Patent Publication Number: US-2022220538-A1

Title: Method for rapidly detecting the total nitrogen content of the soil in an urban green land by using archaea molecular marker otu300

Description:
TECHNICAL FIELD 
     The present invention belongs to the field of biotechnology and relates to a method for rapidly detecting the total nitrogen content of the soil in an urban green land by using archaea molecular marker OTU300. 
     BACKGROUND 
     The construction of urban landscaping is an important part of the construction of ecological civilization and a good environment. It plays an important role in optimizing the urban environment, improving the quality of life of the people, and promoting the sustainable development of the city. As the material basis of the urban ecological environment, the quality of the urban green land soil directly affects the healthy growth of plants and the performance of ecological benefits and landscape functions, and to a certain extent determines the quality of urban green land. Therefore, scientific and objective monitoring and evaluation of soil quality is an important reference basis for the management of urban green lands. 
     At present, the detection of soil quality indicators in urban green land mainly follows traditional physical and chemical detection methods, which require a lot of samples, a complicated pretreatment process, a long cycle, and a high cost on human resources. So, it is difficult to achieve rapid detection of large quantities of samples. Soil microorganisms have comprehensive, sensitive, and functional characteristics to the changes in the soil environment. It is of great practical significance to explore the rapid and automatic detection technology for soil quality indicators in urban green land by detecting the abundance of specific microbial groups. 
     The soil total nitrogen is an important indicator of soil fertility quality. Soil total nitrogen includes all forms of organic and inorganic nitrogen, and it is a source and store pool that marks the total amount of soil nitrogen and supplies available nitrogen to plants. It can comprehensively reflect the status of soil nitrogen and can be used to assess soil nitrogen supply capacity. Soil total nitrogen is affected by natural factors such as soil-forming parent material, geography, climate, organisms, and human factors such as greening maintenance. Its distribution in soil shows significant spatial heterogeneity. The soil total nitrogen has become a routine item of soil quality analysis and laboratory measurement in various countries. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a method for rapidly detecting the total nitrogen content of the soil in an urban green land by using archaea molecular marker OTU300. 
     The present invention provides a primer-probe set, which is composed of a specific primers pair and a specific probe; the specific primers pair consists of the primer 524F-10-ext shown as SEQ ID NO. 4 of the sequence listing and the primer Arch958R-mod shown as SEQ ID NO. 5 of the sequence listing; the nucleotide sequence of the specific probe is shown as SEQ ID NO. 1 of the sequence listing. The specific probe is a Taqman probe. The Taqman probe has a fluorescent group at its 5′end and a fluorescence quenching group at its 3′end. The fluorescent group may specifically be FAM. The fluorescence quenching group may specifically be TAMRA. 
     The present invention also claims the application of the primer-probe set in detecting or assisting in detecting the total nitrogen content of the soil. 
     The present invention also claims the application of the primer-probe set in comparing the total nitrogen content of the soil in different plots. 
     The present invention also claims a kit, which comprises the primer-probe set. 
     The function of the kit is as follows (a) or (b): 
     (A) Detecting or assist in detecting the total nitrogen content of the soil; 
     (B) Comparing the total nitrogen content of the soil in different plots. 
     The kit also includes a carrier that records Method A or Method B as described below. 
     The present invention also provides a DNA molecule (probe), shown in SEQ ID NO. 1 of the sequence listing. 
     The DNA molecule (probe) may or may not be labeled with a label. The label refers to any atom or molecule that can be used to provide a detectable effect and can be attached to a nucleic acid. The Label includes but not limited to dyes; radiolabels, such as 32P; binding moieties, such as biotin; haptens, such as digoxin (DIG); luminescent, phosphorescent, or fluorescent moieties; and fluorescent dyes alone or fluorescent dyes combined with moieties, of which the emission spectrum can be suppressed or shifted by fluorescence resonance energy transfer (FRET). The labels can provide a signal that can be detected by fluorescence, radioactivity, colorimetry, gravimetry, X-ray diffraction or absorption, magnetism, enzyme activity, and so on. The labels can be a charged moiety (positive or negative) or optionally, can be neutral. The labels may include a nucleic acid or protein sequence or a combination thereof, as long as the sequence containing labels is detectable. In some embodiments, directly detect the nucleic acid without the label (e.g., read the sequence directly). 
     The present invention provides a Taqman probe, its nucleotide sequence shown as SEQ ID NO. 1 of the sequence listing. The Taqman probe has a fluorescent group at the 5′end and a fluorescence quenching group at the 3′end. The fluorescent group may specifically be FAM. The fluorescence quenching group may specifically be TAMRA. 
     The present invention also claims the application of the DNA molecule or the Taqman probe in detecting or assist in detecting the total nitrogen content of the soil. 
     The present invention also claims the application of the DNA molecule or the Taqman probe in comparing the total nitrogen content of the soil in different plots. 
     The present invention also provides a method (Method A) for detecting total nitrogen content in the soil, which includes the following steps: 
     Using the total DNA of the soil sample as a template to perform real-time fluorescent quantitative PCR; The amplification primer pair of real-time fluorescence quantitative PCR is composed of primer 524F-10-ext shown as SEQ ID NO. 4 of the sequence listing and primer Arch958R-mod shown as SEQ ID NO. 5 of the sequence listing. The nucleotide sequence of the probe for real-time fluorescence quantitative PCR is shown as SEQ ID NO. 1 of the sequence listing. 
     The Ct value is obtained by real-time fluorescent quantitative PCR; the copy number is calculated according to the Ct value, and the total nitrogen content in the soil sample is calculated by the copy number content in the soil sample. 
     The probe of real-time fluorescent quantitative PCR is Taqman probe. The Taqman probe has a fluorescent group at the 5′end and a fluorescence quenching group at the 3′end. The fluorescent group may specifically be FAM. The fluorescence quenching group may specifically be TAMRA. 
     The copy number is the copy number of the target fragment of the probe. 
     The method for calculating the total nitrogen content in the soil sample by calculating the copy number content in the soil sample is: substituting the copy number content of the soil sample into a linear equation to obtain the total nitrogen content of the soil sample. 
     The linear equation is y=0.0361x+0.6785; R 2 =0.9151; y represents total nitrogen content, and the unit is g/kg; x represents copy number content of target OUT, and the unit is ×10 6  copies/g. 
     The method of calculating the copy number based on the Ct value is: Substituting the Ct value into the standard curve equation to obtain the copy number. 
     The preparation method of the standard curve equation is: ligate the DNA molecule shown as SEQ ID NO. 2 of the sequence listing to the pMD18-T vector to obtain OTU300 standard plasmid; and use the OTU300 standard plasmid to produce a standard curve equation with the logarithm of the copy number as the independent variable and Ct as the dependent variable. The logarithm of the copy number is the logarithm with base 10 of the copy number. 
     Preparation method of total DNA of soil samples: adopt MoBioPowerSoil® DNA Isolation Kit (MoBio Laboratories, Carlsbad, Inc., CA, USA) to extract total DNA of soil samples. 
     The real-time fluorescent quantitative PCR is performed on LightCycler® 96 real-time fluorescent quantitative PCR instrument. 
     The real-time fluorescent quantitative PCR reaction system (20 μL) is: 10 μL Premix Ex Taq (Takara, Dalian, China), 0.4 μL primer 524F-10-ext, 0.4 μL primer Arch958R-mod, 0.2 μL probe, 2 μL template solution and 7 μL sterile water. In the reaction system, the concentration of primer 524F-10-ext is 0.2 μM, the concentration of primer Arch958R-mod is 0.2 μM, and the concentration of probe is 0.1 μM. In the reaction system, the content of template DNA is 7 ng. 
     The real-time fluorescent quantitative PCR reaction program is pre-denaturation at 95° C. for 120 s; denaturation at 95° C. for 10 s, annealing extension at 60° C. for 45 s, 45 cycles. 
     The present invention also provides a method for comparing the total nitrogen content of the soil in different plots (Method B), which includes the following steps: 
     testing the soil samples of more than two plots according to Method A; 
     comparing the total nitrogen content in the soil of each plot based on the test results. 
     Any of the above-mentioned soil is green land soil. 
     Any of the above-mentioned plots is a green land plot. 
     Any of the above-mentioned soil is green land soil in China. 
     Any of the above-mentioned plots is a green land plot in China. 
     Any of the above-mentioned soil is urban green land soil. 
     Any of the above-mentioned plots is an urban green land plot. 
     Any of the above-mentioned soil is green land soil in the Yangtze River Delta of China. 
     Any of the above-mentioned plots is a green land plot in the Yangtze River Delta of China. 
     Any of the above-mentioned soil is urban green land soil in the Yangtze River Delta of China. 
     Any of the above-mentioned plots is an urban green land plot in the Yangtze River Delta of China. 
     Any of the above-mentioned soil is park green land soil. 
     Any of the above-mentioned plots is a park green land plot. 
     Any of the above-mentioned soil is urban park green land soil. 
     Any of the above-mentioned plots is an urban park green land plot. 
     Any of the above-mentioned soil is park green land soil in the Yangtze River Delta of China. 
     Any of the above-mentioned plots is a park green land plot in the Yangtze River Delta of China. 
     Any of the above-mentioned soil is urban park green land soil in the Yangtze River Delta of China. 
     Any of the above-mentioned plots is an urban park green land plot in the Yangtze River Delta of China. 
     The Yangtze River Delta refers to China&#39;s Shanghai, Jiangsu Province, and Zhejiang Province. 
     Any of the above-mentioned soil samples are taken from 0-20 cm surface soil. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the linear relationship between the copy number content of the target OTU and the total nitrogen content of the soil. 
     
    
    
     EMBODIMENTS 
     The following examples facilitate a better understanding of the present invention but do not limit the present invention. The experimental methods in the following examples, unless otherwise specified, are all conventional. The experimental materials used in the following examples, unless otherwise specified, are all purchased from conventional biochemical reagent stores. The quantitative experiments in the following examples are all set to repeat the experiment three times, and the results are averaged. 
     The soil quality indicators are determined according to relevant national standards, industry standards, and local standards, see Table 1 for details. 
     
       
         
           
               
             
               
                 !TABLE 1 
               
             
            
               
                   
               
               
                 Determination methods of soil quality indicators 
               
               
                 Detected  
                   
               
               
                 Indicator 
                 Determination method 
               
               
                   
               
            
           
           
               
               
            
               
                 pH 
                 LY/T 1239-1999 Determination of pH value in forest soil 
               
               
                 conductivity 
                 LY/T 1251-1999 Analysis methods of watersoluble salts  
               
               
                   
                 of forest soil (conductivity method) 
               
               
                 organic  
                 NY/T 1121.6-2006 Method for determination of soil  
               
               
                 matter  
                 organic matter  
               
               
                 total  
                 LY/T 1228-2015 Nitrogen determination methods of  
               
               
                 nitrogen  
                 forest soil (Kjeldahlmethod)  
               
               
                 available  
                 LY/T 1228-2015 Nitrogen determination methods of  
               
               
                 nitrogen  
                 forest soil (alkali-diffusion method)  
               
               
                 total  
                 LY/T 1232-2015 Phosphorus determination methods of  
               
               
                 phosphorus 
                 forest soil (alkali fusion Mo-Sb anti spectrophotometric  
               
               
                   
                 method)  
               
               
                 total  
                 LY/T 1234-2015 Potassium determination methods of  
               
               
                 potassium  
                 forest soil (alkali fusion method)  
               
               
                 available  
                 DB31/T 661-2012 Appendix F AB-DTPA extraction/ 
               
               
                 phosphorus  
                 inductively coupled plasma mass spectrometer  
               
               
                 available  
                 DB31/T 661-2012 Appendix F AB-DTPA extraction/ 
               
               
                 potassium  
                 inductively coupled plasma emission spectrometer  
               
               
                 available  
                 DB31/T 661-2012 Appendix F AB-DTPA extraction/ 
               
               
                 sulfur 
                 inductively coupled plasma mass spectrometer  
               
               
                 available  
                 Refer to Appendix E (watersaturated extraction) in DB31/ 
               
               
                 chlorine 
                 T 661-2012  
               
               
                 exchangeable  
                 Refer to Appendix E (watersaturated extraction) in DB31/ 
               
               
                 sodium  
                 T 661-2012  
               
               
                 total arsenic 
                 GB/T22105.2-2008 Soil quality-Analysis of total  
               
               
                   
                 mercury, arsenic and lead contents--Atomic fluorescence  
               
               
                   
                 spectrometry  
               
               
                 total bronze  
                 Total digestion inductively coupled plasma mass  
               
               
                   
                 spectrometer method  
               
               
                 total zinc  
                 Total digestion inductively coupled plasma mass  
               
               
                   
                 spectrometer method  
               
               
                 total lead  
                 Total digestion inductively coupled plasma mass  
               
               
                   
                 spectrometer method  
               
               
                 total  
                 Total digestion inductively coupled plasma mass  
               
               
                 chromium  
                 spectrometer method  
               
               
                 total nickel  
                 Total digestion inductively coupled plasma mass  
               
               
                   
                 spectrometer method  
               
               
                 available  
                 Refer to DB31/T 661-2012 Appendix F AB-DTPA  
               
               
                 calcium  
                 extraction/inductively coupled plasma emission  
               
               
                   
                 spectrometer  
               
               
                 available  
                 DB31/T 661-2012 Appendix F AB-DTPA  
               
               
                 manganese  
                 extraction/inductively coupled plasma emission  
               
               
                   
                 spectrometer  
               
               
                 available  
                 DB31/T 661-2012 Appendix F AB -DTPA  
               
               
                 zinc 
                 extraction/inductively coupled plasma emission  
               
               
                   
                 spectrometer  
               
               
                 total  
                 USEPA 7473-2007 Thermal decomposition of  
               
               
                 mercury  
                 atomic absorption spectrophotometry 
               
               
                   
               
               
                 Note: Compared with the reference method, the only differencein available calcium detection is that the detection target is available calcium. 
               
            
           
         
       
     
     Example 1. Discovery of OUT Related to Total Nitrogen Content in the Soil 
     1. Collection of Soil Samples 
     In November 2017, research sample plots were set up in representative parks and green lands in 16 administrative regions of Shanghai, China. 
     Sampling method: The collection of soil samples followed the principle of multi-point mixing. Eight sampling points were selected from each sample plot. The soil drill with a diameter of 2.5 cm was used to collect the 0-20 cm topsoil respectively, and then the soil sample was mixed into one soil sample. 
     The soil samples were mixed evenly and passed through a 2 mm sieve to remove plant roots, gravel, and other debris. Then each soil sample was divided into two portions. One portion was air-dried naturally, and then as the sample for the determination of soil chemical properties in step 2; the other portion was stored at −80° C., and then as the sample used for the extraction of total soil DNA in step 3. 
     2. Analysis and Determination of Soil Quality Indicators 
     In step 1, the natural air-dried soil samples were analyzed and determined for soil quality indicators. The measurement results of soil quality indicators were shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Test results of soil quality indicators 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 minimum  
                 maximal  
                 average  
               
               
                   
                 Detection Indicator 
                 value 
                 value 
                 value 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 pH 
                 5.32 
                 8.79 
                 7.92 
               
               
                   
                 conductivity(μS/cm) 
                 60.70 
                 656.52 
                 142.57 
               
               
                   
                 organic matter(g/kg) 
                 7.10 
                 46.62 
                 27.59 
               
               
                   
                 total nitrogen(g/kg) 
                 0.47 
                 2.34 
                 1.13 
               
               
                   
                 available nitrogen(mg/kg) 
                 25.85 
                 152.64 
                 84.68 
               
               
                   
                 total phosphorus(g/kg) 
                 0.42 
                 1.00 
                 0.68 
               
               
                   
                 total potassium(g/kg) 
                 15.80 
                 25.43 
                 19.08 
               
               
                   
                 available phosphorus(mg/kg) 
                 0.85 
                 48.20 
                 8.66 
               
               
                   
                 available potassium(mg/kg) 
                 28.20 
                 397.89 
                 188.90 
               
               
                   
                 available sulfur(mg/kg) 
                 13.06 
                 96.65 
                 52.36 
               
               
                   
                 available chlorine(mg/L) 
                 4.16 
                 1900.00 
                 41.46 
               
               
                   
                 exchangeable sodium(mg/L) 
                 3.30 
                 993.00 
                 21.60 
               
               
                   
                 total arsenic(mg/kg) 
                 4.81 
                 13.50 
                 8.73 
               
               
                   
                 total bronze(mg/kg) 
                 16.38 
                 99.84 
                 36.05 
               
               
                   
                 total zinc(mg/kg) 
                 87.38 
                 223.87 
                 125.52 
               
               
                   
                 total lead(mg/kg) 
                 18.24 
                 52.18 
                 29.01 
               
               
                   
                 total chromium(mg/kg) 
                 55.40 
                 101.00 
                 72.90 
               
               
                   
                 total nickel(mg/kg) 
                 27.40 
                 44.59 
                 36.62 
               
               
                   
                 available calcium(mg/kg) 
                 198.36 
                 366.95 
                 282.89 
               
               
                   
                 available manganese(mg/kg) 
                 8.55 
                 29.46 
                 16.76 
               
               
                   
                 available zinc(mg/kg) 
                 1.81 
                 29.58 
                 9.05 
               
               
                   
                 total mercury(mg/kg) 
                 0.05 
                 0.57 
                 0.21 
               
               
                   
                   
               
            
           
         
       
     
     3. Diversity Analysis of Soil Archaea Population 
     (1). Extraction of Total DNA from Soil Samples Stored at −80° C. in Step 1. 
     Total DNA of soil samples was extracted with MoBioPowerSoil® DNA Isolation Kit (MoBio Laboratories, Carlsbad, Inc., CA, USA). Each soil sample was extracted twice repeatedly, and the total DNA extracted twice was mixed to obtain a DNA sample. For 76 soil samples, corresponding 76 DNA samples were obtained. All DNA samples were stored at −80° C. 
     The DNA quality was examined by Nanodrop 2000 ultra-micro spectrophotometer and 0.8% agarose gel electrophoresis (5V cm −1 , 45 min). The OD260/OD280 of the 76 DNA samples were in the range of 1.8-2.0, the maximum value of OD260/OD280 was 1.98, and the minimum value of OD260/OD280 was 1.81. 
     (2). Archaea 16S rRNA Gene Amplification and High-Throughput Sequencing 
     The DNA sample was used as a template, and a primer pair composed of primer 524F-10-ext and primer Arch958R-mod was used for PCR amplification. After PCR amplification was completed, the PCR products were subjected to 2% agarose gel electrophoresis, and then the target bands were cut and purified by the GeneJET Gel Recovery Kit (Thermo Scientific), and then the sequencing library was constructed, and the Illumina MiSeq sequencing platform (Illumina, San Diego, Calif., USA) was used for sequencing. 
     Primer 524F-10-ext and primer Arch958R-mod are universal primers for archaea, and the target sequence is located in the V4-V5 variable region of the archaea 16S rRNA gene. 
     
       
         
           
               
            
               
                 524F-10-ext (SEQ ID NO. 4 of sequence listing): 
               
               
                 5′-TGYCAGCCGCCGCGGTAA-3′; 
               
               
                   
               
               
                 Arch958R-mod (SEQ ID NO. 5 of sequence listing): 
               
               
                 5′YCCGGCGTTGAVTCCAATT-3′; 
               
            
           
         
       
     
     Y stands for C or T; V stands for G, A or C. 
     The reaction system for PCR amplification was 30 μL. The active ingredients were 15 μL of Phusion® High-Fidelity PCR Master Mix (New England Biolabs), primers, and template DNA. In the reaction system, the concentration of primer 524F-10-ext and primer Arch958R-mod were both 0.2 μM. In the reaction system, the content of template DNA was 10 ng. 
     The PCR amplification reaction program: 95° C. pre-denaturation 3 min; 95° C. denaturation 30 s, 55° C. annealing 30 s, 72° C. extension 45 s, 33 cycles; 72° C. extension 5 min. 
     (3). High-Throughput Data Analysis and Results 
     The specific steps for bioinformatics analysis of high-throughput sequencing results were as follows: 1) Extracted the same sample sequence from the original data according to the sample-specific label to form a separate file, and removed the label and primer sequences; 2) FLASH (V1.2.7) software was used for sequence splicing; 3) Qiime (V1.7.0) software was used to perform quality filtering on the original sequence after sequencing; 4) UCHIME software was used to detect chimeras and deleted them; 5) Uparse (v7.0.1001) software was used to divide Operational Taxonomic Units (OTUs) at a similarity level of 95%; 6) Since the reliability of the single-copy sequence was questioned, the single-copy sequence was removed in the subsequent analysis; 7) In order to remove the influence of different sequencing depths between samples, the sample OTU table was homogenized to the same sequencing depth; 8) Aligned the sequence of OTUs based on the RDP database and determined the taxonomic status thereof. 
     Total 27765 archaea 16S rRNA gene sequences were selected from each sample for subsequent analysis. The archaea 16S rRNA gene sequences were classified at 95% sequence similarity, and a total of 580 OTUs were obtained. 
     4. Correlation Analysis Between Soil Archaea Groups and Soil Quality Indicators 
     Performed Pearson correlation analysis on the 580 OTUs obtained in step 3 and the soil chemical indicators data obtained in step 2. 
     The results show that among 580 OTUs, the abundance of archaeal OTU300 in the soil has the strongest correlation with the total nitrogen content in the soil; the correlation between the abundance of archaea OTU69 in the soil and the total nitrogen content of the soil comes second; meanwhile, the abundance of archaea OTU300 in the soil was significantly positively correlated with the total nitrogen content of the soil, with a correlation coefficient r of 0.486; the correlation coefficient between the abundance of archaea OTU69 in the soil and the total nitrogen content of the soil was −0.293. The abundance of archaea OTU300 or archaea OTU69 in the soil can be used to reflect the total nitrogen content of the soil. 
     Example 2: Establishing a Linear Relationship Between OTU and Soil Chemical Characteristics 
     1. Archaea Marker Gene Probe Design 
     According to the sequencing results, a probe for detecting OTU300 was designed. 
     
       
         
           
               
               
            
               
                   
                 Probe300-1 probe (SEQ ID NO. 6 of sequence 
               
               
                   
                 listing): 
               
               
                   
                 5′-AGGATACTACAGAGCTAGGA-3′. 
               
               
                   
                   
               
               
                   
                 Probe300-2 probe (SEQ ID NO. 1 of sequence 
               
               
                   
                 listing): 
               
               
                   
                 5′-TTGGCTTCGCGCTAACCCAGT-3′. 
               
            
           
         
       
     
     The Probe300-1 was a Taqman probe with a fluorescent group FAM at its 5′end and a fluorescence quenching group TAMRA at its 3′end. Probe300-2 was a Taqman probe with a fluorescent group FAM at its 5′end and a fluorescence quenching group TAMRA at its 3′end. 
     According to the sequencing results, a probe for detecting OTU69 was designed. 
     
       
         
           
               
               
            
               
                   
                 Probe69-1 probe (SEQ ID NO. 7 of sequence 
               
               
                   
                 listing): 
               
               
                   
                 5′-ACCCGCTCAACGGTTGGGCT-3′. 
               
               
                   
                   
               
               
                   
                 Probe69-2 probe (SEQ ID NO. 8 of sequence 
               
               
                   
                 listing): 
               
               
                   
                 5′-TGATGGGATGGCCTCGAGCT-3′. 
               
            
           
         
       
     
     Probe69-1 was a Taqman probe with a fluorescent group FAM at its 5′end and a fluorescence quenching group TAMRA at its 3′end. Probe69-2 was a Taqman probe with a fluorescent group FAM at its 5′end and a fluorescence quenching group TAMRA at its 3′end. 
     2. Determination of the Copy Number of Archaea Marker Gene in Soil 
     According to the measured value, soil samples with a gradient distribution of total nitrogen content were randomly selected from the soil samples in step 1 of Example 1. 
     (1) Took soil samples for extraction of the total DNA. 
     The extraction method of the total DNA was the same as the (1) of step 3 of Example 1. 
     (2) Took the template solution (that was, the total DNA solution obtained in step (1)), and performed fluorescent quantitative PCR (probe method) on the LightCycler® 96 real-time fluorescent quantitative PCR instrument. 
     A primer pair consisting of the primer 524F-10-ext and the primer Arch958R-mod was used. A Probe300-1 probe or Probe300-2 probe or Probe69-1 probe or Probe69-2 probe was used. 
     Reaction system (20 μL): 10 μL Premix Ex Taq (Takara, Dalian, China), 0.4 μL primer 524F-10-ext, 0.4 μL primer Arch958R-mod, 0.2 μL probe, 2 μL template solution and 7 μL sterile water. In the reaction system, the concentration of primer 524F-10-ext was 0.2 μM, the concentration of primer Arch958R-mod was 0.2 μM, and the concentration of probe was 0.1 μM. In the reaction system, the content of template DNA was 7 ng. 
     Reaction program: 95° C. pre-denaturation for 120 s; 95° C. denaturation for 10 s, 60° C. annealing extension for 45 s, 45 cycles. 
     The specificity of amplification was determined by the melting curve. 
     The Ct value was substituted into the standard curve equation to obtain the copy number of the target OTU, and then the copy number content (unit was copy number/g, that was, the copy number of the target OTU in each gram of the dry soil sample) of the target OTU in the soil sample was calculated. 
     The preparation method of the standard curve equation was shown in step (3). 
     (3) Constructed a standard curve for real-time PCR 
     Ligated the DNA molecule (amplified from total soil DNA) shown as SEQ ID NO. 2 of the sequence listing to the pMD18-T vector to obtain OTU300 standard plasmid. Using TE buffer as the solvent, prepared the standard plasmid solutions containing different concentrations of OTU300 standard plasmid (the DNA concentration in the standard plasmid solution was measured by Nanodrop 2000 ultra-micro spectrophotometer, and was converted into DNA copy number, which was the OTU300 copy number). Each standard plasmid solution was used as a template solution, and detection was performed according to the method of step (2) (using Probe300-1 probe or Probe300-2 probe) to obtain the standard curve equation with the logarithm of OTU300 copy number (logarithm with base 10) as the independent variable and Ct as the dependent variable. 
     
       
         
           
               
            
               
                 SEQ ID NO. 2: 
               
               
                 TGTCAGCCGCCGCGGTAATACCAGCACCCCGAGTGGTCGGGACGATT 
               
               
                   
               
               
                 ATTGGGCCTAAAGCATCCGTAGCCGGTTCTGCAAGTCTCCCGTTAAA 
               
               
                   
               
               
                 TCCAACTGCTCAACAGGTGGGCTGCGG AGGATACTACAGAGCTAG   
               
               
                   
               
               
                   GA GGCAGGAGAGGCAAGCGGTACTCAGTGGGTAGGGGTAAAATCCG 
               
               
                   
               
               
                 TTGATCCATTGAAGACCACCAGTGGCGAAGGCGGCTTGCCAGAATG 
               
               
                   
               
               
                 CGCTCGACGGTGAGGGATGAAAGCTGGGGGAGCAAACCGGATTAGA 
               
               
                   
               
               
                 TACCCGGGTAGTCCCAGCCGTAAACGATGCAGACTCGGTGATGGG TT   
               
               
                   
               
               
                   GGCTTCGCGCTAACCCAGT GCCGCAGGGAAGCCGTTAAGTCTGCCGC 
               
               
                   
               
               
                 CTGGGTAGTACGGTCGCAAGACTGAAACTTAAAGGAATTGGCGGGG 
               
               
                   
               
               
                 GAGCACCACAAGGGGTGAAGCCTGCGGTTCAATTGGATTCAACGCC 
               
               
                   
               
               
                 GGA 
               
            
           
         
       
     
     Ligated the DNA molecule (amplified from total soil DNA) shown as SEQ ID NO. 3 of the sequence listing to the pMD18-T vector to obtain OTU69 standard plasmid. Using TE buffer as the solvent, prepared the standard plasmid solutions containing different concentrations of OTU69 standard plasmid (the DNA concentration in the standard plasmid solution was measured by Nanodrop 2000 ultra-micro spectrophotometer, and was converted into DNA copy number, which was the OTU69 copy number). Each standard plasmid solution was used as a template solution, and detection was performed according to the method of step (2) (using Probe69-1 probe or Probe69-2 probe) to obtain the standard curve equation with the logarithm of OTU69 copy number (logarithm with base 10) as the independent variable and Ct as the dependent variable. 
     
       
         
           
               
            
               
                 SEQ ID NO. 3: 
               
               
                 TGTCAGCCGCCGCGGTAATACCAGCACCCCGAGTGGTCGGGACGATT 
               
               
                   
               
               
                 ATTGGGCCTAAAGCATCCGTAGCCGGTCATGCAAGTCTTCCGTTAAA 
               
               
                   
               
               
                 TCC ACCCGCTCAACGGTTGGGCT GCGGAGGATACTACGTGGCTAG 
               
               
                   
               
               
                 GAGGCGGGAGAGGCAAGCGGTACTCAGTGGGTAGGGGTAAAATCCT 
               
               
                   
               
               
                 TTGATCCATTGAAGACCACCAGTGGCGAAGGCGGCTTGCCAGAACG 
               
               
                   
               
               
                 CGCTCGACGGTGAGGGATGAAAGCTGGGGGAGCAAACCGGATTAGA 
               
               
                   
               
               
                 TACCCGGGTAGTCCCAGCTGTAAACGATGCAGACTCGG TGATGGGAT   
               
               
                   
               
               
                   GGCCTCGAGCT ATCCCAGTGCCGCAGGGAAGCCGTTAAGTCTGCCGC 
               
               
                   
               
               
                 CTGGGGAGTACGGTCGCAAGACTGAAACTTAAAGGAATTGGCGGGG 
               
               
                   
               
               
                 GAGCACCACAAGGGGTGAAGCCTGCGGTTCAATTGGATTCAACGCC 
               
               
                   
               
               
                 GGA 
               
            
           
         
       
     
     The efficiency of fluorescence quantitative PCR amplification was between 90% and 110%. 
     3. Establishment of a Linear Relationship Between Copy Number of Archaea Marker Gene and Chemical Characteristics of the Soil 
     The results of the measured total nitrogen values (unit: g/kg), Ct values, and target OTU copy number content (unit: copy number/g) of the soil samples were shown in Table 3. The measured values of total nitrogen of the soil samples were the data obtained in step 2 of Example 1. The Ct values and the copy number content of the target OTU of the soil samples were the data obtained in step 2 of the present embodiment. A Probe300-2 probe was used to perform fluorescence quantitative PCR, the relative abundance of target OTU of the soil (reflected as the copy number of target OTU in the soil) had a good linear relationship with the total nitrogen content of the soil. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                   
                 The 
                   
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 measured 
                   
                   
                   
                   
               
               
                 Soil 
                 value of 
                 Probe300-1 
                 Probe300-2 
                 Probe69-1 
                 Probe69-2 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 sample 
                 total 
                   
                 copy number 
                   
                 copy number 
                   
                 copy number 
                   
                 copy number 
               
               
                 number 
                 nitrogen 
                 Ct value 
                 content 
                 Ct value 
                 content 
                 Ct value 
                 content 
                 Ct value 
                 content 
               
               
                   
               
               
                 1 
                 2.34 
                 20.59 
                 2.5 × 10 7   
                 18.19 
                 5.0 × 10 7   
                 21.42 
                 1.3 × 10 7   
                 18.96 
                 1.4 × 10 7   
               
               
                 2 
                 1.94 
                 21.71 
                 1.2 × 10 7   
                 18.80 
                 3.3 × 10 7   
                 21.24 
                 1.4 × 10 7   
                 19.06 
                 1.4 × 10 7   
               
               
                 3 
                 1.46 
                 22.49 
                 7.4 × 10 6   
                 20.20 
                 1.4 × 10 7   
                 21.80 
                 9.8 × 10 6   
                 19.48 
                 1.0 × 10 7   
               
               
                 4 
                 1.15 
                 23.60 
                 3.6 × 10 6   
                 21.24 
                 6.9 × 10 6   
                 21.53 
                 1.2 × 10 7   
                 19.16 
                 1.3 × 10 7   
               
               
                 5 
                 0.93 
                 23.63 
                 3.5 × 10 6   
                 21.02 
                 8.0 × 10 6   
                 21.41 
                 1.3 × 10 7   
                 19.44 
                 1.0 × 10 7   
               
               
                 6 
                 0.62 
                 23.02 
                 5.3 × 10 6   
                 22.19 
                 3.7 × 10 6   
                 21.20 
                 1.4 × 10 7   
                 18.49 
                 2.0 × 10 7   
               
               
                 7 
                 0.47 
                 24.20 
                 2.5 × 10 6   
                 26.08 
                 0.3 × 10 6   
                 20.54 
                 2.2 × 10 7   
                 18.31 
                 2.3 × 10 7   
               
            
           
           
               
               
               
               
               
            
               
                 Linear equation 
                 y = 0.0745x + 0.6330 
                 y = 0.0361x + 0.6785 
                 y = −0.8773x + 2.4962 
                 y = −0.6935x + 2.3074 
               
               
                 R 2   
                 0.7867 
                 0.9151 
                 0.2695 
                 0.2651 
               
               
                   
               
            
           
         
       
     
     Note: soil sample 1, collected from a green land of the park in Fengxian District; soil sample 2, collected from a green land of the park in Huangpu District; soil sample 3, collected from a green land of the park in Hongkou District; soil sample 4, collected from a green land of the park in Songjiang District; soil sample 5, collected from a green land of the park in Qingpu District; soil sample 6, collected from a green land of the park in Xuhui District; soil sample 7, collected from a green land of the park in Baoshan District. 
     A Probe300-2 probe was used to perform fluorescence quantitative PCR, the linear relationship between the copy number content of the target OTU in the soil and the total nitrogen content of the soil as shown in  FIG. 1 . The linear equation is y=0.0361x+0.6785; R 2 =0.9151; y represents the total nitrogen content (g/kg), and x represents the copy number content of the target OUT (×10 6  copies/g). 
     Example 3. Molecular Detection of the Total Nitrogen Content of the Soil Samples of Unknown Urban Green Lands 
     Randomly selected three green lands in Shanghai Botanical Garden, Nanjing Xuanwu Lake Park, and Suzhou Wujiang Park in China. 
     Sampling method: The collection of soil samples followed the principle of multi-point mixing: Eight sampling points were selected from each sample plot. The soil drill with a diameter of 2.5 cm was used to collect the 0-20 cm topsoil respectively, and then the soil sample was mixed into one soil sample. 
     The soil samples were mixed evenly and passed through a 2 mm sieve to remove plant roots, gravel, and other debris. Then each soil sample was divided into two portions. One portion was air-dried naturally, and then as a sample to be detected to get the actual measured value of the total nitrogen content (unit: mg/kg). The other part was stored at −80° C. and then as a sample for extraction of total soil DNA. 
     1. Extraction of total DNA of soil samples. Adopted MoBioPowerSoil® DNA Isolation Kit (MoBio Laboratories, Carlsbad, Inc., CA, USA). Extracted each soil sample two times and mixed all of the extracted total DNA to get a DNA sample. 
     2. Took the template solution (i.e., the DNA sample obtained in step 1), and performed fluorescent quantitative PCR (probe method) on the LightCycler® 96 real-time fluorescent quantitative PCR instrument. Reaction system (20 μL): 10 μL Premix Ex Taq (Takara, Dalian, China), 0.4 μL primer 524F-10-ext, 0.4 μL primer Arch958R-mod, 0.2 μL Probe300-2 probe, 2 μL template solution, and 7 μL sterile water. In the reaction system, the concentration of primer 524F-10-ext was 0.2 μM, the concentration of primer Arch958R-mod was 0.4M, and the concentration of Probe300-2 probe was 0.1 μM. In the reaction system, the content of template DNA was 7 ng. 
     Reaction program: 95° C. pre-denaturation for 120 s; 95° C. denaturation for 10 s, 60° C. annealing extension for 45 s, 45 cycles. 
     The Ct value was substituted into the standard curve equation to obtain the copy number of OTU300, and then the copy number content of OTU300 of the soil sample was calculated (the unit was copy number/g, that was, the number of copies of OTU300 per gram of dry weight of soil sample). 
     The construction method of the standard curve equation was shown in step (3) of part 2 of Example 2. 
     3. The copy number content of OTU300 of the soil sample was substituted into the linear equation to obtain the calculated value of the total nitrogen content of the soil sample (unit: g/kg). 
     The linear equation is: y=0.0361x+0.6785; R2=0.9151; wherein y represents the total nitrogen content (g/kg), x represents the copy number content of OTU300 (×106 copies/g). 
     The results of the copy number content of OTU300 in the soil sample (unit: copy number/g), the calculated value of the total nitrogen content of the soil sample (unit: g/kg), and the measured value of the total nitrogen content of the soil sample (unit: g/kg) are shown in Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                   
                 The  
                 The  
               
               
                   
                   
                   
                 calculated 
                 measured 
               
               
                   
                   
                 Thecopy  
                 value of  
                 value of  
               
               
                   
                   
                 number 
                 the 
                 the  
               
               
                   
                   
                 content of 
                 total  
                 total 
               
               
                   
                   
                 OTU300 
                 nitrogen 
                 nitrogen  
               
               
                   
                   
                 (copy  
                 content 
                 content 
               
               
                   
                   
                 number/g) 
                 (g/kg) 
                 (g/kg) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Sample 1 
                 6.8 × 10 6   
                 0.92 
                 0.78 
               
               
                   
                 Shanghai 
                   
                   
                   
               
               
                   
                 Botanical Garden 
                   
                   
                   
               
               
                   
                 Sample 2 
                 4.1 × 10 6   
                 0.83 
                 0.71 
               
               
                   
                 Shanghai 
                   
                   
                   
               
               
                   
                 Botanical Garden 
                   
                   
                   
               
               
                   
                 Sample 3 
                 5.9 × 10 6   
                 0.89 
                 0.75 
               
               
                   
                 Shanghai 
                   
                   
                   
               
               
                   
                 Botanical Garden 
                   
                   
                   
               
               
                   
                 Sample 4 
                 1.2 × 10 7   
                 1.12 
                 1.38 
               
               
                   
                 Nanjing Xuanwu 
                   
                   
                   
               
               
                   
                 Lake Park 
                   
                   
                   
               
               
                   
                 Sample 5 
                 1.3 × 10 6   
                 0.73 
                 0.61 
               
               
                   
                 Nanjing Xuanwu 
                   
                   
                   
               
               
                   
                 Lake Park 
                   
                   
                   
               
               
                   
                 Sample 6 
                 6.8 × 10 6   
                 0.92 
                 0.78 
               
               
                   
                 Nanjing Xuanwu 
                   
                   
                   
               
               
                   
                 Lake Park 
                   
                   
                   
               
               
                   
                 Sample 7 
                 2.6 × 10 5   
                 0.69 
                 0.47 
               
               
                   
                 Suzhou Wujiang 
                   
                   
                   
               
               
                   
                 Park 
                   
                   
                   
               
               
                   
                 Sample 8 
                 8.8 × 10 6   
                 1.00 
                 1.33 
               
               
                   
                 Suzhou Wujiang 
                   
                   
                   
               
               
                   
                 Park 
                   
                   
                   
               
               
                   
                 Sample 9 
                 1.6 × 10 6   
                 0.74 
                 0.64 
               
               
                   
                 Suzhou Wujiang 
                   
                   
                   
               
               
                   
                 Park 
               
               
                   
                   
               
            
           
         
       
     
     INDUSTRIAL APPLICATION 
     The invention discloses a method for detecting the total nitrogen content of the soil or comparing the total nitrogen content of the soil between different plots, which has the following advantages: detecting the total nitrogen content of the soil or comparing the total nitrogen content of the soil between different plots, and small sample demand, no need for pre-treatment, short required time, low labor cost, realizing the rapid automatic detection of large quantities of samples. The present invention deserves to apply and promote in the evaluation of soil samples.