Effects Of Brown Earth Properties And Fungal Community As Affected By Long-term Applying Different Rates Of Nitrogen Fertilizer

The number of soil microorganisms is huge,and the species are very important in the soil ecosystem.Among them,soil fungi is an important part of soil microorganisms,which can decompose more complex compounds,maintaining soil stability and anti-interference by forming symbiotic mycorrhizal fungi with plants to provide nutrients for crops.Nitrogen is the main limiting factor for plant growth.The application of nitrogen fertilizer will affect soil physical and chemical properties and fungal diversities.In recent years,the effects of nitrogen fertilizer application on soil functional flora have been studied extensively,but the correlation between soil fertility indicators and soil fungi is not clear.In order to further explore the effect of fertilization on soil fungi and the correlation between fertilization and soil fertility indicators,this study is based on a long-term location experiment of Brown earth at Shenyang Agricultural University(beginning in 1987),investigating the effects of different nitrogen treatments(no fertilizer,CK;nitrogen fertilizer alone,N2 and N4,urea with 135 kg N?hm-2?a-1and urea with 270 kg N?hm-2?a-1;chemical nitrogen fertilizer combined with organic fertilizer,M2N2,urea with 135 kg N hm-2a-1+ pig manure with 135 kg N?hm-2a-1;organic fertilizer alone,M4,pig manure with 270 kg N?hm-2?a-1)on the fertility indicators of Brown earth(p H,bulk density,organic matter,total nitrogen,alkaline nitrogen,available phosphorus,available potassium,total phosphorus and total potassium)and the fungi community.The results would provide a theoretical basis for guiding the rational application of chemical nitrogen fertilizer and organic fertilizer,which showed as follows:(1)Long-term non-fertilization and single application of chemical nitrogen fertilizer would be not conducive to fertilizing soil due to soil acidification and compaction,nutrient content decline.However,long-term application of organic fertilizer could alleviate the bad traits caused by single application of chemical nitrogen fertilizer,and the combined application of organic fertilizer and chemical nitrogen fertilizer could promote the balanced growth of soil fertility indicators,which was beneficial to fertilize the soil.The principal component analysis showed that there was a significant difference between organic fertilizer and chemical nitrogen fertilizer.(2)The ITS sequencing technology was used to study the changes in soil fungal communities.The number of 728,335 effective sequences with an average sequence length of334.33 bp was obtained from 15 samples.OTU clustering was performed on non-repeating sequences(excluding single sequences)according to 97% similarity.After aggregation,665 OTU representative sequences were obtained by a constitution of 1 domain,4 kingdoms,11 phyla,30 classes,70 orders,146 families,244 genera.The Sobs index,the richness and uniformity of soil fungi in different nitrogen fertilizer treatments were decreased significantly,but the indices of Shannon did not change significantly.(3)The long-term application of different nitrogen fertilizer treatments did not change the predominant fungi flora,showing they were at the phylum level of Ascomycota,but the application of nitrogen fertilizer could promote Ascomycota.The composition of the soil fungal community and the dominant fungi in different nitrogen fertilizer treatments had significantly changed.The dominant fungi in different treatments showed the Guehomyces in CK treatment with a relative abundance of 28.97%,the Pseudogymnoascus in N2 and N4 treatments with a relative abundance of 33.09% and 17.43% respectively,the Penicillium in M2N2 treatment with a relative abundance of 24.92%,and Pseudaleuria in M4 treatment with a relative abundance of 36.67%.(4)The correlation analysis results of soil fertility indicators and soil fungal communities showed that different soil fertility indicators could affect the structure of soil fungal communities.Redundancy analysis(RDA)showed that soil p H,organic matter,total phosphorus,and available potassium were the important environmental factors affecting the structural diversity of soil fungal communities.The results of variation partition analysis showed that the most explanation degree of the soil fungal community difference was by total phosphorus,while the least was by organic matter.Moreover,total phosphorus had the strongest positive correlation with Holtermanniella and the strongest negative correlation with Trichocladium.Available potassium had the strongest positive correlation with unclassified_f_Chaetomiaceae,and the strongest negative correlation with Trichocladium.p H had the strongest positive correlation with Holtermanniella and the strongest negative correlation with Cladophialophora.Organic matter had the strongest positive correlation withChaetomidium,and the strongest negative correlation with Penjcillium.(5)Function prediction by FUN Guild treated with different nitrogen fertilizers sh owed that soil fungi was mostly in Undefind Saprotroph,Animal Pathogen-Dung-Sapro troph-Endophyte-Epiphyte-Plant Saprotroph Wood Saprotroph and Animal Pathogen-Soil Saprotroph,whose relative abundances were over 50%.The proportion of unknown-fu ngi with different nitrogen fertilizers was between 15.39% and 34.86%.The evolution analysis of soil fungi in different nitrogen fertilizer treatments revealed that the 41 fu ngi evolved from the top 60 OTUs abundance contained 13 undefined genera with a r elative abundance of 31.71%.Chrysosporium differentiation was late with a complex e volution.