Recent shift from dominant nitrogen to CO2 fertilization control on the growth of mature Qinghai spruce in China's Qilian Mountains - Wang, Ziyi (Shaanxi Normal University. School of Geography and Tourism) ; Liu, Xiaohong (Shaanxi Normal University. School of Geography and Tourism) ; Peñuelas, Josep (Centre de Recerca Ecològica i d'Aplicacions Forestals) ; Camarero, Jesús Julio (Instituto Pirenaico de Ecología) ; Zeng, Xiaomin (Shaanxi Normal University. School of Geography and Tourism) ; Liu, Xueyan (Tianjin University. School of Earth System Science) ; Zhao, Liangju (Northwest University. College of Urban and Environmental Sciences. Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity) ; Xu, Guobao (Northwest University. College of Urban and Environmental Sciences. Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity) ; Wang, Lixin (Indiana University-Purdue University Indianapolis. Department of Earth Sciences)