Changes in Denitrification Potentials and Riverbank Soil Bacterial Structures along Shibetsu River, Japan

Abstract

Riverbank soil ecosystems are important zones in terms of transforming inorganic nitrogen (N), particularly nitrate (NO3−-N), in soils to nitrous oxide (N2O) gases. Thus, the gasification of N in the riverbank soil ecosystems may produce a greenhouse gas, N2O, when the condition is favourable for N2O-producing microbes. One of the major N2O-producing pathways is denitrification. Thus, we investigated the denitrification potentials along Shibetsu River, Hokkaido, Japan. We sampled riverbank soils from eight sites along the Shibetsu River. Their denitrification potentials with added glucose-carbon (C) and NO3−-N varied from 4.73 to 181 μg·N·kg−1·h−1. The increase of the denitrification after the addition of C and N was negatively controlled by soil pH and positively controlled by soil NH4+-N levels. Then, we investigated the changes in 16S rRNA bacterial community structures before and after an anaerobic incubation with added C and N. We investigated the changes in bacterial community structures, aiming to identify specific microbial species related to high denitrification potentials. The genus Gammaproteobacteria Aeromonadaceae Tolumonas was markedly increased, from 0.0 ± 0.0% to 16 ± 17%, before and after the anaerobic incubation with the excess substrates, when averaged across all the sites. Although we could not find a significant interaction between the denitrification potential and the increase rate of G. Aeromonadaceae Tolumonas, our study suggested that along the Shibetsu River, bacterial response to added excess substrates was similar at the genus level. Further studies are needed to investigate whether this is a universal phenomenon even in other rivers.

Soil microorganisms and methane emissions in response to short-term warming field incubation in Svalbard

“…The class Gammaproteobacteria is known as one of the denitrifier groups, and many species of this class are coldadapted. It thus might be an important group to determine the capacity of Arctic rivers to remove excess nitrogen (Franco et al, 2017;Uchida et al, 2018;Qian-Qian et al, 2021). More importantly, long-term warming rather than short-term induced changes in the composition of soil microbial communities can cause sustained changes in microbial activity, resulting in soil carbon emissions.…”

Delineation of Nitrate Reduction Hotspots in Artificially Drained Areas through Assessment of Small-Scale Spatial Variability of Electrical Conductivity Data

“…Nitrate reduction in the unsaturated zone across different types of Danish soils has not been fully assessed as most studies are carried out under controlled laboratory conditions that are meant to describe the possible spatial and temporal heterogeneity under field conditions [11]. Denitrification potential [12][13][14], oxygen, organic carbon, and nitrogen species levels [13,15] are among the factors that have been used as variables for describing the heterogeneity of nitrogen reduction. Since these variables usually involve extensive sample collection and laboratory work, and are generally destructive, the sample sizes are often small and locations must be carefully selected to properly represent spatial characteristics [15,16].…”