Graduate School of Life Sciences, Tohoku University
The term “rhizosphere” was first coined in 1904 by Lorenz Hiltner in Germany, who had a special interest in N transformations around leguminous nodules in fields. Our group has revealed active N transformation including N2O in soybean rhizosphere. A 15N tracer experiment indicated that the N2O was derived from N fixed in the nodules. As for nitrification, the addition of nitrification inhibitors significantly reduced N2O flux. Both AOA and AOB were detected by PCR analysis with increase of N2O flux in soybean rhizosphere. 15N experiment and fungal isolation indicated that nitrite-utilizing fungi including Fusarium species substantially mediate N2O emission in soybean rhizosphere. Inoculation experiments with soybean bradyrhizobia showed that they contribute to both production and consumption of N2O via bacterial denitrification. From these results, the organic-N inside of the nodules was mineralized to NH4+-, and N2O-producing processes simultaneously occur in soybean rhizopsphere via bacterial nitrification, fungal denitrification and rhizobial denitrification, which provides a textbook for microbial N cycle in the environments.
keywords:Nitrogen cycle,Denitrification,Nitrification,Rhizosphere,Nitrous oxide