First microscale data on depth profiles of microbial N₂O reduction, O2 availability, and pore networks inside contrasting single soil aggregates

S. Mitsunobu, R. Wagai, H. Shimada, Hiromi Kato, K. Ito, S. Sato, M. Hayatsu, K. Minamisawa

Research output: Contribution to journalArticlepeer-review

Abstract

A major greenhouse gas, nitrous oxide (N2O) significantly emitted from agricultural soils, is reduced to innocuous N2 gas by the activity of two groups of N2O-reducing microbes (typical clade I and more recently discovered atypical clade II) having different enzymatic efficiency. Yet, basic information such as the locations of N₂O reduction hotspots and soil factors regulating their formations is still lacking. In addition, oxygen availability, which is strongly constrained by soil pore property, likely dictates their ecology in soil as N2O reductase enzyme (coded by nosZ genes) is inhibited by O2. Accordingly, the aim of this study was to assess the mechanistic linkage among soil pore networks, chemical microenvironments (pH, Eh, and O2 and N2O abundances), ecology of N₂O-reducing microbes, and the occurrence of N₂O reduction hotspots in single soil aggregates. Using water-stable macroaggregates from two contrasting soil types (highly porous Andosol and less porous clay-rich Acrisol), we determined microscale depth profiles of N2O and O2 dynamics, three-dimensional pore properties, and the two N2O reducer populations in the single aggregates after 48-h lab incubation under a water-saturated condition. The N2O and O2 depth profiles showed the increase in N2O production with O2 depletion towards deeper part of the incubated aggregates, indicating denitrification N2O production especially in Andosol aggregate where O2 availability was higher. The gene distribution with depth clearly showed higher abundance of nosZ harboring microbes (including both clades I and II) in the Acrisol aggregate than Andosol aggregate especially towards the aggregate interior. In the Acrisol aggregate, the abundance of nosZ clade I harboring microbes was maximum at the middle depth corresponding to N2O maxima, whereas the nosZ clade II harboring microbes had slightly different niche as their population monotonically increased towards the aggregate core, which were consistent with theoretical O2 availability and pore connectivity. The current findings underscore the intimate connection between soil physical complexity and microbial ecology, which merits further investigation.

Original languageEnglish
Article number109684
JournalSoil Biology and Biochemistry
Volume202
DOIs
Publication statusPublished - 2025 Mar

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