College of Resources and Environment;
Southwest University;
Chongqing 400716;
P.R.China;
College of Geography Science;
Chongqing Normal University;
Chongqing 400047;
P.R.China;
Institute of Resource;
Ecosystem and Environment of Agriculture;
Nanjing Agricultural University;
Nanjing 210095;
P.R.China;
Graduate School of Agriculture;
Hokkaido University;
Sapporo 060-8589;
Japan;