1. ; Department of Biology, Faculty of Science; Tokyo Metropolitan University; Minamiohsawa 1-1 Hachiohji, Tokyo 192-03 Japan
2. ; Department of Biology; National Institute of Polar Research; 9-10 Kaga-1, Itabashi-ku Tokyo 173 Japan
3. ; Glabal Agro-environment Research Team; National Institute of Agro-environmental Sciences; Tsukuba, Ibaraki 305 Japan
4. ; Division of Plant Ecology; National Institute of Agro-environmental Sciences; Tsukuba, Ibaraki 305 Japan