Study On Soil Microbial Abundance In Dry Loess Plateau Farmland Based On Real-time Quantitative PCR

The Loess Plateau is large,accounting for more than one-seventh of the country's arable land.It is the main grain producing area in northwest China.However,the lack of resources,fragile ecological environment and generally low fertility limit the increase of wheat yield.At present,although many scholars have done a lot of research on the farmland of the Loess Plateau,most of them have focused on the study of soil moisture,carbon,nitrogen and phosphorus nutrient sink and yield,while the use of molecular biological means to study its functional microorganisms is relatively rare.Based on the above discussion,this research took the long-term positioning test of the agricultural ecology test station of the changwu loess plateau as the platform,and conducted a study on the soil microbial characteristics of the farmland of the loess plateau through real-time PCR technology.In this paper,a total of 28 representative fertilization systems were selected,It has been roughly divided into three categories,1.Different P gradients(6treatments,N12?N12P6?N12P12?N12P18?N12P24?N12P12K12).2.N.P gradient:high N level,N.P gradient(6treatments,CK1?P12?P24?N24?N24P12?N24P24);Medium N level,N.P gradient(6,N6P6?N6P12?N6P18?N18P6?N18P12?N18P18).3.C.N.P mix(10treatments,CKB?CK2?CKc?N16?P8?M?N16M?P8M?N16P8?N16P8M).the physicochemical properties and microbial abundance were determined,and the relationship between soil microbial abundance and environmental factors was analyzed.The following are the main conclusions of this research:(1)Long-term fertilization treatment significantly increased soil TOC,TN,microbial carbon content,and significantly reduced pH,creating an appropriate environment for the survival of bacteria.Bacteria were positively correlated with soil TOC,soil TN and soil mineralized nitrogen,and negatively correlated with soil pH.The content of ammonium nitrogen,nitrate nitrogen and respiration rate of soil showed strong promoting effect when nitrogen fertilizer was added.Soil AOB is positively correlated with soil ammonium nitrogen and nitrate nitrogen.(2)Long-term fertilization increased the abundance of soil bacteria and archaea except for the single carbon addition.C,N addition treatment and C,P addition treatment and C,N,P addition treatment to the bacteria and archaea increased the most significant trend.The number of bacteria and archaea increased by 21%and 32%,respectively,compared with CK.The number of bacteria and archaea increased by 37%and 36%respectively.The chemical fertilizer combined with organic fertilizer significantly increased the abundance of soil bacteria and archaea.(3)AOA may be the main component of archaea community in farmland soil of the loess plateau.The abundance of AOA was much higher than that of AOB without adding fertilizer or adding low-nitrogen treatment.However,AOB showed a higher response to the addition of fertilizer,especially nitrogen fertilizer.The abundance of AOB was positively correlated with ammonium and nitrate nitrogen.AOA/AOB of wheat field(CK2)without any fertilizer treatment was 3.25,while AOA/AOB of wheat field(N16)with N fertilizer treatment alone was as low as 0.48.The abundance of AOB was higher than that of AOA under high nitrogen addition.(4)The abundance of nirS cd was 109 copies per gram in the farmland soil of the Loess Plateau.The single carbon addition on the abundance of nirS cd in the soil was weak,but the combination of C,N,P addition treatment promoted the abundance of nirS cd in the soil.Long-term addition of both organic and inorganic fertilizers significantly promoted the abundance of nirS cd in the farmland soil of the Loess Plateau.Both nifH and pmoA are particularly sensitive to the addition of low concentration P,and the effect of high concentration P on them is not significant.(5)After the farming land abandoned,openness of farmland ecosystem change to a closed or semi-closed material circulation of farmland ecosystem,a great deal of the residue in the farmland branch leaves or roots secretion to once again return to ecological system,and with the vegetation succession process,microbial activity gradually enhanced,microbial biomass increased slowly.In the study,we found that the pH,water content,nifH,nirS cd and pmoA in the abandoned soil were all significantly higher than that in the cultivated soil.Cultivating methods have a significant impact on soil properties and microbial communities.