Nitrogen retention in Japanese cedar stands in northern Honshu, with high nitrogen deposition

摘要

High nitrogen, especially ammonium, input has been observed in Shichinohe, Aomori Prefecture, northeastern Japan. A monitoring study on precipitation, throughfall, and stream water has been carried out to estimate the stage of nitrogen saturation since 1996. Fifty-two to 70 % of nitrogen input in throughfall was retained in forest ecosystems. Nitrate concentration in stream water tended to decree throughout the study. There was no symptom of nitrogen saturation at Japanese cedar stands in Shichinohe, although high nitrogen input in open bulk has been observed. Ammonium (NH{sub}4{sup}+) was retained in the canopy. The ratio of NH{sub}4{sup}+ input in throughfall to that by open bulk was 0.40- 0A7. Total inorganic nitrogen input under the canopy amounted 0.68-0.72 lernoic ha{sup}(-1)yr{sup}(-1) (9.6 - 10.0 kg N ha{sup}(-1)yr{sup}(-1)). Our results suggests that atmospheric nitrogen input has benefited the tree growth.