| Nitrous oxide (N2O) is a potent greenhouse gas, and is also an important precursor to compounds contributing to depletion of stratospheric ozone. N2O from agricultural system contributes to over half of the anthropogenically induced N2O emission. The variation of soil N2O emission temperature sensitivity is very large, and can be differently responsive to future climate change. However, the microbial mechanisms of soil N2O emission temperature sensitivity are still not clear. The combined applications of urea and nitrification inhibitors, and organic and inorganic fertilizers can strongly affect soil N2O emission. In this study, we studied the effect of urea and nitrification inhibitor applications on N2O emission and their associated microbial mechanisms. Also, by selecting a porper nitrification inhibitor, we studied soil N2O emission temperature sensitivity and their related microbial mechanisms through different pathways. Meanwhile, by investigating different soil types across China, we summarized the indictors that influence N2O emission temperature sensitivity and its related microbial mechanisms.Our results indicated that:(1) In alluvial soil and black soil, N2O emissions were increased by the addition of urea, and then decreased by the addition of nitrification inhibitor (Nitrapyrin). The stimulation and suppression of N2O emission by urea and NP occurred alongside fluctuation in the growth of AOB in alluvial and paddy soils. Weak stimulation and suppression of N2O emissions by urea and NP corresponded with weak effects on AOB abundances in the black soil. Changes in N2O emissions were not significantly correlated with AOA abundances in any of the three soils. The community structure of AOB in alluvial soil was significantly changed by the addition of urea. No difference was found in the community structures of AOB in black soil and paddy soil, and in the community structures of AOA in all three soils. The results showed that differential responses of N2O emission to urea and NP application in arable soils could be mainly explained by differences in growth of ammonia oxidizing bacteria; (2) Acetylene and nitrapyrin of different concentrations could inhibit N2O emitting from the addition of urea. The inhibition of nitrapyrin in low concentration was poor, and the inhibition effect of nitrapyrin in high concentration was not as good as acetylene in the later stage of the incubation. Acetylene was a more proper method for nitrification inhibition in long-time incubation experiments; (3) Long-term fertilization significantly increased the temperature sensitivity of soil N2O emission. The ratio of N2O emitted through denitrification pathway to total N2O emission was higher in organic fertilizer-treated soil than in inorganic fertilizer-treated soil. The abundances and community structures of ammonia oxidizers and denitrifiers were significantly changed by long-term fertilizations. Only the nirS community structure was sensitive to temperature change, and a strong correlation was observed between nirS gene abundance and potential N2O emissions. Relationships between AOA, nirK gene abundances and potential N2O emission were significant but relatively weak. Besides direct effect, potential N2O emission was also indirectly influenced by temperature through mediation of NH4+ concentration and nirS-type denitrifier. Our work suggests that warming-induced elevation of potential N2O emission could be strengthened by long-term application of fertilizers, especially organic manure, via shifting community abundance and structure of nirS-type denitrifier; (4) In the investigation into 12 major soil types all over the country, soil N2O emission temperature sensitivity (Q10) was strongly related to soil texture, total nitrogen content, soil organic matter content, soil nitrate and ammonium nitrogen content, but was not related to pH value. Basically, Q10 was lower as the soil is more clayey. In clay soils, we assumed that the N2O emission temperature sensitivity was regulated through abiotic pathway. However, in loam soils, the effect of temperature on N2O emission was through microbial denitrification pathway, with nirS-type denitrifier play the key role. The dissolved organic nitrogen content was of vital importance to the temperature sensitivity of N2O emission in all soils.The results of this study revealed that soil N2O emission temperature sensitivity could be notably increased by long-term fertilization; denitrification process is the main pathway that contributes to the temperature sensitivity in the black soil used. Furthermore, the temperature sensitivity of N2O emission was correlated with soil texture. The N2O emission temperature sensitivity in clay soils was regulated through abiotic pathway, while N2O emission temperature sensitivity in loam soils was through microbial denitrification pathway. For the nitrification pathway, the strong stimulation and suppression of N2O emission caused by addition of urea and NP was in line with the growth of AOB. |
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