Effects Of Biochar Amendment On The VOC Emission From And The Microbial Diversity In Straw-amended Soils

Straw is widely ruturn into soils in our country,and release a lot of volatile organic pollutants?VOCs?during their decomposition.VOCs can not only produce tropospheric ozone?O3?and secondary organic aerosol?SOA?,but also deplete the stratospheric ozone-layer and thus influence global radiation budget and global climate.So it is necessary to seek a way to reduce VOCs emissions from straw-amended soils.Biochar amendment can inhibit the greenhouse gas?CO₂,CH4 and N2O?emission from soil because of its structural characteristics,but its effect on VOC emissions from straw-amended soils is still unknown.In addition,straws returned are decomposed by soil microorganisms,which can be affected by biochar amendment.Therefore,it is better to explore the influence of biochar amendment on VOCs emission through studing on the changes of microbial community structure and diversity by biochar amendment.In the present study,a laboratory study was conducted systematicly to investigate the emission of VOCs,the number of culturable microorganisms,microbial biomass carbon and bacterial community structure and diversity during the whole experiment in straw-amended soils without?SW?and with?SBW?biochar.The results provided the information to explore the effects of biochar amendment on VOCs emission during straw return.The main results were as the following:?1?VOCs released from straw-amended soils were mainly composed of non-methane hydrocarbon compounds?NMHCs?,volatile sulfur compounds?VSCs?and oxygenated volatile organic compounds?OVOCs?.Biochar amendment resulted in the obvious increase of VOC?especially OVOC?emissions,but the significant decrease of VSC emissions.The emissions of total VOCs were 7.29 mg kg-1 and 36.5 mg kg-1 in SW and SBW treatment,respectively,among which OVOCs?includes ketones,alcohols,aldehydes and esters?dominated and shared 95.3% and 99.1% of total VOCs emitted.The emissions of total C2-C5 NMHCs?composed of 5 alkanes and 5 alkenes?were 211 ?g kg-1 and 257 ?g kg-1 in SW and SBW treatment,respectively,while those of VSCs?included DMS,DMDS,DMTS and CS2?were 132 ?g kg-1 and 81.4 ?g kg-1 in SW and SBW treatments,respectively.For individual VOCs,in SW treatments acetone was the primary emitted VOCs and contributed to 45.3% of total VOCs,followed by ethanol,2-butanone,2-pentanone,i-propanol,2-butanol and acetaldehyde,and the top seven VOCs shared 91.7% of total VOCs.In SBW treatment,acetone was also the primary emitted VOCs and contributed to 38.3% of total VOCs.It was followed by 2-pentanone,2-butanone,ethanol,i-propanol,2-hexanone and 2-heptanone,and the top seven VOCs contributed to 95.9% of total VOCs.?2?The emission rates of VOCs varied obviously with incubation time during the process of straw return into soil in both two treatments.In SW treatment,the emission rates of 10 NMHCs varied in their time series during the incubation period,forming one or two peak value at day 0-24 and 24-56,while those of 4 VSCs occurred in the first 30 days and reach a peak value at day 12.Most OVOCs were emitted completely in the first 30 days and reached a peak value at day 20-30.In SBW treatment,the emission rates of 10 NMHCs formed one or two peak value at day 0-17 and 24-56,while those of DMS,DMDS and DMTS reached a peak value at 17 days,and released completely in the first 34 days.The emission rate of CS2 reached one or two peak walue at 4-17 days and 24-44 days,and those of OVOCs reached one or two peak walue at days 0-24 and 34-56.?3?The bacterial DGGE profiles and genetic diversity index revealed that the biochar amendment promoted the change of the DGGE band position and gray value as well as the evenness of bacterial communities,but made no difference?P > 0.05?of the Shannon-Wiener index and richness of the bacterial communities between two treatments.The clustering analysis showed that the composition of the bacterial community in SBW treatment was divided into five categories,while that in the SW treatment was separated into six groups.The analysis of 16 S rRNA gene sequences and the bacterial community structure indicated that biaochar amendment led to the disappearance of Actinobacteria and Nitrospira and the appearance of Spirochaetes,Gemmatimonadetes,Chloroflexi and WS3,as well as a relative increase of Firmicutes and Proteobacteria and reduce of Acidobacteria and Bacteroides.?4?The correlations between VOC fluxes and microbial characteristics?bacterial community,microbial biomass carbon,respiratior rate and population?indicated that microorganisms play an important role in VOCs emission.The correlations between VOC fluxes and chemical elements in soils suggested that the substrate affect VOC emissions from straw-amened soils.