Effects Of Neonicotinoids On Soil Microorganisms And Collembola

Neonicotinoid is a new kind of insecticides with a structure resembling nicotine,and it is widely used around the world.It has a long half-life,so if it is used for a long time,it will accumulate in soil and pose a potential threat to the soil ecology.Although it has been reported that it has certain harmful effects on bees,aquatic arthropods,moths,etc.,the research on its influence in soil is still at a blank stage.This study mainly includes:1)incubation experiments of adding two different neonicotinoids with different concentration gradients to two different types of soil(sand loam and clay),research on the effects of neonicotinoids on soil microbial activity and community composition by high-throughput sequencing and other techniques;2)Adding neonicotinoids,13C labeling maize and collembola in the two soils,using 13C isotope labeling technique to explore the effects of neonicotinoids on the maize mineralization through the "collembola-microbes" food chain.The main conclusions are as following:(1)The high concentration of dinotefuran significantly reduced microbial biomass carbon in sand loam.This inhibition was weakened to a certain extent after the addition of maize.However,at low concentrations,this inhibitory effect on microorganisms did not appear.For imidacloprid,even at high concentrations,there is no significant effect on microbial biomass carbon,whether or not there is an additional carbon source.After the addition of dinotefuran in sand loam,the soil respiration was promoted and then inhibited,after the addition of maize,the promotion effect disappeared,the pesticide only inhibited the soil respiration with maize,and the higher the concentration of pesticide was,the stronger the inhibitory effect was.After adding dinotefuran in clay,soil respiration was promoted and reached the highest at 50 ?g·kg-1 soil concentration.Imidacloprid had little effect on soil respiration,only a small degree of promotion.(2)After the addition of dinotefuran,the 16s rRNA gene sequence analysis showed that the bacterial community structure changed significantly in both two soils.Especially in sand loam,bacterial diversity and community composition were significantly changed at both three concentrations.There was a significant change in the relative abundance of the six phyla of both soils after the addition of dinotefuran,of which the microbiology department responded most at the family levels of Acidobacteria and Actinobacteria.(3)Both neonicotinoids significantly reduced the survival and reproduction rate of collembola,and dinotefuran inhibited exogenous carbon assimilation of collembolan.The addition of pesticides had no significant effect on MBC and 13C-MBC,but significantly increased the total release of CO2 and inhibited 13C-CO2 efflux significantly in clay.The addition of dinotefuran significantly affected some dominant flora of fungi and bacteria,but did not affect the flora with significant correlation with 13C-MBC and 13C-CO2,which also explained the reason why there was no significant difference in 13C-MBC and 13C-CO2 after the addition of dinotefuran.