JpGU-AGU Joint Meeting 2020

Presentation information

[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS25] Biogeochemistry

convener:Keisuke Koba(Center for Ecological Research, Kyoto University), Hideaki Shibata(Field Science Center fot Northern Biosphere, Hokkaido University), Naohiko Ohkouchi(Japan Agency for Marine-Earth Science and Technology), Youhei Yamashita(Faculty of Environmental Earth Science, Hokkaido University)

[MIS25-01] Competition for inorganic-N between soil microbes and plants?

*Keisuke Koba1 (1.Center for Ecological Research, Kyoto University)

Keywords:Nitrogen dynamics, Stable isotope, inorganic nitrogen

We all know that there must be competition for nitrogen, especially for inorganic nitrogen between soil microbes and plants in terrestrial ecosystems. Despite the long history of this topic, our understanding is still insufficient, especially for the modeling approaches for the projection of the ecosystem functions. Here we applied stable isotope natural abundance technique to the forested ecosystems in Japan to figure out how δ15N of plants, soil nitrogen, and soil microbial biomass (SMB) can tell us about the intact N competition between plants and soil microbes.

In this talk, I will present our new δ15N data of plants, soil nitrogen, and SMB in the forested ecosystems in Japan which illustrates that δ15N of SMB was totally different from δ15N of plants. δ15N of SMB was higher than δ15N of other N, i.e. bulk soil N, extractable organic and inorganic N, and plants. Since δ15N of SMB is controlled by the balance of N assimilation and N excretion (Collins et al. 2008; Shinoda et al. 2018), the higher δ15N of SMB is attributed to the soil N assimilation with N excretion (N mineralization). In other words, SMB utilized soil organic N with N mineralization. Since δ15N of plants shows the plant’s reliance on soil inorganic nitrogen, it is likely that there was no obvious competition for nitrogen between SMB (utilizing organic nitrogen) and plants (utilizing inorganic nitrogen). This is my quite preliminary data interpretation and I look forward to the discussion on our δ15N data in the talk.