State Key Laboratory of Crop Biology College of Agronomy Shandong Agricultural University Tai''an 271018 Shandong China;
College of Life Sciences Shandong Agricultural University Tai''an 271018 Shandong China;
Jiasixie Agronomy College of Weifang University of Science and Technology Shouguang 262700 Shandong China;
high nitrogen; HN; maintain photosynthetic;