ABSTRACT

Nitrogen-based fertilizer applications have an effect on nitrification and nitrifying microorganisms in acidic soils of agricultural and forest lands. However, the effect of different nitrogen (N) fertilizers on nitrification and nitrifying microorganisms in acidic Ultisols of the subtropical regions are not well studied. Here, we investigated the effect of ammonium sulfate and urea applications on nitrification and nitrifying microorganisms in acidic Ultisols of Jinyun Mountain. The abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) amoA genes were quantitatively analyzed by real-time PCR. Our results indicated that there was a significant difference in soil pH among treatments and the maximum pH value (pH = 4.93) was recorded in urea addition due to the hydrolysis of urea. Similarly, significant differences in the content of NH₄⁺-N and NO₃⁻-N were observed among treatments. The result also revealed that urea addition had higher ammonium and nitrate than that of ammonium sulfate, and stimulated nitrification in acidic Ultisols, whereas nitrification was not stimulated by the application of ammonium sulfate. The net nitrification rate at the end of the experiment for control, ammonium sulfate, and urea treatment were −0.005, −0.003 and 0.004 mg N kg⁻¹ soil day⁻¹ respectively. Besides, the addition of urea significantly increased the AOA and AOB abundance. The abundance of AOA amoA gene was greater than AOB in all treatments. However, the ratio of AOA to AOB was lower in soils with ammonium sulfate and urea addition compared to control. This implies that N addition greatly stimulates AOB rather than AOA abundance. Therefore, AOB may be responsible for the higher nitrification potential in the urea added soil. In conclusion, urea addition significantly increased the content of ammonium, soil pH, AOA and AOB abundance, and stimulates nitrification. AOB may play a significant role in nitrification process in urea added acidic Ultisols.

摘要

氮肥施用对农林地酸性土壤中的硝化作用和硝化微生物有影响。然而，不同氮（N）肥对亚热带地区酸性 Ultisol 中硝化和硝化微生物的影响尚未得到很好的研究。在这里，我们研究了硫酸铵和尿素的应用对缙云山酸性 Ultisol 中硝化和硝化微生物的影响。氨氧化古细菌（AOA）和氨氧化细菌（AOB）amoA的丰度通过实时 PCR 对基因进行定量分析。我们的结果表明，处理之间土壤 pH 值存在显着差异，并且由于尿素水解，在添加尿素时记录了最大 pH 值（pH = 4.93）。类似地，在处理之间观察到NH ₄ ⁺ -N 和NO ₃ ^- -N含量的显着差异。结果还表明，尿素添加比硫酸铵具有更高的铵和硝酸盐，并在酸性 Ultisol 中刺激硝化作用，而硝化作用不受硫酸铵的刺激。对照、硫酸铵和尿素处理实验结束时的净硝化速率分别为 -0.005、-0.003 和 0.004 mg N kg ^-1土壤日^-1分别。此外，尿素的加入显着增加了AOA和AOB丰度。AOA amoA基因的丰度在所有处理中均大于AOB。然而，与对照相比，添加硫酸铵和尿素的土壤中 AOA 与 AOB 的比率较低。这意味着 N 添加极大地刺激了 AOB 而不是 AOA 丰度。因此，AOB 可能是添加尿素的土壤中较高硝化潜力的原因。综上所述，尿素的添加显着增加了氨氮含量、土壤 pH 值、AOA 和 AOB 丰度，并刺激了硝化作用。AOB 可能在尿素添加酸性 Ultisol 中的硝化过程中起重要作用。