1. State Key Laboratory of Soil and Sustainable Agriculture; Institute of Soil Science, Chinese Academy of Sciences; Nanjing 210008 P.R. China
2. College of Environmental Science and Engineering, Guilin Univ. of Technology; Guilin 541006 P.R. China
3. The Univ. of Tokyo; 1-1-Yayoi Bunkyo-ku Tokyo 113-8657 Japan