[M-IS22] Biogeochemistry

[MIS22-P09] Soil nitrogen cycle in larch forests and various vegetation of the Mongolian forest steppe

*Ayumi ODA¹, Taiga Masumoto¹, Hitomi Oigawa¹, Naoki Makita¹, Kho YASUE¹, Tetsuoh Shirota¹, Yojiro Matsuura², Davaajav Dalkhsuren³, Gerelbaatar Sukhbaatar³, Baatarbileg Nachin³, Keitaro Fukushima⁴, Yuji Onishi⁵, Keisuke Koba⁶ (1.Shinshu University, 2.Forestry and Forest products Research Institute , 3.National University of Mongolia, 4.Fukushima University, 5.Research Institute for Humanity and Nature, 6.Kyoto University)

Keywords:Forest steppe, Organic matter dynamics, Larch forest, Inorganic nitrogen

The larch forests of the Mongolian forest steppe are an area where the effects of global warming, dryness and the increasing frequency of forest fires are becoming apparent. There are places where the original vegetation of larch forest has been replaced by mixed forests and grasslands, and places where the forest has not recovered after a fire, and these exist in a mosaic-like pattern. We conducted soil profile surveys and measured the amount of nitrogen and isotope ratios in the soil at each area. As a result, there were no differences in the water content, bulk density or fine earth ratio of the soil collected from each location, but the ash content of the fine earth was higher in the grassland than in the larch forest or mixed forest, and it was thought that there was more organic matter in the fine earth fraction in the forest. Similarly, the nitrogen content of the soil was lower in the grassland than in the forest. Although the level of TDN (total dissolved nitrogen) in the soil, which is the substrate for the nitrogen cycle, was similar in the forest and the grassland, the concentration of ammonia nitrogen was high in the larch forest and the larch-birch mixed forest, while the concentration of nitrate nitrogen tended to be high in the grassland and in places where the forest had not recovered after a fire. The results suggest that when forests decline, the supply of fine root litter and other organic matter to the soil decreases, and there is a possibility that the dynamics of organic matter in the soil and the nitrogen cycle will change.