Effects Of Microplastics On Cucumber Growth And Soil Nitrogen-converting Microorganism Of Farmland

At present,microplastics have become an important new pollutant in farmland ecosystems.Studies have shown that the increase of microplastics in farmland soil may affect soil nitrogen cycling and crop growth.In this study,soil from Baisha vegetable experimental site of Soil and Fertilizer Institute of Fujian Academy of Agricultural Sciences was taken as the research object.Three kinds of microplastics,including 3%polyethylene（PE）,3%polyvinyl chloride（PVC）and 3%polyethylene terephthalate（PET）were added and used to incubate cucumber in greenhouse.The effects of microplastics on cucumber growth were studied by calculating the biomass and element contents of different organs of cucumber.The effects of microplastics on soil microbial community were investigated by measuring the abundance of soil ammonia-oxidizing genes（AOAamo A,AOBamo A）,soil denitrification genes（nir S,nir K,nos Z）and the composition of ammonia-oxidizing bacteria and archaea community.The aim was to investigate the effects of microplastics on cucumber growth and nutrients cycling,and provide theoretical basis for nitrogen management in agro-ecosystem.The main results are as follows:（1）During the experiment,PE treatment significantly increased（P<0.05）leaf and root biomass of cucumber at seedling stage.PVC treatment significantly increased（P<0.05）stem biomass and total biomass of cucumber at fruiting stage.PET treatment significantly increased（P<0.05）cucumber leaf biomass at seedling stage,and significantly increased（P<0.05）cucumber total biomass at fruiting stage.PVC treatment significantly increased（P<0.05）root nitrogen content of cucumber at initial bloom stage.In addition,microplastics addition has the tendency to promote the nitrogen absorption of cucumber,and increased the leaf nitrogen content and ¹⁵N abundance.（2）PE treatment significantly increased（P<0.05）soil pH and soil NO₃^--N content at seedling stage.PE and PET treatments significantly increased（P<0.05）soil NO₃^--N content at initial bloom stage.PE and PVC treatment significantly increased（P<0.05）soil CO₂ emission,significantly inhibited（P<0.05）soil CH₄ absorption,PET and PVC treatment has the tendency to increase soil N₂O emission.（3）Microplastics addition had no significant effect on the abundance of soil AOBamo A functional gene,but PET treatment significantly decreased（P<0.05）the abundance of soil AOAamo A functional gene at initial bloom stage.PVC treatment significantly increased（P<0.05）the abundance of soil nir S functional gene at seedling stage.PET treatment significantly increased（P<0.05）the abundance of soil nir K functional gene at the fruiting stage,but significantly decreased（P<0.05）the abundance of soil nos Z functional gene at initial bloom stage.（4）Microplastics addition had little effect on soil ammonia-oxidizing archaea,but had significant effect on the composition of ammonia-oxidizing bacteria community.PET treatment increased the abundances of Acidobacteria,Nitrosospira and Nitrosovibrio of soil ammonia-oxidizing bacteria.According to redundancy analysis,soil nitrogen content was the most influential environmental factor on ammonia oxidizing bacteria composition,and followed by NO₃^--N content.In conclusion,microplastics addition increased soil pH and NO₃^--N content,increase the abundance of soil nir K and nir S functional genes,and increase the relative abundance of ammonia oxidizing bacteria in soil,thus might stimulate cucumber nitrogen absorption and growth.