Effect Of Peanut Shell Biochar On Nitrification And Corresponding Microbial Mechanisms In Plastic Greenhouse Vegetable Field

In the biogeochemical cycle of soil,nitrogen,as a large number of essential elements for plant growth,directly determines its growth status.Nitrogen conversion process mainly includes nitrification,denitrification,nitrogen fixation and ammoniation.Th ese processes are mainly driven by microorganisms.Nitrification is a process in which nitrifying microorganisms oxidize ammonium nitrogen to nitrite nitrogen and then oxidize nitrate-nitrogen.It is commonly found in farmland,woodland,grassland and other terrestrial ecosystems and plays an important role in ecosystem productivity and material circulation.Due to the high multiple cropping index,the large amount of nitrogen fertilizer input,and the nitrification of the soil in plastic greenhouse vegetable field,the risk of environmental loss is high.Biochar,as a porous carbon-rich substance derived from biomass pyrolysis,has been widely concerned about the effect of soil input on nitrogen conversion and microbial activities.It is of positive significa nce to explore the law of biochar affecting soil nitrogen activities in plastic greenhouse vegetable field and to clarify the driving role of microorganisms to build efficient and safe nitrogen management decisions and prevent and control non-point source pollution in plastic greenhouse vegetable field.In this study,the soil of plastic greenhouse vegetable field in North China's fluvo-aquic soil area were used as research objects.We set up biochar gradient?the added amount of biochar was 0%for C1;0.5%for C2;1.5%for C3;4.0%for C4?soil incubation experiments,combined with chemical analysis methods,microbial molecular ecology?PCR and T-RFLP analysis technology?and high-throughput sequencing which used for observing the number of soil nitrifying bacteria and their community dynamics under the input of peanut shell biochar,analyzing the mutual assistance relationship between biochar,soil nitrification and nitrifying bacteria community,and studing the effect of biochar on soil nitrification in plastic greenhouse vegetable field and its microbiological mechanism?ammonia oxidizing archaea AOA,ammonia oxidizing bacteria AOB and nitrite oxidizing bacteria NOB?systematically.The main results obtained are as follows:?1?The addition of biochar significantly increased soil TN?Total Nitrogen?and SOM?Soil Organic Matter?contents?P<0.01?and reduced soil p H value and EC?Electrical Conductivity?.Compared with non-addition?C1?,TN increased by 23.21%-45.32%,SOM increased by 18.51%-53.34%,and p H and EC decreased by 0.03-0.24 units,0.46-0.88 ms/cm,respectively.Biochar treatment?C2,C3 and C4?increased MBC?Microbial Biomass Carbon?by 3.20%-16.55%compared with C1,and MBN?Microbial Biomass Nitrogen?increased by 7.25%-32.40%,respectively.When biochar was added to promote soil nitrification,the initial ammonium nitrogen?NH₄⁺-N?content decreased by 13.41%-31.12%,the accumulation of nitrate nitrogen?NO₃^--N?increased by 1.72%-25.63%,the oxidation activity of nitrite in soil increased by 18.12%-44.34%,and the net nitrification rate increased by 21.81%-70.23%,which compared to the treament without biochar.?2?At the initial stage of biochar input,the gene abundance of AOA amo A was significantly increased,and that of AOB amo A was significantly increased at the later stage.Compared with?C1?,AOAamo A abundance in C2,C3 and C4 treatments increased by 26.31%,37.32%and 40.23%,and AOB amo A abundance increased by 48.94%,53.32%and 26.51%,respectively.The Shannon index of AOB community increased by 5.44%-18.82%and Evennes index by 26.21%-33.86%at the initial stage,and Shannon index decreased by 15.01%-28.63%at the later stage.The fragments of 256bp,58bp,21bp and 491bp in AOB community represented the increase of species abundance,and 488 bp represented the decrease of species abundance.Under the condition of biochar input,it was found that the changes of soil p H,OM,MBN and TN were the main environmental factors causing the increase of AOB community structure.There was no significant effect on AOA community during the whole incubation process.?3?At the late stage of biochar input,the nxr A gene abundance was significantly increased by4.42%-40.41%;at the early stage,the Shannon index of Nitrobacter-like NOB community was increased by 7.69-15.05%;at the later stage,it was increased by 0.30%-11.41%.The biochar application also increased the abundance of OTU193 which belonged to Nitrobacter?alkalicus and OTU42,OTU308,OTU229 and OTU258 which belonged to Nitrobacter?vulgaris in the community of Nitrobacter-like NOB.Under the conditions of biochar input,MBN and NO₃^--N were the main environmental factors affecting NOB community structure.The community of Nitrospira-like NOB was not significantly affected during the whole process.Results by above knowable,biochar input by reducing the soil p H,NH₄⁺-N and EC,and significantly increasing the SOM,NO₃^--N and TN,improved soil microenvironment,increased the abundance of nxr A genes of NOB and amo A gene of AOA and AOB,and optimizd AOB and Nitrobacter-like NOB communities The structure improved soil nitrite oxidation activity and net nitrification rate,promoted soil nitrification and accelerates soil nitrogen conversion rate.