Dynamics of N2O production and reduction processes in a soybean field revealed by isotopocule analyses

Sakae Toyoda, Fadwa Damak, Shohei Hattori, Masanori Takeda, Hiroko Akiyama, Yuma Sasaki, Kiwamu Minamisawa

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1 Citation (Scopus)

Abstract

Agricultural soils are the largest anthropogenic source of atmospheric nitrous oxide (N2O) that causes global warming and stratospheric ozone depletion. In addition to the well-known emission associated with fertilization, significant N2O emission during the harvest season has been reported for soybean fields. Because soybean production is increasing, it is important to understand the production and consumption mechanisms of N2O in soybean fields. This study aimed to identify the microbial production processes using the ratios of isotopically substituted molecules, isotopocules. We also investigated the effectiveness of inoculating soybean with symbiotic nitrogen-fixing soil bacteria (rhizobia) with a high N2O-reducing ability, which was suggested as a mitigation option for N2O emission from soybean fields, on the basis of the characteristic isotope effect during N2O reduction. Along with semi-continuous flux measurements, weekly sampling and analysis of soil-emitted gas and soils were conducted in an experimental soybean field for two periods, after fertilization and before harvest, in two successive years. The isotopocule ratios of N2O emitted after fertilization suggested that it was produced by bacterial denitrification and nitrifier denitrification with smaller contributions from nitrification and fungal denitrification. Those for preharvest emission showed that N2O was produced by bacterial denitrification, including the process mediated by nodule rhizobia, with little progress of N2O reduction. We could not detect any difference between soybeans inoculated with rhizobia with different N2O reducing activity (nosZ− dominant, nosZ+, and nosZ++) because of the weak N2O reduction, probably due to relatively aerobic soil conditions. Since temporal changes in the N2O isotopocule ratios further implied that the rate of N2O reduction decreased in the later phase of autumn emission, suitable soil conditions are crucial for effective N2O reduction by inoculation of high nosZ-expressing rhizobia.

Original languageEnglish
Article number109358
JournalSoil Biology and Biochemistry
Volume191
DOIs
Publication statusPublished - 2024 Apr

Keywords

  • Denitrification
  • NO reduction
  • Rhizobium
  • Stable isotope ratios

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