Study On The Response Mechanism Of Soil Enzymes And Microorganisms To Microplastics From Mulching Film Residue In Farmland

In recent years,the pollution of microplastics（MPs）has become a serious global environmental problem.In agricultural production,the use of plastic films leads to the long-term presence of MPs in soil,which will inevitably have some impact on soil environmental quality.Soil enzymes and microorganisms,as important components of soil,respond rapidly to changes of soil environmental quality and are important indicators of soil biochemical processes,but studies on the response of soil enzymes and microorganisms to MPs are still limited.Therefore,we investigated the effects of different concentrations（0%,1%,5%,10%）of MPs on the enzymatic reaction characteristics and microbial community diversity of degrade black soil（S1）,alkaline black soil（S2）and black submerged soil（S3）in northeast China through soil incubation tests,and analyzed their relationships with soil physicochemical properties to clarify the enzymatic and microbial response mechanisms of different types of soils in northeast China to ground film MPs.To investigate the influence of MPs on the quality of farmland soil environment from the perspective of soil microbiology,and to provide a basis for the maintenance of farmland soil health and productivity.The following results were obtained from the study:（1）The effects of MPs on the physicochemical properties of the three different soils in Northeast China were different,with a trend of increasing and then decreasing or gradually decreasing soil physicochemical properties with increasing MPs concentration.Compared with the control,MPs treatment decreased the pH of S1 and increased the pH of S3,while the pH of S2 remained unchanged.MPs decreased the SOM content of S1and S3s but had less effect on the TN content,while the TN content of S2 increased and the SOM content remained unchanged,and decreased the TP content of three soils,resulting in a decrease in C:N and C:P of S1 and S3,while the C:N of S2 remained unchanged.However,the C:P of S2 and the N:P ratio of all three soils increased;the change patterns of AN and AP content of the three soils were relatively consistent,with AN content increasing at low concentrations（1%）and decreasing at other concentrations,and all AP content decreasing.（2）The differences in the effects of MPs on the activities of catalase（CAT）and hydrolases（INV,URE,and PHO）of the three soils in northeast China were large,with soil CAT showing a strong concentration effect,while the three hydrolases activities and showed no concentration effect on MPs.Compared with the control,MPs increased the CAT of S1,while S2 and S3s increased only at 1%concentration and decreased at the rest of the concentrations.Both INV and URE of S1 decreased,while S2 and S3 showed greater variation in the activity of the 2 enzymes,but when the concentration of MPs reached 10%,all soil enzyme activities decreased.The effects of MPs on the activity of all 3 soil PHO were small.（3）The differences in the effects of MPs on the kinetic parameters(K_m,V_max,V_max/K_m)of different enzymes in the three northeast soils were large,and all four enzymes showed a strong concentration effect.Compared to the control,all concentrations of MPs increased the V_max/K_m of S1 CAT,while K_m and V_max varied in waves at different concentrations.K_m and V_max increased and V_max/K_m decreased in both S2 and S3s.MPs decreased K_m and V_max and increased V_max/K_m of S1 CAT;S2 and S3 CAT kinetic parameters changes were opposite to S1.MPs decreased V_max of URE in three soils without regular changes in K_m and V_max/K_m.MPs increased K_m,V_max of PHO in S1 and S3s while V_max/K_m mostly decreased in S2 in contrast to the other two soils.（4）MPs had different effects on the diversity of bacterial communities in 3northeastern soils.Compared with the control,MPs changed the species abundance of the three soils,reduced the S1α-diversity（ACE index,Chao1 index,Shannon index）,while theα-diversity of S2 and S3s increased or remained unchanged at different MPs concentrations.MPs didn’t change the dominant phylum of the three soils,but only the relative abundance of the dominant phylum.MPs reduced the functional abundance of metabolism,genetic information processing and cellular processes in S1,but no change the soil functions in S2,while S3 only behaved differently under different concentrations of MPs treatment.（5）After MPs treatment,the physicochemical properties,enzyme reaction characteristics andα-diversity of the three different soils showed some correlations,but the correlations were different for different types of soils.MPs treatment changed the fertility composition of the soils,and the main factors in soil 1 were pH,CAT,AP,SOM,and URE-V_max,in soil 2 were SOM,Shannon index,PHO-V_max/K_m,PHO,and CAT-V_max,and in soil 3 were ACE index,Shannon index,CAT-V_max/K_m,CAT,and TP.