Nitrification And The Response Of Nitrifying Microorganisms To Substrates In Two Purple Soils In Southwest China

Nitrification is an important part of soil nitrogen cycle,not only connected with the nitrogen fixation and denitrification,affecting the effective utilization of plant nitrogen,soil acidification,greenhouse gas Nitrous Oxide nitrate and lead to excessive fertilization and leaching caused by water and air pollution?N₂O?is directly related to the discharge of a series of ecological environment the problem.Nitrification is also an important part of soil biochemical processes,including ammonia oxidation and nitrite oxidation.Ammonia oxidation is the first step and the speed limiting step of nitrification.Over the years,effects on soil nitrification factor has been extensively studied,including:pH,moisture,temperature,soil type and soil ammonia nitrogen content,the content of ammonia nitrogen in the substrate is a direct source to provide substrate for nitrification,starting from the factors which affect the nitrification substrates,in-depth study of its the mechanism for further solving the current fertilizer utilization rate is low and has the reference significance of this situation.Purple soil is one of the special soil types in China's soil science.It is mainly distributed in subtropical regions of China,and plays an important role in agricultural production in China.Purple soil is divided into calcareous purple soil,neutral purple soil and acid purple soil according to the content of pH and carbonate.Ammonia nitrogen is an important factor affecting nitrification,and is also an important factor affecting the abundance and community structure of nitrifying microorganisms.After 28 d incubation,the soil samples treated with three different nitrogen sources all showed the accumulation of nitrate nitrogen.At the beginning of 0 d,the accumulation of nitrate nitrogen in urea treatment was the most,and ammonia sulfate was the second treatment.The nitration of ammonia chloride was significantly lower than that of the former two,but it also showed a linear increasing trend.The accumulation of nitrate nitrogen increased from 7.77 mg N kg^-11 at 0 d to101.34 mg N kg^-11 at 28 d.The soil ammonia nitrogen content of soil under the treatment of three different nitrogen sources showed a downward trend.Ammonia nitrogen content in urea and ammonia sulfate decreased significantly in the first 14 d of incubation,from 93.98 mg N kg^-11 and94.95 mg N kg^-11 to 2.92 mg N kg^-11 and 10.50 mg kg^-11 respectively.Compared with the change of ammonia nitrogen content in the former two,ammonia nitrogen content in ammonia chloride also showed a linear decreasing trend with the incubation process,and decreased from 95.86 mg N kg^-11 at0 d to 5.32 mg N kg^-11 at 28 d.The trend of reducing soil ammonia nitrogen content by three nitrogen sources was in accordance with the accumulation trend of soil nitrate nitrogen content.In the long fallow soil and tillage soil nitrogen test,without adding nitrogen source of long-term fallow soil?F?and adding nitrogen in long-term fallow soil?F N?treatment,the nitrate content in the process of the whole incubation showed growth trend,from 0 d 5.98 and 6.44 mg N kg^-11 growth 28d 26.24 and 32.74 mg N kg^-1.Nitrate nitrogen content in cultivated soil?T?and nitrogen fertilizer T?N N?treatments also showed an increasing trend in the whole incubation process.The growth rate of nitrate nitrogen increased from 0 d to 11.94 and 11.68 mg N kg^-11 to 34.15 and 105.71 mg N mg of28 d.28,in D incubation,nitrate nitrogen content increased significantly when compared with that of F N treatment.The accumulation of nitrate nitrogen was 50.79 mg N kg kg at 28 d?F+5%T?N,which was about 1.55 times of that of F+5%T N treatment.?F+5%T?nitrification was significantly enhanced compared with?F?treatment.From the change of soil NO₃^--N,NH₄⁺-content of N can know the soil nitrification intensity of calcareous purple soil under three different nitrogen sources were simulated by one or zero order kinetics,the kinetic parameters of the simulation results show that by adding ammonia sulfate and urea as the nitrogen source of the soil,the nitrification kinetics were accorded with the first-order kinetics the model?R²=0.989 and 0.992?.The nitrification potential Np of ammonia sulfate and urea treatments was 131+10.9 mg N kg^-11 and 131+6.9 mg N kg^-1,respectively.The rate of nitrification rate,K and nitrification rate of urea treated soil were higher than those of ammonia sulfate treatment.The nitrification kinetics of soil treated with ammonia chloride was in accordance with the zero order kinetic model?R²>0.99?.The long-term fallow soil plus 5%tillage fertilization soil net nitrification rate after that?T N?with 28 d incubation in the process of net nitrification rate was 3.35 mg N kg^-11 d^-1?F N?was significantly higher than that of treatment,?F+5%T?N?F N?was significantly higher than that of treatment,but significantly lower than that of T?N?processing,obtained by the net nitrification rate of soil nitrification,?F+5%T?N treatment compared to long-term fallow soil increased significantly.In the four treatments,the copy number of AOB amoA gene in calcareous purple soil showed a significant change trend in incubation.Except for ammonia chloride treatment,AOB abundance in Control,ammonia sulfate and urea treatments showed a significant increase at first and then a significant decrease.The AOB abundance increased with ammonia chloride treatment.The AOB abundance of ammonia chloride treated soil was significantly lower than that of ammonia sulfate and urea treated soil at 14 days.In the four treatments,there was no significant change in the copy number of AOA amoA gene in the process of incubation.In the 28 d incubation,the AOB amoA gene copies in?T?and?T N?treatments were significantly higher than those of AOB amoA gene copies in?F?and?F N?treatments.The number of AOB aomA gene copies in the?F?and?F N?treatment was not significantly changed during the28 d incubation,and the magnitude of the aomA gene copy number was only 4 times.At 0 d,the copy number of AOB aomA gene in F+5%T N was significantly higher than that in long term recreational soil.The copy number of AOB aomA gene increased in incubation process,and increased from 15.93 d 106 g^-11 at 0 d to 31.43*106 g^-11 at 28 d.The copy number of AOA aomA gene in?T?and?T N?treatment was significantly higher than that of?F?and?F N?in the AOA amoA gene copy number.At 0 d,the copy number of AOA aomA gene in F+5%T N was significantly higher than that in long term recreational soil.The copy number of AOA aomA gene increased in incubation process,and increased from 12.99 d 106 g^-11 at 0 d to 39.42*106 g^-11 at 28 d.Calcareous purple soil,long-term fallow soil tillage and fertilization in soil and the dominant species were Nitrosospira AOB Cluster 3,the dominant species in calcareous purple soil is AOA Group 1.1b,NOB Nitrospira as the dominant species,long-term fallow soil AOA amoA Group 1.1b and Group 1.1 gene a associated accounted for the major.The main conclusions of this study are as follows:?1?the addition of substrate nitrogen can promote the occurrence of nitrification;?2?NH₄Cl could delay the accumulation of nitrate nitrogen and inhibit the nitrification;?3?the main promoter of nitrification in calcareous purple soil is AOB,and the addition of substrate nitrogen source has a significant effect on AOB,and the chloride ion has a inhibition to AOB;?4?the nitrification of the long-term leisure soil became extremely weak compared with the tillage soil,and the nitrogen source could not significantly promote the nitrification;?5?the abundance of AOB in long-term recreational soil is two orders of magnitude lower than that of tillage and fertilization soil,while the abundance of AOA in long-term recreational soil is relatively high.The leading factor of nitrification in long term recreational soil may be AOA;?6?the dominant population of AOB in neutral and calcareous soil is Nitrosospira Cluster 3,while AOA amoA functional gene group Group 1.1b and Group 1.1 A associated account for the most;?7?after long term leisure,the abundance and activity of AOB decreased significantly,while AOA became the dominant microorganism in nitrification.It further showed that AOA was more suitable for oligotrophic nitrogen environment.