Effects Of Biochar On Degradation Of Lindane And Microbial Communities In Soil

The gain and loss of water in natural environment promote the "dry-wet" cycle of soil,and the "dry-wet" state not only affects the adsorption of soil particles,but also leads to the change of soil redox potential,thus affecting the migration and transformation of organic pollutants in soil.After plant residues fall into the soil,under the condition of "dry-wet" cycle,the residual organic matter might become a part of soil organic matter after physical,chemical and microbial action.Fatty acids are an important part of bio-membrane structure.In this paper,blood powder,corn straw biochar(BC400,BC600)and acid washed biochar(WBC400,WBC600)were added to the soil polluted by lindane.Under the condition of "dry-wet" cycle,biochar(BC)on the degradation of lindane were explored by analyzing the degradation of lindane in soil,the changes of fatty acid composition and saturation in soil,and the changes of soil microbial community.Additionally,the changes of total organic matter and total fatty acids in sterilized soil and non-sterilized soil were measured to explore the contribution of total fatty acids accumulation to the formation of soil organic matter.The results showed that:1)The degradation kinetics of lindane in soil showed that the influence of BC on the degradation of lindane was BC400 > BC600 > WBC600 > WBC400.The adsorption of BC was the main factor to inhibit the degradation of lindane in soil.In addition,the nutrients released by BC promoted the degradation of lindane,and the degradation of lindane in BC added soil was first stimulated and then inhibited.After 89 days of aging in the "dry-wet" cycle soil,scanning electron microscopy(SEM)showed that BC showed aging phenomenon,which appeared collapse and fragmentation of structure,and acid pickling promoted the aging of BC.The structure collapse caused by aging may lead to the desorption of lindane on BC and return to the soil.2)The changes of BC and fatty acid saturation in soil indicated that BC was toxic to degrading microorganisms.The fatty acid saturation of BC added soil was higher than that of the control group,which indicated that BC addition reduced the fluidity of cell membrane,that is,the degradation microbial activity.In particular,acid washing promoted the release of toxic substances and produced microbial toxicity in 400 ℃biochar,while aging caused the surface covering on fresh BC,prevented the release of harmful substances and reduced the biological toxicity.The results showed that the microbial toxicity of 1% and 5% WBC400 reduced the degradation of lindane by 17.6%and 47.2% respectively.The changes of fatty acid saturation(SFA / UFA)showed that the microbial toxicity of BC was 5% WBC400 > 5% BC400 > 5% BC600 > 5%WBC600.3)The addition of BC and blood powder changed the community structure of soil microorganisms.The relative abundance of species at PCo A and genus level showed that fresh BC could significantly change the soil bacterial community structure at the initial stage,and the effect gradually weakened with the time.At the end of culture,the soil bacterial community structure of the control and BC groups were similar,but the effect on eukaryotic community structure was small;the effect of blood power addition on soil bacterial community structure and eukaryote community structure changes was obvious with time.Fresh BC can significantly improve the species richness and diversity of soil bacterial community and eukaryote community,and form a number of dominant degradation populations,including Sphingomonas,flavisolibacter,Azoarcus,parasegetibacter and so on.In addition,the degradation of lindane was accomplished by Sphingomonas,flaviolibacter,parasegetibacter,Azoarcus,bacillus and anaerolinea in the alternating “aerobic-anaerobic”environment.4)Phospholipid fatty acids did not degrade rapidly and completely after microbial death,but some of them remained in soil.Total fatty acids and total organic matter in soil decreased with time,and their trend were basically the same,indicating that fatty acids are an important part of soil organic matter.