Cr吸收。与对照相比,PB处理降低了铁膜含量,降低了对P、As、Cr的缓冲能力,同时提高孔隙水中Fe含量,导致了 As、Cr的释放及毒性,从而抑制水稻生长。6)与对照相比,MB、SB处理下显著提高了土壤微生物多样性指数(Shannon)及丰度指数(Observed species、Chao1),而PB处理下微生物多样性及丰度指数均降低;在门水平上,生物炭施用提高了放线菌(Actinobacteria)、酸杆菌门(Acidobacteria)、绿弯菌(Chloroflexi)、绿细菌门(Chlorobi)、芽单胞菌门(Gemmatimonadetes)的相对丰度。在属水平上,与对照相比,生物炭施用提高了土壤促生长菌丰度(17-53%);抑制了解磷菌(33-57%)及铁还原菌(34-57%)的生长,表明生物炭的施用可促进水稻生长,抑制P、Fe的循环。孔隙水Fe含量与地杆菌属(Geobacter)丰度及SOM呈极显著正相关关系,可见地杆菌属(Geobacter)主要参与Fe的循环,影响As与Cr的释放,是控制As、Cr土壤修复的关键因子。其中,SOM参与并刺激Fe的循环过程。因此,抑制铁还原菌,特别是地杆菌属(Geobacter)的生长,降低Fe的还原,可有效降低As、Cr的迁移。更多还原

【Abstract】 Phosphorus loss and heavy metal contamination are the major factors causing soil degradation.In this regard,a simultaneous decrease of phosphorus loss and heavy metal bioavailability is emergently required to improve soil productivity and meet future food needs,which is still a thorny issue.Over the past few decades,biochar application is a very popular method to decrease the eco-risk of contaminants due to its excellent absorption capacity.Besides,biochar has been recognized as an eco-friendly,and low-cost material for the removal of contaminants,which is a current research focus.Base on this situation,swine manure derived biochar(MB),maize straw derived biochar(SB),and pine derived biochar(PB)were chosen in this study.A batch adsorption experiment was conducted to explore the absorption characteristic and underlying adsorption mechanisms of phosphorus(P),arsenic(As),and chromium(Cr)to biochar,and the interactive effects among P,As and Cr.Moreover,a pot experiment was conducted to analysis the effects of biochar addition on the distributions of P,As and Cr in the water-soil-rice system,and the response of rice growth and bacterial community structure to demonstrate the P,As and Cr distribution characteristic and the major driver of the contaminants translocation in the system.Hence,Practical implementation of biochar to remediate soil cocontaminated with P,As and Cr has been critically discussed.The results were important to maintain sustainability in agricultural soils and contaminants remediation.The results are as follows:1)Biochar properties were strongly dependent on pyrolysis temperatures and feedstocks.Specifically,the pH values and ash concent significantly increased with increasing temperature,while volatile and cation exchange capacity(CEC)significantly decreased.Moreover,C content was increased whereas H,O,N were reduced with increased pyrolysis temperature;as such,polarity,aromaticity,and hydrophobic of biochar were increased,the number of functional groups was reduced.Furthermore,the porosity of biochar was increased first and then reduced.The availabilities of K,Zn,and Fe were increased,while the availabilities of P,Ca,Mg were reduced with increasing temperature.In addition,compared with SB and PB,MB had higher value of pH,and higher amounts of ash,P,K,Cu,Fe,and Zn.However,PB had more abundant porosity,higher C concent.Overall,CEC was highly variable depending upon the pyrolysis temperature,whereas pH,ash,and mineral compositions were significantly impacted by feedstocks.2)The orders of adsorption capacities of P,As and Cr to different biochar were MB<SB=PB(p<0.05),MB>SB=PB(p<0.05),and MB>SB>PB(p<0.05),respectively.The highest adsorption capacity for P was found in PB700 treatment with adsorption capacity of 5.64 mg/g;while MB700 has the highest adsorption capacity for As with adsorption capacity of 0.3 mg/g,and MB500 has the highest Cr adsorption with the adsorption capacity of 6.57 mg/g.Electrostatic adsorption and functional group complexation were the dominant mechanisms for P absorption to MB,while complexation with ash/mineral,and electrostatic adsorption were the dominant mechanisms for P absorption to SB and PB.Arsenic absorption was closely associated with ash and minerals.Minerals complexation was the dominant mechanism for Cr absorption,electrostatic adsorption contributed a secondary effect for Cr absorption.There were strong interactive effects among P,As and Cr.Specifically,the competitive adsorption between P and As inhibited their adsorptions to biochar.In the binary system,both As and Cr adsorptions were increased due to the formation of As-Cr complex mineral with 0.6:1 atomic ratio of As/Cr.The interactive effect between P and Cr was weak.Compared with single system,P,As and Cr absorption capacities increased by 9-83%,71-73%,42-91%in the multimetal system using biochar,suggesting biochar exhibits a great potential to act as a applicable material for co-present P,As and Cr removal.3)Biochar addition significantly increased soil organic matter(SOM),total nitrogen(TN),available phosphorus(AP),total phosphorus(TP),available potassium(AK)concentrations,while significantly reduced available nitrogen(AN)concentration.The increases of SOM in different biochar treatments ranged in order from PB>MB>SB(p<0.05),while the increases of soil N,P,and K concentrations in different biochar treatments ranged in order from MB>SB=PB(p<0.05).There is no significant difference between Cr fractions under different treatments.Degree of P saturation(DPS)and CaCl2-Cr exhibited significant correlations with crystalline Fe,indicating Fe affected P and Cr release,while CaCl2-As was correlated positively with SOM,suggesting the increase of SOM induced As release.Therefore,SOM and Fe oxides play important roles in P,As and Cr immobilization.4)Compare with control,5%-SB addition significantly increased rice biomass,while 5%-PB addition significantly reduced rice biomass,the trends for rice biomass under the other treatments were not remarkable.Compare with control,biochar addition significantly reduced malondialdehyde concentration and increased root reductive activity.5%-MB addition increased root P by 43%,while reduced root As by 93%,indicating that the increase of P in 5%MB treatment inhibited As uptake.SB addition at dosages of 1%and 5%reduced shoot As concentration.5%-PB addition reduced root As,and 1%-PB addition reduced root Cr by 97%.The significant relationships between shoot P/As/Cr and shoot Fe indicated they might share the same uptake mechanism in rice.The results showed that Fe plays a centrol role in P,As and Cr translation in rice.5)DCB-Fe(dithionite-citrate-bicarbonate extractable Fe)exhibited significantly positive correlations with DCB-P/DCB-As/DCB-Cr,with values of correlation coefficients of 0.54,0.66 and 0.69,respectively.Moreover,pore water Fe exhibited significantly positive correlations with pore water As and Cr concentrations,with values of correlation coefficients of 0.86 and 0.79.The results indicated that biochar addition affected P,As and Cr accumulations in rice tissuse and rice growth through the formation of iron plaque(IP)and Fe cycling.On one hand,iron plaque formation increased P,As and Cr concentrations in iron plaque,decreasing their uptake.On the other hand,the release of Fe reduced the immobilization of As and Cr,and thus increasing their uptake by root.Compared with control,the addition of PB inhibited iron plaque formation and stimulated Fe reduction,subsequently increasing As and Cr release,thus increasing the toxicity of As and Cr,suppressing rice growth.6)Compared with control,MB and SB application significantly increased microbial diversity(Shannon)and richness(Observed species,Chao1)indexes,whereas PB application significantly reduced microbial diversity and richness indexes.At the phylum level,biochar addition significantly increased the relative abundance of Actinobacteria,Acidobacteria,Chloroflexi,Chlorobi,and Gemmatimonadetes.At the genus level,biochar addition significantly increased the relative abundance of plant growth-promoting rhizobacteria(PGPR)by 17-53%,while reduced P-solubilizing bacteria(PSB)and iron-reducing bacteria(IRB)relative abundance by 33-57%and 34-57%,respectively.Pore water Fe exhibited significantly positive correlations with Geobacter and SOM.It suggested that Geobacter was the key factor controlling Fe cycling,influencing As and Cr release.Besides,SOM was participated in and stimulated Fe reduction.Therefore,suppressing IRB growth especially for Geobacter and decreased Fe reduction can be an effective pathway to reduce As and Cr release.更多还原