Effects Of 7-Year Plastic Film Mulching And Nitrogen Application On AM Fungal And Rhizosphere Bacterial Community

Arbuscular mycorrhizal(AM)fungi and rhizosphere bacteria are important soil microorganisms which can form a mutually symbiotic relationship with plant roots.They play a key role in promoting plant growth and development,enhancing plant stress resistance,and maintaining agroecosystem stability.Plastic film mulching(PFM)and nitrogen(N)fertilization are of great significance to the growth and development of crops,biomass accumulation and soil properties,while there are few studies that AM fungi and soil bacteria community structure and function responding to PFM and N.This study investigated how 7-year(2012-2018)PFM and N application treatment impacted root AM fungi and rhizosphere bacterial diversity and community characteristics in field conditions on the Loess Plateau.Six treatments were set up,including no PFM without N fertilizer(M0N0),no PFM with N fertilizer(M0N1),PFM without N fertilizer(M1N0)and PFM with N fertilizer(M1N1),all of which maize was grown in;the other two including no planting with and without PFM.The main findings are as follows:1.Regardless of PFM or N application,the gene sequences obtained at the genus level of the corn root AM fungal community belong to Glomus,Diversispora,Ambispora and unclassified.Glomus(62.12%-99.49%)had the highest relative abundance,exceeding 60% in all treatments.Diversispora(0.43%-37.86%)also appeared in all treatments,but the relative abundance was low.At 0-20 cm soil layer,Ambispora only existed in M1N1(0.19%),M1N0(2.57%)and M0N1(0.11%)treatments,and unclassified only appeared in M0N1(0.01%)and M0N0(0.02%)treatments.At 20-40 cm soil layer,Ambispora and unclassified only appeared in M1N0(0.66%,0.34%)and M0N0(0.60%,0.01%)treatments.N application increased the relative abundance of Glomus and reduced the relative abundance of Diversispora at 0-20 cm depth(P<0.05).Glomus and Diversispora which were not affected by PFM at 0-20 and 20-40 cm soil layers.PFM had no effect on the richness and diversity index of AM fungi at 0-20 and 20-40 cm soil layers while N application significantly increased AM fungi diversity index at 0-20 cm soil layer.N had no effect on the richness and diversity index of AM fungi at 20-40 cm soil layer.2.At 0-20 cm soil layer,the gene sequence obtained by the rhizobacterial community at the genus level can be divided into 576 genera,and the top 11 bacterial groups in relative abundance are Micrococcaceae,Acidobacter,JG30-KF-CM45,Nocardioides,KD4-96,Solirubrobacter,Gemmatimonadaceae,Sphingomonas Blastococcus,Paenarthrobacter,Actinobacteria.N fertilization significantly reduced the relative abundance of Gemmatimonadaceae and JG30-KF-CM45,but increased in the case of Paenarthrobacter.At 20-40 cm soil layer,the gene sequence obtained by the rhizobacterial community at the genus level can be divided into 573 genera,and the top 11 bacterial groups in relative abundance are Micrococcaceae,Acidobacter,Actinobacteria Gaiellales,Gemmatimonadacea,KD4-96,Bacillus,Gitt-GS-136,Gaiella,Acidimicrobiales,Nitrospira.N fertilization significantly reduced the relative abundance of Gaiellales and Gaiella.PFM had no effect on the richness and diversity index of rhizobacteria at 0-20 and 20-40 cm soil layers.N fertilization significantly decreased bacterial diversity but N had no significant effect on the richness of rhizosphere bacteria at 0-20 cm soil layer.N had no effect on the richness and diversity index of AM fungi at 20-40 cm soil layer.3.PICRUSt analysis of functional gene prediction were used to characterise functional component involved in N cycling and soil carbon(C)degradation.At 0-20 cm soil layer,PFM increased the abundance of denitrification gene narG(P=0.048).Predicted N cycling genes(nitrification gene Hao and denitrification gene napA,P=0.011 and P=0.030,respectively)increased with N application.N application increased the abundance of hemicellulose degrading gene ?-galactosidase(P=0.002)and lignin degrading gene Catalase(P=0.015),but decreased the abundance of cellulose and chitin degrading gene Endoglucanase(P=0.002)and Chitinase(P=0.009).PFM and N had no effect on the abundance of C and N cycling genes at 20-40 cm soil layer.The causal relationship SEM model utilizing relevant variables such as soil physical and chemical properties,plant properties,AM fungal and bacterial community could explain 69%,94%,61% and 32% of the variance in soil physical and chemical properties,plant properties,AM fungal community and rhizosphere bacterial community.PFM mainly affected AM fungal community by indirect effects,while PFM affected the rhizosphere bacterial community by both direct and indirect effects.The direct effects of N fertilization on rhizosphere bacterial community was stronger than AM fungi community.Our findings highlight the importance of plastic film mulching and nitrogen in modifying AM fungi community structure,rhizosphere bacterial community structure and abundance of functional genes associated with C and N cycling in the soil.It emphasizes that long-term PFM would potentially increase denitrification and N fertilization would change the level of C metabolism in the soil,and then,which would influence the stability and sustainability of farmland ecosystems.A relatively stable interaction relationship would be formed among roots,microorganisms and soil environmental factors.It provides a theoretical basis for improving the farmland ecological environment in the semi-arid area of the Loess Plateau,maintaining the sustainable development of agriculture in this area and protecting the soil microbial community.