1. College of Resource and Environmental Science, Jilin Agricultural Univ., Changchun 130118.
2. Associate Professor, College of Resource and Environmental Science, Jilin Agricultural Univ., Changchun 130118 (corresponding author).
3. Dept. of Plant, Soil and Microbial Sciences, Michigan State Univ., East Lansing 48824.
4. Professor, College of Resource and Environmental Science, Jilin Agricultural Univ., Changchun 130118.