| Nitrification was generally existed in soil and influenced by many factors, such as pH, temperature, soil moisture and the contents of ammonium, soil pH was one of the most important factors. Early research had shown that:Nitrification was widely existed in neutral and calcareous soil and had strong ammonia oxidation activity, but the existence of nitrification in acid soil was almost undetectable. Along with the continuously study of nitrification, many researchers have proved the existent of nitrification in acid soil. Nitrifications in some acid soil were even more strongly than in alkaline soil. With the development of molecular research technology, the intensity of soil nitrification and its influencing factors have received highly attentions. Microbial mechanism of soil nitrification process become a hot research topic.Soil pH significantly affected the process of nitrification. Firstly, nitrifiers have grown slowly under the condition of low soil pH and even undetectable. Secondly, soil pH significantly influences the content of nitrification substrates. Nitrification substrates is ammonia, but ammonia and ammonium in soil are in a dynamic equilibrium. Soil pH is one of the most important conditions influencing the dynamic equilibrium. Under the condition of low soil pH, ammonia tends to be transformed into ammonium, while the opposite happened under the condition of high soil pH. Thirdly, soil pH affects the activity of nitrifiers as well as nitrification.Our experiments chose acid yellow soil (pH=4.2) and purple soil (pH=7.0) in Chongqing jinyun mountain, acid paddy soil (pH=5.6) and calcareous paddy soil (pH= 8.2). calcareous paddy soil collected from Guanlong Village, Chongqing, and acid paddy soil collected from long-term positioning plots in the Southwest University.Yellow soil and purple soil both have three treatments:13C labeled treatment,12C control and13C+C2H2processing. Soil samples cultivated56days in incubator at28℃, Samples are collected after0,28,56days cultivation. Analysis soil pH, ammonium nitrogen and nitrate nitrogen by inorganic method. We can analyze the abundance of amoA functional genes in ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) by quantitative PCR. We also can determine the community structure of AOB and AOA by using clone method. Results are as follows:After the cultivation of eight weeks, the content of nitrate nitrogen in purple soil increased from1.9mg/kg to54.5,1.6,54.8mg/kg among12C control,13C+C2H2treatment and13C labeled treatment. The corresponding content of ammonium nitrogen were75.4,249.9,102.8mg/kg. The content of ammonium nitrogen of13C treatment and12C control, were significantly reduced when compared with13C+C2H2treatment. But in yellow soil the content of ammonium nitrogen were0.8,0.9,0.6mg/kg, compared with0.6mg/kg in the beginning of cultivation, did not increased obviously. This phenomenon also happened in the content of ammonium nitrogen, were411.4,468.4,378.5mg/kg. Nitrification significantly occurred in purple soil, but hardly observed in yellow soil.After cultivation, the copy number of amoA functional genes of AOB in purple soil using I2C control and13C labeled treatment, were respectively increased from1.48x107to1.08×108and1.13×108, while13C+C2H2treatment was1.88E+07hadno obvious changes. After cultivation,12C control,13C+C2H2and13C labeled treatments reduced from8.23×107to1.73x107,3.56x107and1.96×107, respectively. In yellow soil, after cultivation, the copy number of amoA functional genes in AOA were3.05x106,1.60×107,3.23×106, significantly reduced, respectively. The copy numbers of amoA functional genes in AOB were3.09×107,1.77x107,1.30×107, respectively. There is no obvious changes. Before cultivation, the copy number of amoA functional genes in AOA and AOB in the purple soil were higher than those in yellow soil.Both acid paddy soil and calcareous paddy soil have two treatments:13C labeled and12C controlled treatments. Results are as follows:After the cultivation of eight weeks, In calcareous paddy soil, the content of nitrate nitrogen in12C controlled and13C labeled processing increased from0.9mg/kg to215.4 and205.4mg/kg. The content of ammonium nitrogen decreased from800mg/kg to13.9and52.0mg/kg respectively. In acid paddy soil, the content of nitrate nitrogen was10.8and9.4mg/kg, compared with17.8mg/kg in cultivation starting, there is no obvious increase. The content of ammonium nitrogen decreased to561and556mg/kg. Results show that nitrification happened obviously in calcareous paddy soil and acid paddy soil.After cultivation, in calcareous paddy soil by12C and13C treatments, their copy number of amoA functional genes in AOB increased from9.99×107to6.68x108and8.67x108, respectively. And copy number of amoA functional genes in AOA was not obviously changed compared with cultivation starting. In acid paddy soil, treatments by12C and13C, their copy number of amoA functional genes in AOA increased from9.58×106to2.98×108and1.35×108, respectively. While the copy number of amoA functional genes in AOB was not obviously different compared with cultivation starting. The copy numbers of amoA functional genes in AOA and AOB in calcareous paddy soil were higher than in acid paddy soil.This study describes the effects of soil pH on nitrification and ammonia-oxidizing microorganisms as well as the main promoter of nitrification in the purple soil and paddy soil. Conclusions are as follows:(1) soil pH has a significantly influence on nitrification, especially between4.2and8.2, higher soil pH goes along wiith the stronger nitrification.(2) Soil pH also have a significant impact on species of ammonia oxidation microorganisms. In neutral and calcareous soil, AOB plays a dominated effect in the number of ammonia oxidation,but AOAin acid soils.(3) Soil pH have significantly affects on the activity of nitrifiers.(4) AOB, as the promoter of nitrification in purple soil and calcareous paddy soil were100%belong to group of Nitrosospira Cluster3. The main group of AOB in Acid paddy soil is Nitrosomonas Cluster. In acid paddy soil, the main group of AOA is Group1.1b. In calcareous paddy soil, the group of AOA belongs to the Group of1.1a. The main group of AOA16S rRNA genes observed in Calcareous and acid paddy soil are Group1.1a and Group1.1b, respectively... |
PDF Full Text Request