N(2)O emission from degraded soybean nodules depends on denitrification by Bradyrhizobium japonicum and other microbes in the rhizosphere.
N(2)O emission from degraded soybean nodules depends on denitrification by Bradyrhizobium japonicum and other microbes in the rhizosphere.
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DOI：
10.1264/jsme2.me12100
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发表时间：
2012
影响因子：
2.2
通讯作者：
Minamisawa K
中科院分区：
文献类型：
--
作者：
Inaba S;Ikenishi F;Itakura M;Kikuchi M;Eda S;Chiba N;Katsuyama C;Suwa Y;Mitsui H;Minamisawa K
利用实验室开发的降解大豆根瘤产生 N2O 排放的模型系统来阐明大豆田 N2O 排放的机制。接种 nosZ 缺陷型慢生根瘤菌 USDA110 菌株（ΔnosZ，缺乏 N2O 还原酶）的大豆植物在无菌罐中生长。 30天后，应用芽头斩首（D，以促进根瘤降解）、添加土壤（S，以供应土壤微生物）或两者（DS）。仅在 DS 处理时才会排放 N2O。因此，土壤微生物和根瘤降解都是大豆根际 N2O 排放所必需的。 DS 处理后 15 天，N2O 通量达到峰值。硝酸盐的添加显着增强了 N2O 排放。 15N示踪实验表明N2O来源于固定在结节中的N。为了评估缓生根瘤菌的贡献，比较了 nirK 突变体（ΔnirKΔnosZ，缺乏亚硝酸还原酶）和 ΔnosZ 之间的 N2O 排放。 ΔnirKΔnosZ 根际的 N2O 通量显着低于 ΔnosZ，但仍为 ΔnosZ 的 40% 至 60%，表明 N2O 排放是由 B. japonicum 和其他土壤微生物共同造成的。只有 nosZ 感受态 B. japonicum（nosZ+ 菌株）才能吸收 N2O。因此，在根瘤降解过程中，日本芽孢杆菌和其他土壤微生物都通过反硝化过程从根瘤氮中释放N2O（N2O源），而nosZ-competent B. japonicum则专门吸收N2O（N2O汇）。大豆根际的 N2O 净通量可能由 N2O 源库平衡决定。
A model system developed to produce N2O emissions from degrading soybean nodules in the laboratory was used to clarify the mechanism of N2O emission from soybean fields. Soybean plants inoculated with nosZ-defective strains of Bradyrhizobium japonicum USDA110 (ΔnosZ, lacking N2O reductase) were grown in aseptic jars. After 30 days, shoot decapitation (D, to promote nodule degradation), soil addition (S, to supply soil microbes), or both (DS) were applied. N2O was emitted only with DS treatment. Thus, both soil microbes and nodule degradation are required for the emission of N2O from the soybean rhizosphere. The N2O flux peaked 15 days after DS treatment. Nitrate addition markedly enhanced N2O emission. A 15N tracer experiment indicated that N2O was derived from N fixed in the nodules. To evaluate the contribution of bradyrhizobia, N2O emission was compared between a nirK mutant (ΔnirKΔnosZ, lacking nitrite reductase) and ΔnosZ. The N2O flux from the ΔnirKΔnosZ rhizosphere was significantly lower than that from ΔnosZ, but was still 40% to 60% of that of ΔnosZ, suggesting that N2O emission is due to both B. japonicum and other soil microorganisms. Only nosZ-competent B. japonicum (nosZ+ strain) could take up N2O. Therefore, during nodule degradation, both B. japonicum and other soil microorganisms release N2O from nodule N via their denitrification processes (N2O source), whereas nosZ-competent B. japonicum exclusively takes up N2O (N2O sink). Net N2O flux from soybean rhizosphere is likely determined by the balance of N2O source and sink.
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