Study On The Effect Of Adding Microplastics On Soil Properties And Corn Growth

With the extensive use of plastic products,micro-plastics（MPs）have become a widespread pollutant in the environment.Compared with the research on MPs in ocean and tidal flat environments,terrestrial ecosystems have just started.Studies have shown that the annual input of MPs in the soil far exceeds the input into the global ocean,and the research on the impact of MPs on farmland soil systems and crop growth characteristics and its mechanism is still in the preliminary stage of research.Therefore,it is urgent to carry out the research of MPs on the farmland ecosystem.In this study,polypropylene（PP）particles were uniformly added to the cultivation soil to simulate the current status of microplastic pollution in farmland.Using corn as the test material,a potted control experiment was used to set three dimensional variable factors of soil fertility,microplastic concentration and particle size.Among them,the microplastics concentration is set to 4 levels,namely CK（0%）,C1（0.5%,w/w）,C2（1%,w/w）and C3（2%,w/w）;Set 3 levels,the diameters are D1（<20μm）,D2（250-500μm）,D3（500-1000μm）;The soil fertility is at two levels.The low-fertilizer treatment is collected from farmland in Ansai County,Shaanxi Province without fertilization,and the high-fertilizer uses the local conventional fertilization amount,nitrogen（urea,0.15g/Kg）,potassium（K₂SO₄,0.2g/Kg）,Phosphorus（Ca（H₂PO₄）₂,0.1g/Kg）.Through research from three aspects of plant growth characteristics,soil nutrients and biological activity,the main conclusions are obtained:1.Under different fertility conditions,corn growth has different responses to microplastic pollution.Under low fertility conditions,with the increase of microplastics concentration in the treatment group with a particle size of D1,the total corn biomass decreased by 64%,84%,and 91%,while the treatment group with a particle size of D2decreased by C1 and C2.Concentration addition reduced the total biomass by 50%and 64%,and there was no significant difference in the D3 particle size treatment group relative to CK.Under high fertility conditions,the addition of microplastics did not bring significant negative effects,but the absorption of N and P by corn was significantly affected.The highest concentration（C3）of the three particle size treatment groups made the corn stems full of nitrogen and total nitrogen.The phosphorus content has been reduced by 17%,21%,22%and 50%,55%,and 34%respectively.All the microplastic addition treatments significantly increased the total carbon content of the blade.2.With the increase of the microplastic concentration in the soil,the root growth was significantly promoted.The root-to-shoot ratio of all microplastic treatment groups increased significantly under different fertility conditions,and the root surface area,volume,and average diameter all increased significantly.Among them,the smallest particle size had the greatest effect,and the high-fertilizer bar had the largest impact.The addition of C3concentration of diameter treatment makes the root volume reach 5.02±1.23cm³,and the root surface area reaches 555.9±140.1cm².3.Under high fertilizer conditions,soil nitrogen and phosphorus have a significant negative correlation with the particle size and concentration of microplastics.Soil total nitrogen（TN）,nitrate nitrogen（NO₃^--N）,water-soluble total nitrogen（TON）,microbial biomass nitrogen（MBN）,total phosphorus（TP）,and available phosphorus（AP）have a significant negative correlation.As the particle size of the microplastics decreases,the effect is more pronounced.The addition of the treatment group with a particle size of D1,D2,and the highest concentration（C3）reduces nitrate nitrogen by 52%and 41%,while available phosphorus reduces by 11%,17%.4.As the particle size of the microplastics decreases and the concentration increases,the activity ofβ-1,4-glucosidase（BG）increases significantly,among which the smallest particle size under high-fertilizer conditions（D1）The C1 and C2 concentration additions are the most significant.The BG concentration reached 11.8±0.8nmol·g^-1·h^-1,13.3±0.8nmol·g^-1·h^-1,respectively.The analysis results of water-soluble substances also showed that the water-soluble substance was completely water-soluble.Carbon（WSOC）has a significant correlation with BG and microplastic content.