Separation And Selection Of Heterotrophic Nitrifying Bacteria From Lawn Soil And Their Nitrification Capacity Characteristics In Different Nitrogen Sources

Turf soil is an artificial vegetation with high nutrient demand.A large number of chemical fertilizers are applied to maintain nutrient supply every year,which not only improves maintenance costs,but also leads to environmental pollution.Heterotrophic nitrification refers to the process of converting soil reductive nitrogen into nitrate and nitrite which is available for plants by heterotrophic microorganisms.This process can increase soil nitrogen supply capacity.In recent years,the regulatory role of heterotrophic nitrification in soil nitrogen conversion has attracted much attention.Using heterotrophic nitrifying microorganisms to improve soil nutrient supply capacity has become an important research topic to control agricultural fertilizer pollution,and is also expected to be one of the important measures for agricultural reduction.As there are relatively few investigations and researches in this field,many mechanisms such as the species and functions of heterotrophic nitrifying microorganisms,nitrification characteristics,nitrification products,nitrogen loss,and gas emissions characteristics are still unclear.In this experiment,two heterotrophic nitrifying bacteria isolated from lawn soil and were identified by comparing 16S rDNA sequence to homologous species which has been published on the GenBank.With inorganic nitrogen（ammonium）,low-molecular-weight organic nitrogen（glycine,glutamic acid and lysine）and mixed nitrogen（amino acid and ammonium）as nitrogen sources,the nitrification ability,intermediate products and N₂O emission characteristics of two strains in different nitrogen sources were tested under constant temperature in order to provide a theoretical basis for clarifying the utilization capacity and nitrification mechanism of heterotrophic nitrifying bacteria with different nitrogen sources.The main results are as follows:1.Two heterotrophic nitrifying bacteria were isolated and they were neither spore nor flagella,one was white,and the other was opaque milky white.SEM images shows that two strains were short rods,the sizes are（0.7-0.9）×0.5μm and（1.0-1.2）×0.5μm,respectively.These two heterotrophic nitrifying bacteria were identified as Pseudomonas sp.,16S rDNA fragment length were 1448 bp and 1460 bp and named as Pseudomonas sp.BJ and Pseudomonas sp.DJ respectively.GenBank accession number were MF001078 and MF001079 for Pseudomonas sp.BJ and Pseudomonas sp.DJ.2.Both of two strains have a strong nitrification ability with inorganic nitrogen,and the utilization rates of ammonium nitrogen were 96.82%and 97.06%,respectively.There was no significant difference in the nitrification ability between two strains with inorganic nitrogen.Hydroxylamine and nitrate content peoduced by strain DJ were significantly higher than that of strain BJ in the inorganic nitrogen nitrification process.3.Strain BJ had the lowest utilization rate with glutamic when organic nitrogen was nitrogen source.（P<0.05）,while strain DJ had the highest utilization rate with glutamic（P<0.05）.The utilization rate of strain DJ with Glutamic was significantly higher than that of strain BJ（P<0.05）.There was no significant difference in the utilization with glycine and lysine between two strains.Strain BJ had the highest utilization with glutamic（P<0.05）,and there was no significant difference in the utilization with lysine and glycine.The utilization rate of strain DJ in glycine was higher than in lysine,and utilization rate in lysine acids of strain DJ was greater than glutamic（P<0.05）.The utilization of ammonium nitrogen of both strains in mixed nitrogen sources was lower than that in inorganic nitrogen（P<0.05）.Ammonia nitrogen utilization of Strain BJ was higher than that of strain DJ in mixed nitrogen sources.4.In the nitrification process with inorganic nitrogen,the total N₂O emissions of strain BJ was significantly higher than that of strain DJ（P<0.05）.The amount of N₂O content of strain DJ was the highest with glycine during six days of cultivation（P<0.05）.There was no significant difference in the amount of N₂O emissions produced by the strain BJ with three kinds of amino acids and strain DJ with lysine and glutamate.