Isotopic evidence for seasonality of microbial internal nitrogen cycles in a temperate forested catchment with heavy snowfall

Shohei Hattori; Yoshio Nuñez Palma; Yuko Itoh; Moeko Kawasaki; Yoichi Fujihara; Keiji Takase; Naohiro Yoshida

doi:10.1016/j.scitotenv.2019.06.507

Isotopic evidence for seasonality of microbial internal nitrogen cycles in a temperate forested catchment with heavy snowfall

Sci Total Environ. 2019 Nov 10:690:290-299. doi: 10.1016/j.scitotenv.2019.06.507. Epub 2019 Jul 2.

Authors

Shohei Hattori¹, Yoshio Nuñez Palma², Yuko Itoh³, Moeko Kawasaki⁴, Yoichi Fujihara⁵, Keiji Takase⁵, Naohiro Yoshida⁶

Affiliations

¹ Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4529 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan. Electronic address: hattori.s.ab@m.titech.ac.jp.
² Department of Environmental Chemistry and Engineering, Interdisciplinary Graduate School of Science and Engineering and Engineering, Tokyo Institute of Technology, 4529 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan.
³ Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
⁴ Nakanoto General Agriculture and Forestry Office, Ishikawa Prefecture, 33 Ni-bu, Kojima-machi, Nanao, Ishikawa 926-0852, Japan.
⁵ Faculty of Bioresources and Environmental Sciences, Ishikawa Prefectural University, 1-308, Suematsu, Nonoichi, Ishikawa 921-8836, Japan.
⁶ Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4529 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan; Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan.

PMID: 31291607
DOI: 10.1016/j.scitotenv.2019.06.507

Abstract

The Hokuriku district of central Japan receives high levels of precipitation during winter, largely in the form of snow. This study aimed to elucidate the internal nitrogen dynamics in this temperate forested region with heavy snowfall using the triple oxygen and nitrogen isotopic compositions of NO₃^-. The isotopic compositions of NO₃^- in atmospheric depositions (P and Tf), with terrestrial components of the soil layer (A0, S25, S55, and S90), ground water (G), and output (St) were measured from 2015 to 2016 in a forested catchment located in the southern area of the Ishikawa Prefecture, Japan. Seasonal distributions of Δ¹⁷O(NO₃^-) showed a decreasing trend from the inputs to outputs of the ecosystem. We found relatively constant Δ¹⁷O(NO₃^-) values in the output components (G and St), but found highly fluctuating Δ¹⁷O(NO₃^-) values resulting from the seasonal variations in the nitrification activity within soil waters. Specifically, we observed a lower nitrifying activity in the top soil layer throughout cold periods, presumably due to the input of cold melted snow water. The general trend of increasing δ¹⁵N(NO₃^-) value from the input to output components, with the changes in denitrification hotspots from shallow to deeper soil layer, can be observed between warm and cold periods. Thus, the seasonal changes of hotspots related to microbial nitrification and denitrification could be noted due to the seasonal changes in the isotopic compositions of nitrate. The estimated ecosystem-scale gross nitrification and denitrification rates are low; however, the output components are relatively stable with low concentrations of nitrate, indicating that the plant uptake of nitrogen most probably occurs at greater rates and scales in this forested ecosystem. Future nitrogen deposition and the vulnerable dynamics of snow melting are likely to have impactful consequences on such localities.

Keywords: Denitrification; Ecosystem; Isotopes; Nitrate; Nitrification.

MeSH terms

Environmental Monitoring*
Forests*
Japan
Nitrogen / analysis*
Nitrogen Cycle*
Seasons
Snow / chemistry*

Substances

Nitrogen