[A-CG30] Material circulations in Terrestrial Ecosystem: Water, Carbon and Nitrogen etc.

[ACG30-05] Spatial variations in larch and soil nitrogen isotope ratio along forest-grassland gradient in northern Mongolia

*Rei FUJIYOSHI¹, Maki TSUJIMURA², Larry c.m. LOPEZ³, Atsuko SUGIMOTO⁴ (1.Graduate School of Environmental Science, Hokkaido University, 2.Faculty of Life and Environmental Sciences, University of Tsukuba, 3.Faculty of Agriculture, Yamagata University, 4.Faculty of Environmental Earth Science, Hokkaido University)

Keywords:ecotone, Mongolia, nitrogen isotope ratio, plant and soil

The underlying processes that affect the Nitrogen isotope ratio of plant and soil,which is known as a good indicator of N dynamics and shows dependency on climate, is not yet clearly understood.
In this study, we compare the nitrogen isotope ratio of single plant species (Larix sibirica Ledeb.) and soils along the forest-grassland gradient of a forest-steppe ecotone in Mongolia. Larch needles and soils were sampled during the growing season (May- August) from 2004-2012 at several sites in seven study areas.
The results showed the clear spatial pattern in needle, soil nitrogen isotope ratios, and its difference (Δδ¹⁵N)along forest-grassland gradient and the pattern corresponded to humus type (mor/mull). Δδ¹⁵N also had significant correlations with needle δ¹³C and C/N ratio of bulk soil, suggesting the Δδ¹⁵N change relates to water, light conditions and soil N availability. Isotope mass-balance model was applied to investigate the processes affecting the spatial pattern of Δδ¹⁵N.