Effects Of Two Types Of Typical Pesticides On Composition,Function And Structure Of Soil Microbial Communities

Pesticides are an important means in agricultural production and play an important role in preventing and controlling agricultural pests with the use of ensuring agricultural production safety.However,the soil pollution caused by excessive and unreasonable use of pesticides is becoming more and more serious.According to the registration information of newly registered pesticides from 2013 to 2020,the ratio of pesticide registrations has continued to decline,while the ratio of fungicides and herbicides has slowly increased.Studies have shown that the use of pesticides will affect the activities of soil microorganisms.Soil microorganisms are sensitive and rapid in response to environmental changes,which made it could be used as important biological indicators to evaluate soil quality.Therefore,it is particularly important to study the ecological effects of two types of typical pesticides,fungicides and herbicides on soil microorganisms.For fungicides,azoxystrobin,as a representative of this type of fungicide,has become the world's number one agricultural fungicide.For herbicides,atrazine is a triazine herbicide,which is a selective systemic conduction pre-emergence and post-emergence herbicide.At present,atrazine is one of the most widely used herbicides in the world.The widespread use of the two pesticides will inevitably bring certain ecological risks to the environment,and the environmental effects of the two pesticides have also attracted widespread attention.However,most of the current researches on both are carried out indoors,and it is very important to carry out research in the actual environment.In addition,new fungicides and herbicides are constantly being updated.Trifloxystrobin,as another important species of strobilurin fungicides,has developed rapidly.In the field of herbicide research and application,triazolopyrimidine sulfonyl herbicides represented by pyroxsulam are the best developed in recent years,and the most promising class of ALS inhibitor herbicides.At present,research on the ecotoxicological effects of these two pesticides is still in its infancy.However,after the expiration of the patent protection of these two pesticides,it will lead to large-scale production and use in my country,which will be followed by environmental problems.Its eco-toxic effects on soil microorganisms are not yet clear.Based on the above,this study selected two types of typical pesticide herbicides and fungicides as the research objects,combined with the actual use of each pesticide in production and life,selected atrazine and azoxystrobin to carry out field trials;the indoor simulation test of pyroxsulam and the trifloxystrobin was carried out.The population number of soil microorganisms,fungi,and actinomycetes,soil enzyme activities,the abundance of functional genes related to the N and C cycles in the soil,and the changes in soil community structure were detected to reflect eco-toxic effects on soil microorganisms.The results will enrich relevant toxicological data and provide theoretical basis for environmental safety risk assessment and guiding the rational use of pesticides.The main findings of this paper are as follows:(1)Both azoxystrobin and trifloxystrobin significantly inhibit the number of soil fungi,and have little effect on the number of soil bacteria and actinomycetes;both atrazine and pyroxsulam has an inhibitory effect on the number of soil bacteria,fungi and actinomycetes,but as time goes by,the inhibitory effect gradually recovers.(2)The fungicides azoxystrobin and trifloxystrobin have little effect on soil urease,and inhibit dehydrogenase activity.The effects on ?-glucosidase are greatly affected by environmental factors.both atrazine and pyroxsulam could promote soil urease activity and have little effect on soil dehydrogenase.The addition of pyroxsulam will promote?-glucosidase activity.For changes in the abundance of specific functional genes,azoxystrobin,trifloxystrobin,atrazine,and pyroxsulam all have an inhibiting effect on the abundance of soil nitrogen cycle-related genes(AOA-amo A,AOB-amo A,nir K,nir S,and nif H)and the abundance of carbon fixation genes(cbb LR,cbb LG).(3)According to the influence of various pesticides on the dominance phylum of soil bacteria,the addition of azoxystrobin,trifloxystrobin,atrazine and pyroxsulam will all affect the dominance of soil bacteria and change the structure of soil community.The principal component analysis of the soil community structure also illustrates this result.(4)The addition of azoxystrobin made the abundance of Gp4,Gp6,and Luteimonas which have the function of degrading cellulose in the soil first decrease and then increase.The addition of azoxystrobin(wheat field)and atrazine lead the abundance of Gemmatimonas,which are important in the denitrification process,first decreased and then increased.Under the influence of trifloxystrobin,the abundance of Gemmatimonas and Kribbella had been changed,which plays an important role in the denitrification process,indicating that the addition of trifloxystrobin will affect the soil nitrogen cycle.The addition of pyroxsulam caused the abundance of Nitrospira that participates in soil nitrification and Haliangium that participates in soil denitrification first decreased and then increased,indicating that the addition of pyroxsulam will have varying degrees of impact on the soil nitrogen cycle.(5)By analyzing the interaction of various pesticides on soil microorganisms,it can be seen that the addition of atrazine has no effect on the positive and negative correlations between soil microorganisms,which means,atrazine has little effect on the interaction between soil microorganisms;the addition of azoxystrobin,trifloxystrobin,and pyroxsulam at high concentrations all resulted in a significant increase in the positive correlation between soil microorganisms,that is,the addition of azoxystrobin,trifloxystrobin,and pyroxsulam at high concentrations promoted soil microorganisms co-evolutionary relationship.(6)By comparing the sensitivity of soil microbial quantity,soil enzyme activity,soil functional microbes to the response of various pesticides,it can be found that the number of soil fungi,urease,and denitrification genes nir K and cbb LG are the most sensitive indicators to the response of various pesticides among various indicators.