Effect Of Biochar Addition On Soil Organic Carbon Mineralization And Microbial Community Structure Of A Heavy Metal-Contaminated Paddy Soil

Since the middle of last century,with the rapid development of industrialization in China,the unreasonable application of chemical fertilizers and pesticides,the pollution of heavy metals in paddy soil has become more and more serious,and the effects of heavy metal pollution on the forms of organic carbon in paddy soils are different.It also affected soil microbial biomass and microbial community structure,and then affected soil organic carbon mineralization,thus changing the mineralization and turnover of soil organic carbon.In recent years,more and more attention has been paid to the effects of pyrolysis biochar from agricultural wastes on soil and environment,especially on the remediation of polluted soil.biochar may be affected by direct and indirect effects Soil organic carbon mineralization,soil microbial abundance and community structure change soil biological function and ecosystem recycle.Due to the wide differences in soil properties,biochar species and field test conditions,there is still great uncertainty about soil microbial effects of biochar.Although there have been many experimental reports on the use of biochar in the treatment of heavy metal pollution,there is a lack of research on the effects of biochar addition on organic carbon mineralization and the understanding of the changes in soil microbial abundance,activity and function.This has become a weak field of agricultural biochar science and technology.Therefore,the application of organic carbon in paddy soil in this environment is discussed.It is of great significance to further understand the carbon sequestration and emission reduction effect of paddy soil under pressure.In this study,the effects of biochar and heavy metal pollution on the stability of organic carbon in paddy soil were studied.Corn(C4 crop)straw biochar was added to paddy soil samples with long-term rice cultivation(C3 crops)and long-term heavy metal pollution(from the downwind of the pollution source to different distances)and man-made addition of heavy metals to paddy soil samples.The effect of carbon addition on mineralization of new and old organic carbon in paddy soil polluted by heavy metals was investigated,and the change of activated organic carbon pool component and excitation effect intensity during culture were analyzed.The abundance of bacteria and fungi in soil was analyzed by HiSeq high flux sequencing technique.Sample index and community structure were used to explore the effects of biochar addition on microbial community structure at different levels of heavy metal pollution.It provides the basis of microbial stability for studying the mechanism of organic carbon stability of paddy soil by heavy metal pollution.The main results are as follows:(1)the addition of biochar can significantly promote the mineralization rate of long-term heavy metal contaminated paddy soil and organic carbon contaminated by exogenous heavy metals,and the initial mineralization rate of soil is related to the addition of biochar.The higher the amount of biochar,the faster the mineralization rate of organic carbon.Under the same carbon application level,the respiration rate and cumulative emission of CO2 in unpolluted and low polluted soils were significantly higher than those in high polluted soils.(2)the content of MBC,POC,LOC in the biochar treated soil after 60 days' cultivation was significantly higher than that in the control soil,and showed an increasing trend with the increase of carbon application rate as a whole.The low carbon treatment and high carbon treatment of P1 were 23.1%and 27.1%higher than that of the original soil,respectively.The same treatment of P2 increased the MBC of the soil by 49.7%and 41.7%,respectively.The content of POC in high carbon treatment and low carbon treatment in P1 was 66.9%higher than that in the control group,and the treatment with 200.2%.P2 added biochar was higher than that in the control soil,respectively.The content of particulate organic carbon increased by 22.2%and 45.8%.Although the effect of biochar on the content of LOC in the two polluted soils was smaller than that of P0,the difference was significant compared with the treatment without carbon application,and the treatment of 2%biochar in P1 was 26%higher than that in C0 treatment.The change of DOC content in the experiment group was significantly lower than that in the original soil,and the decrease of DOC content might be related to the adsorption and fixation of biochar.(3)in this study,the application of biochar produced a strong negative priming effect,and it was most significant in low-pollution soil.biochar inhibited the mineralization of soil background carbon and contributed to the fixation of soil organic carbon.This may be due to the physical protection mechanism of the adsorption of organic carbon and enzymes by biochar,the change of pH after the application of biochar into the soil,and the increase of a large number of nutrient elements,resulting in the preferential utilization of micro-organic matter to easily decomposable organic matter.Finally,the change of soil microbial quantity and community structure is the direct cause of the mineralization and decomposition of organic carbon.(4)the effects of biochar application on microbial diversity and community structure in soil were studied by using high-throughput sequencing technique.The results showed that the Shannon-Winner index of bacteria in soil after application of biochar was higher than that of the control treatment,but the difference was significant only in P2 polluted soil.After applying charcoal,the Simpson index of bacteria decreased and the diversity of bacteria in soil increased.The comprehensive analysis showed that the application of biochar increased the diversity of bacteria in soil.The Shannon-Winner index of soil fungi after carbon application was higher than that of the control,of which P2 was higher than that of the control.Compared with the control,the application of biochar increased 23.9%,the difference was significant.After carbon application,the Simpson index of fungi in the two polluted soils decreased and the difference was significant.Comprehensive analysis showed that the diversity of fungi increased after carbon application.(5)heavy metal pollution significantly affected the community structure of bacteria in soil,and the community structure of bacteria also changed significantly after the addition of biochar.Long-term heavy metal pollution has significantly changed the community structure of microorganisms in soil.The number of Trichoderma acidophilus and Microflora verrucosa in soil decreased with the increase of pollution level.The quantity of Campylobacter aeruginosa increased with the increase of heavy metal pollution.The relative abundance of P0,PI and P2 increased 1.5 times,1.11 times,60.4%,respectively,and the relative abundance of P0,P1 and P2 increased by 1.5 times,1.11 times,60.4%,respectively,and the relative abundance of P0,P1 and P2 increased by 1.56 times,1.11 times,60.4%,respectively.The relative abundance of P1 and P2 increased by 52.6%,1 1.2%and 11.5%respectively compared with the control.The relative abundance of P0,P 1 and P2 decreased by 34.2%,13.3%and 48.7%,respectively,and the difference was significant.The relative abundance of actinomycetes decreased by 46.6%,47.2%and 48.84%respectively compared with the control.The decrease extent of the relative abundance of actinomycetes increased with the increase of pollution,and the difference was significant.The effects of biochar on soil bacteria increased significantly in the order of Bacteromycetes,?-Proteus,acidobacterium and Actinomycetes.The relative abundance of Actinomycetes,?-amoeomycetes,y-Proteoses,thick-walled fungi and Bud-monocytogenes was reduced by the relative abundance of anaerobes.Long-term heavy metal pollution also had a far-reaching and significant impact on the community structure of fungi in soil.PCA analysis showed that the distribution of fungal communities in soils polluted by heavy metals was significant,and the largest group of fungi was Ascomycetes.Basidiomycetes and conjugates also vary with the degree of heavy metal contamination.Basidiomycetes and jointing fungi decreased significantly with the increase of pollution level,and the content of ascomycetes in slightly polluted P1 soil was the highest.At the same pollution level,the relative abundance of ascomycetes decreased by 7.2%,10.8%,P1 and P2,respectively,compared with the control.The relative abundance of gate was 1.4 times and 6.2 times higher than that of the control,respectively.There was no significant difference in the effect of biochar addition on fungal community structure.(5)RDA analysis showed that heavy metal pollution could significantly affect the community structure of bacteria and fungi,and the effects of Pb,Cd,Cu and Zn were synergistic.The effect of heavy metal pollution on the community structure of fungi and bacteria was significant after the application of biochar,and the available content of heavy metals in soil was opposite to the action direction of soil pH.The change of activated carbon composition also affected the microbial community structure after the addition of biochar,and the effect of POC,DOC on the community structure was just opposite to that of MBC and LOC.