Age-related modulation of the nitrogen resorption efficiency response to growth requirements and soil nitrogen availability in a temperate pine plantation - Sun, Zhenzhong (Beijing da xue. College of Urban and Environmental Sciences. Department of Ecology) ; Liu, Lingli (Zhongguo ke xue yuan. Institute of Botany) ; Peng, Shushi (Beijing da xue. College of Urban and Environmental Sciences. Department of Ecology) ; Peñuelas, Josep (Centre de Recerca Ecològica i d'Aplicacions Forestals) ; Zeng, Hui (Peking University Shenzhen Graduate School) ; Piao, Shilong (Beijing da xue. College of Urban and Environmental Sciences. Department of Ecology)