施氮对水稻土N_2O释放及反硝化功能基因(narG/nosZ)丰度的影响

Effect of N application on the abundance of denitrifying genes(narG/nosZ) and N_2O emission in paddy soil

以紫潮泥和红黄泥两种不同质地的水稻土壤作为研究对象,通过室内培养试验,分析施用硝态氮肥对N2O释放和反硝化基因(narG/nosZ)丰度的影响,并探讨反硝化基因丰度与N2O释放之间的关系。结果表明,施用硝态氮显著增加两种水稻土的N2O释放量。在72h培养过程中,施氮改变了紫潮泥反硝化基因(narG/nosZ)的丰度,但并未明显影响红黄泥反硝化基因(narG/nosZ)丰度。通过双变量相关分析发现,除了紫潮泥narG基因外,其它的反硝化基因丰度和N2O释放之间并没有显著相关性。

Nitrous oxide （N2O） is a powerful greenhouse gas with a global warming potential 296 times higher than carbon dioxide over a 100-year time period. Most of N2O is emitted from agricultural soils through microbial processes of nitrification and denitrification. In order to explore the relationship between N2O emission and denitrifying processes in paddy soil, incubation experiment was performed with purple calcareous clayey soil （P） and reddish yellow loamy soil （R） with CK and N treatments. According to N2O emission rate, soil samples were taken at 24, 48 and 72 hours which represented the growing, top and dropping periods, respectively. The abundances of narG and nosZ were analyzed using real-time PCR. The results showed that N2O emission in N treatment was significantly higher than that in CK treatment in the two paddy soils, indicating that application of NO3- greatly contributed to N2O emission. Compared the two soils treated with nitrogen, N2O flux behaved differently, in the purple calcareous soil N2O emission rates were significantly lower in 24thh in comparison with the incubation time at the 48th and 72thh which possessed similar flux rates. However, the reddish yellow loamy soil showed that the emission rate was the highest at 48thh, afterwars it dropped till 72thh the rate was significantly lower than that at 48thh. Compared to purple calcareous soil, the N2O emission in N treatment was higher in reddish yellow loamy soil, which increased 26.9%, 38.7% and 17.0% in 24thh, 48thh and 72thh, respectively. After 72 h incubation, the content of NO3--N decreased 18%and 40% in purple calcareous soil and reddish yellow loamy, indicating more NO3--N was tansformed in reddish yellow loamy than that in purple calcareous soil. The real-time PCR revealed that N application affected the abundance of the denitrifying genes in the purple calcareous clayey soil, but didn＇t obviously affect them in the reddish yellow loamy soil. For purple calcareous clayey soil, narG gene abundance in N treatment were significantly higher than that in its CK treatment at all the three incubation time points （24thh, 48thh, 72thh）, while there was no significantly difference for reddish yellow loamy soil except for in 48thh with higher narG gene abundance in N treatment. Meanwhile, application of nitrogen induced a higher abundance of nosZ gene than that in the CK treatment only at 48thh for purple calcareous clayey soil and no significantly difference was detected for reddish yellow loamy soil. Bivariate correlation analysis showed that no significant correlations were found between abundance of denitrifying genes （narG /nosZ） and N2O emission, except narG gene in purple calcareous clayey soil. The results suggested that studying correlationship between gene abundance and N2O emission from DNA level might have some limitations, because not all of DNA quantified in real-time PCR was expressed and the denetrifying DNA gene just represented the denetryfying bacterial potential physiological function. So it is more accurate to study correlation from RNA level as RNA translated denitryfing oxide-reductase is realtime correlation of N2O emission.