[M-IS14] Biogeochemistry

[MIS14-16] Estimation of the nitrogen cycle and plant nitrogen source using nitrogen isotope analysis in dryland ecosystem, Northeast Asia.

*Tanaka-Oda Ayumi¹, Izuki Endo², Nobuhito Ohte³, Midori Yano⁴, Akiko Makabe⁵, Keisuke Koba⁶, Jamsran Undarmaa⁷, Norikazu Yamanaka⁸, Ken Yoshikawa⁹ (1.Forestry and Forest Products Research Institute, 2.School of Human Science and Environment, University of Hyogo, 3.Graduate School of Informatics, Kyoto University, 4.Institute for Agro-Environment Sciences, NARO, 5.Japan Agency for Marine-Earth Science and Technology, 6.Center of ecological research, Kyoto University, 7.Mongolian University of Life Sciences, 8.Arid Land Research Center, Tottori University, 9.Academic and General Okayama University Regional Research Association, Okayama University)

Keywords:Nitrogen isotope ratio, Nitrogen cycle, dryland ecosystem

Nitrogen (N) is one of most restricted nutrient for plant growth in the dryland ecosystems; it is still unclear the mechanisms of plants nutrients absorption from the dry soil. The N isotope ratio (δ¹⁵N) of organic and inorganic N reflects N cycle and it also used for estimation of plant N source by comparison with δ¹⁵N value in the plants. To better understand the N cycle and plant N uptake in the dryland ecosystem, we analyzed N content and δ¹⁵N value of soils and plant foliage in the Mongolian Gobi steppe. We established four typical vegetation plots based on the dominant plant species and topographical conditions; river bottom with halophyte species, riverbank with a large perennial grass community, the upper slope with an isolate grass communities and flat plain with annual forbs. We sampled soil from five depth of the vertical soil layer from the vegetation plots and measured extracted dissolved organic and inorganic N content and δ¹⁵N values. We also measured above- and belowground length, N content (N%) and δ¹⁵N values. The plants root mostly distributed in the 10-15 cm depth soil layer. The soil inorganic N concentration was extremely limited expect under the large grass communities. The δ¹⁵N values of soil nitrate were corresponded with the perennial grass species, while in the other species often had higher δ¹⁵N values than soil nitrogen source. From these results, indicated that N cycle in the dryland ecosystems significantly varied with aboveground vegetation and nitrate was one of N source of perennial grass species. For the other plant species dissolved organic N which had higher δ¹⁵N values may have some role for N source in the dryland ecosystem.