Importance of Permafrost for Water Cycle and Vegetation in East Siberian Taiga

East Siberian taiga is a unique ecosystem, which is established on permafrost. Climate there is extremely dry (about 250mm of annual mean precipitation). Oxygen and hydrogen isotope ratios of precipitation, soil water, sap water of plants, river, surface water, and atmospheric water vapor were observed in deciduous boreal forest near Yakutsk, Russia, to investigate the water flow in the ecosystem. Isotopic composition of precipitation characteristically changed during spring from low delta value (winter) to high delta value (summer), because of the change in the isotopic composition of water vapor. Transpired water by plants, namely, recycling of water from the surface through plants, may contribute the isotopic composition of atmospheric water vapor. Stable isotope ratio of sap water in plants and soil water were different between wet summer and dry summer. Sap water delta values were high during dry summer, and low during drought. This result indicated that rain water was used by plants when plants received enough summer rain, while melt water from permafrost was taken up by plants during drought. Isotopic composition of soil water indicated that water was transported upward in the soil during dry summer, while, rain water percolated downward during wet summer. Soil has a function for a storage of water in the permafrost region, and stored water in the soil can be a direct source of water for vegetation during drought.