Researches On The Characteristics Of Nitrogen Mineralization Of Soil In The Southern And Northern Paddy Field Under Culture Conditions

There were still a few problems for N mineralization process. Thesis studied the effect of pre-incubation temperature on N mineralization as well as fixed ammonium, variation of microorganism composition in the N mineralization process through lab incubation. The ammonium N and fixed N content were tested before and after the experiment, the change of soil org anic N components in the pre-incubation process or the mineralization process were analyzed, the CO2 content was examined during incubation process and the soil DNA was extracted and Miseq sequenced. In order to resolve the deficiencies in N mineralization studies and provide support for a comprehensive understanding for N mineralization in paddy soil. The main findings were as follows:Soil N supply process were not changed significantly in 12 ℃ pre-incubation temperature, so 12 ℃ can be used as a suitable pre-incubation temperature. Experiment results showed that with the increase of pre-incubation temperature, the initial ammonium N increased, but the mineralization N rate significantly reduced. Mineralization N rate was negative or a little when the pre-incubation temperature was increased to 35 ℃. Although the 12 ℃ and 25 ℃ pre-incubation temperature did not reduce the total amount of soil mineralized N, model fitting displayed the mineralization process of air-dried soil was different from soil after pre-incubation. The content of hydrolysamino acid N was increased and the acid insoluble N in soil was decreased after air-dried soil directly incubated for 2 weeks or after 25 ℃ pre-incubation. Compared with air-dried soil, the content of organic N for 12 ℃ pre-incubation was not significantly different. With the increasing of pre-incubation temperature, the content of hydrolysamino acid N increased first and then decreased, the acid insoluble N decreased first and then increased. These results indicated that the acid insoluble N may also play an important role in the mineralization process, and the composition of organic N made a significant change when the pre-incubation temperature was higher than 25 ℃. This resulted in changing of the process of soil N mineralization process. On the contrary, the organic N forms and soil N mineralization process changed a little when pre-incubation temperature was 12 ℃, the mneralization process was more realistic.The reduced mineralization N in long-term incubation was not related to the fixed ammonium. As the temperature increasing, the southern soil mineralization N content increased and it was the highest in 35 ℃. For northern soil, when the temperature rose from 25 ℃ to 35 ℃, mineralization N content increased little. As the temperature increasing, southern soil fixed ammonium content increased, but the northern soil was not. With the incubation time incre asing, the mineralization N content increased first(0 d-21 d)and then dropped(21 d-35 d), as well as fixed ammonium content. Compared with the beginning, after 21 days incubation, the southern soil fixed ammonium content increased by an average of 15 %, corresponding to the northern soil increased by 7 %; from 21 to 35 days, the southern soil fixed ammonium content reduced 0.2%-6% and the northern soil fixed ammonium reduced 7%-14%. In the later stage of incubation, the content of fixed ammonium in soil decreased with the soil mineralization N. Therefore, the decreased of mineralization N in the later stage was not fixed to the fixed ammonium.Southern soil microorganisms did not endure to low temperature, while the high temperature inhibited the activity of northern soil microorganisms.With the incubation temperature increasing, southern soil bacterial abundance increased; with incubation time increasing decreased. At the beginning stage(0-14 d), northern soil bacterial abundance did not response to the temperature, but at the end of incubation, northern soil bacterial abundance dropped the most in 40 ℃, lower than other two temperature with significant difference. Southern soil bacterial richness index and diversity index under the condition of 15 ℃ were the lowest, northern soil bacterial richness and diversity index under the condition of 40 ℃ were the lowest and the difference was significant(P < 0.05). CO2 production rate and soil inorganic N content were proportional to the temperature, it could be explained that the bacterial activity is directly proportional to the temperature. Southern soil bacterial abundance was higher than northern soil, therefore CO2 production content and inorganic nitrogen were higher than northern soil. The amount of mmonia-oxidizing archaea(AOA) and ammonia-oxidizing Bacteria(AOB) in southern soil were higher than northern soil, leading to nitrate N content was higher than northern soil.