1. Inst. of Botany of The Czech Academy of Sciences Zámek 1 CZ‐25243 ůhonice Czech Republic
2. Faculty of Science, Dept of Botany, Univ. of South Bohemia České Budějovice Czech Republic
3. Forest Research Station, Field Science Center for Northern Biosphere, Hokkaido Univ. Nayoro Japan
4. Dept of Biology, Faculty of Science, Shinshu University Matsumoto Japan
5. Inst. of Low Temperature Science, Hokkaido Univ. Sapporo Japan