Effects Of Different Fertilization Patterns On Soil Microbial Community And N Cycle In Greenhouse Vegetable Production

As a highly intensive cultivated system with high-input and high-output,there are several widespread phenomena(e.g.,excessive application of fertilizers,improper selection of organic manures/materials,and imbalance in the proportions of combined application of organic manures and chemical fertilizers)in greenhouse vegetable production systems(GVPs)in China.These phenomena lead to a series of problems in soils,such as excessive accumulation of nutrients(N and P,etc.),decrease of organic matter,and the destruction of soil microbial community structure,which seriously restricts the sustainable development of GVPs in China.Soil microorganisms are vital components in agroecosystems;meanwhile,they are crucial indices for reflecting soil health and fertility.As an essential nutrient element for crop growth,N is a key factor limiting crop growth and yield.The soil N cycle is an important element cycle in the ecosystem,which include two main processes of N transformation,i.e.,Nitrification and denitrification.Soil microorganisms are important carriers and media for driving N cycle in soils.With the rise of metagenomic sequence technology,we have a deeper understanding of soil microbial community composition and its functional metabolism.The full-fruit stage is a critical stage for the growth of spring tomato in GVPs.During this stage,tomato has a high demand for soil nutrients and soil microbial metabolism is strong.Based on a ten-year fixed-site fertilization experiment located in Xiqing District,Tianjin City,we preliminarily explored the response of microbial biomass,enzyme activities,microbial community structure,and N cycle functional gene in soils to different fertilization patterns at the full-fruit stage of spring tomato in GVPs.The obtained results are summarized as follows:1.Partial substitution of chemical fertilizer with organic amendments,especially straw-amended treatments,could increase the contents of microbial biomass C(MBC),N(MBN)and enzyme activities.The contents of MBC and MBN at the full-fruit stage of spring tomato in GVPs were increased in organic-amended soils by average of 101.5%and 134.6%,respectively,compared with those in 4/4CN treatment.Moreover,the contents of MBC and MBN in straw-amended soils were higher by average of 158.8%and210.9%,respectively,than those in 4/4CN treatment.The activities of?G,?G,CBH,XYL,and NAG were increased in organic-amended soils by average of 128.8%,179.9%,388.4%,215.3%,and 247.3%,respectively,compared with those in 4/4CN treatment.Moreover,these enzyme activities in straw-amended soils were higher by average of 26.2%,337.3%,702.9%,358.9%,and 457.0%,respectively,than those in 4/4CN treatment.Notably,soil nitrate N and organic C were main dominant soil factors for influencing the changes in soil microbial biomass and enzyme activities.2.Partial substitution of chemical fertilizer with organic amendments could increase bacterial and fungal abundance,decrease archaea'abundance,alter soil dominant flora composition,and increase microbial diversity in soils.At the full-fruit stage of spring tomato in GVPs,organic-amended treatments induced higher abundances of bacteria and fungi by average of 8.6%and 11.6%,respectively,and lower abundance of archaea by average of 21.7%than those in 4/4CN treatment.At the phylum level of bacteria,organic-amended treatments had higher relative abundance of Proteobacteria,and lower relative abundance of Actinobacteria and Chloroflexi than those in 4/4CN treatment.Among the main dominant fungal taxa,organic-amended treatments induced higher relative abundance of Ascomycota,Chytridiomycota and Glomeromycota,and lower relative abundance of Basidiomycota than those in4/4CN treatment.Among the main dominant archaea taxa,organic-amended treatments resulted in higher relative abundance of Euryarchaeota and Candidatus Bathyarchaeota,and lower relative abundance of Thaumarchaeota than those in 4/4CN treatment.Partial substitution of chemical fertilizer with organic amendments,especially 2/4CN+1/4MN+1/4SN treatments,contained higher values of the indices of diversity and richness for soil bacteria,fungi and archaea than those in 4/4CN treatment.The results of principal component analysis showed that the archaea'community composition is strongly influenced by fertilization compared with the bacterial and fungal community composition.Redundancy analysis(RDA)revealed that nitrate N and organic C were main dominant factors for driving the changes of soil bacteria,fungi and archaea.3.Partial substitution of chemical fertilizer with organic amendments could increase soil potential nitrification rate(PNR)and N₂O cumulative emission fluxes,alter the composition of soil N cycle function gene.At the full-fruit stage of spring tomato in GVPs,the PNR and N₂O cumulative emission fluxes were increased in organic-amended treatments by average of 72.9%and 59.6%,respectively,than those in 4/4CN treatment.Compared with 4/4CN treatment,organic-amended treatments could decrease the abundance of functional genes for nitrification and nitrogen fixation,increase the abundance of functional genes for denitrification,dissimilatory nitrate reduction,and assimilatory nitrate reduction.The results of Pearson correlation analysis revealed that soil p H and nutrient indices(i.e.,organic C and ammonium N)were significantly negatively or positively correlated with PNR,respectively.Meanwhile,soil organic C and nitrate N were significantly positively correlated with soil N₂O cumulative emission fluxes.The redundancy analysis revealed that soil nitrate N and ammonium N had strong effects on soil N cycle functional microorganisms.