Zhanjiang Normal University;
Zhanjiang 524048;
P.R.China;
Center for Chinese Agricultural Policy;
the Chinese Academy of Sciences;
Beijing 100101;
China;
Institute of Geographical Sciences and Natural Resources Research;
the Chinese Academy of Sciences;
Beijing 100101;
P.R.China;
Graduate School;
the Chinese Academy of Sciences;
Beijing 100094;
P.R.China;
Institute of Crop Sciences;
Chinese Academy of Agricultural Sciences;
Beijing 100081;
P.R.China;