Asami Nakanishi

Changes in nitrogen transformation in forest soil representing the climate gradient of the Japanese archipelago

Net nitrogen transformation was investigated under different climate conditions by soil transplantation and in situ incubation of forest surface soils using the resin-core method. Selected conditions were considered to reflect those of the natural climate gradient in the Japanese archipelago. Study sites were established in natural forests in northern Hokkaido (Uryu), northern Kanto (Kusaki), central Kinki (Kamigamo), and southern Kyushu (Takakuma), representing the northernmost to the southernmost island regions of Japan. Field experiments comparing soils incubated at “native” and “transplanted” sites were conducted from June 2008 to May 2009. Net production, accumulation, and leaching of soil ammonium (NH4+) and nitrate (NO3−) were measured at each of the sites during the growing season (June–October), the dormant season (November–May), and throughout the year. Net nitrate production was highest in Kusaki soil, especially during the growing season, whereas net ammonium production was highest in Uryu soil, the coldest site, especially during the dormant season. Net nitrate production increased significantly in soils transplanted to a warmer climate during the growing season. However, net ammonium production increased in soils transplanted to colder climates during the dormant season. These findings indicate that, with the exception of the infertile soil samples from Kamigamo, the range of natural climates in Japan has a significant effect on nitrogen availability in surface soil. In addition, the original characteristics of the nitrogen cycle of the surface soil from each native site were retained, even when marked changes in soil temperature (approximately 8°C) occurred after transplantation.

Chemical Characteristics in Stemflow of Japanese Cedar in Japan

To clarify the characteristics in stemflow of Japanese cedar (Cryptomeria japonica), we conducted the annual and extensive observation. We examined the chemistry of bulk and wet deposition, throughfall and stemflow at 26 forested sites in June and September 1998. The each sampling site was broadly distributed in all over the Japanese archipelago. The stemflow pH of Japanese cedar was significantly lower (p<0.01) than precipitation and stemflow of broad-leaved species in both months. There were significant anion deficits in stemflow of Japanese cedar, suggesting that organic anions derived from plant sources play an important role in the stemflow acidity. Our results suggested that the strong stemflow acidity in Japanese cedar was derived from an internal biological characteristic rather than influences of external acidic deposition.

Sprout initiation and growth for three years after cutting in an abandoned secondary forest in Kyoto, Japan

Secondary forests in Japan have been abandoned and the ecosystem has degraded since the high economic growth period. We carried out cutting in January in three small areas of a long-abandoned secondary forest and investigated the sprout initiation and growth of woody plants for three years in order to reveal the early stage of sprout regeneration and to understand the sprouting ability and characteristics of each species for effective management. The percentage of sprouted stumps and the number of sprouting shoots was substantially maximized in autumn in the first year. These results suggest that autumn monitoring in the first year after cutting shows the maximum percentage of sprouted stumps and the maximum sprout number when cutting was conducted in the dormant season. With regards to species characteristics, Eurya japonica showed a low percentage of sprouted stumps in the lower plot, where the mean diameter at breast height for this species was smaller than in the other plots. The sprouting ability of E. japonica was deemed to be influenced by parent tree size. Ilex pedunculosa and Lyonia ovalifolia var. elliptica had high percentages of sprouted stumps and many sprouts. These species are useful for obtaining sprouting shoots (e.g., for firewood), but it is difficult to control their sprouting.