Effect of growing season degree days on gross primary productivity and its variation characteristics in alpine shrubland at the southern foot of Qilian mountains

• ZHU Jingbin, 
• HE Huidan, 
• LI Hongqin, 
• ZHANG Fawei, 
• LI Yingnian, 
• YANG Yongsheng, 
• ZHANG Guangru, 
• WANG Chunyu, 
• LUO Fanglin