Effects Of Two Fumigants On Soil Microbial Diversity And Community Structure

Fumigants are widely used in agricultural production because of their broad spectrum and strong biological activity.However,while fumigants prevent and control soil-borne pathogenic microorganisms,non-target soil microorganisms also will be affected to varying degrees.In this study,effects of two fumigants,chloropicrin(CP)and metam-sodium(MS)on the microbial community structure,diversity,dominant flora,soil nitrogen cycling and plant biological indicators were studies by means of metagenomics sequencing,real-time PCR and other biological methods,and the results are summarized as follows:(1)Effects of fumigation with CP on soil microbial community diversity and structureAfter fumigation with CP,bacterial community diversity decreased significantly.The composition structure did not change significantly at the phylum level,but a number of significantly different species in abundance were found.The predominant populations were changed.Some predominant populations significantly decreased in number or disappeared,and some new predominant populations emerged.In addition,some species associated with biodegradation,such as Sphingomonas spp.and Rhodococcus spp.,significantly increased in number.Ammonia-oxidizing archaea(AOA)populations were permanently inhibited,which may lead to inhibition of nitrification.The denitrifying population with the nosZ gene increased significantly,which was beneficial to the transition of nitrous oxide to nitrogen gas in soil.However,the relationship between the application of CP and the emission of nitrous oxide requires further exploration and research.(2)Effects of fumigation with MS on soil microbial community diversity,structure and nitrogen cyclingAfter fumigation with MS,the soil induced respiration and microbial biomass nitrogen were inhibited,and the concentration of ammonium nitrogen increased significantly;the total bacteria and fungi were significantly reduced in number,and the expression level of encoding genes of key enzymes involved in nitrogen cycling,nifH?AOA-amoA?anammox bacteria?nosZ?nirS and narG,were significantly decreased,indicating that the process of soil nitrogen cycling was suppressed.The diversity of bacterial communities decreased significantly and there was a shift in the predominant population.Due to the extremely short half-life of methyl isothiocyanate,in addition to diversity,all observed effects are transient.(3)Effects of CP and biochar on rhizosphere bacterial community diversity and structure in potted cucumber seedingsCP and biochar can promote the growth of cucumber seedings.The fumigation with CP reduced rhizosphere bacterial community diversity and changed structural composition and dominant populations,which have gradually diminished over time.The addition of biochar to the soil after fumigation with CP can promote the recovery of rhizosphere bacterial communities.These results provide a theoretical basis for the use of fumigants and biochar in agricultural production.(4)Differences of microbial community between strawberry ground soils with CP fumigation history inyears and without fumigation historyThe long-term fumigation with CP did not affect the total number of bacterial and fungal populations in soil,but reduced the number of ammonia-oxidizing bacteria(AOB)and AOA population,which will inhibit the nitrification in soil;bacterial diversity decreased significantly,while fungal diversity was not affected.Bacterial and fungal community structure changed,the relative abundance of Cyanobacteria in the bacterial community increased significantly or decreased,the number of Acidobacteria reduced significantly and Firmicutes increased significantly;The relative abundance of the Ascomycota in the fungal community reduced significantly and the relative abundance of populations of Basidiomycete,Ophiopogon,Zygomycota and some unidentified populations increased.These results provide valuable information for exploring the impact of fumigants on the sustainable development of agriculture.