Sun Shou Jia, Li Chun You, He Chun Xia, Zhang Jin Song, Meng Ping
Key Laboratory of Tree Breeding and Cultivation of State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China.
Collaborative Innovation Center of Sustaintable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China.
Ying Yong Sheng Tai Xue Bao. 2017 Jul 18;28(7):2119-2127. doi: 10.13287/j.1001-9332.201707.024.
The Three-North Shelter Forest is an important ecological defense of Beijing-Tianjin-Hebei area. About four-fifths of poplar plantations declined and about a third of them were dying or already dead in the last ten years. The mortality of trees resulted in the decline of ecological function of poplar plantation. In this study, we investigated the differences of δC and intrinsic water-use efficiency (WUE) values in the tree-ring between dieback and non-dieback trees with stable carbon isotope method. The cause of poplar plantation degradation and mortality was retrospectively ana-lyzed. The results showed that the diameter of poplar trees of nearly the same age decreased with the increase of degradation degree. The δC value of rings from dieback trees varied between -25.26‰ and -22.97‰, whereas that of non-dieback ones was -26.15‰ to -23.50‰. The δC values of dieback trees were higher than that of non-dieback ones from 1997. There was a nonsignificant difference of the WUE between dieback and non-dieback tree-ring from 1997 to 2001. And the difference of WUE between dieback and non-dieback tree was significant since 2002. The continuous occurrence of positive ΔWUE(WUE-WUE) values might be one of important factors for subsequent divergence of the dieback and non-dieback poplar trees. The WUE of both dieback and non-dieback trees had no significant relationship to precipitation, relative humidity and ET, while significantly related with air temperature and ground water depth. The retrospective ana-lysis results showed that extreme drought in 1997 was a threshold when poplar trees began to decline. The underground water was overused because of land use change, which increased the intensity and duration of the drought, thus accelerated the degradation and mortality of poplar trees.
三北防护林是京津冀地区重要的生态屏障。在过去十年中，约五分之四的杨树人工林出现衰退，其中约三分之一正在死亡或已经死亡。树木死亡导致杨树人工林生态功能下降。本研究采用稳定碳同位素方法，调查了衰退树木和未衰退树木年轮中δC和内在水分利用效率（WUE）值的差异。对杨树人工林退化和死亡的原因进行了回顾性分析。结果表明，同龄杨树的胸径随退化程度的增加而减小。衰退树木年轮的δC值在-25.26‰至-22.97‰之间，而未衰退树木的δC值在-26.15‰至-23.50‰之间。自1997年以来，衰退树木的δC值高于未衰退树木。1997年至2001年，衰退树木和未衰退树木年轮的WUE差异不显著。自2002年以来，衰退树木和未衰退树木的WUE差异显著。ΔWUE（WUE-WUE）值持续为正可能是衰退杨树和未衰退杨树后续分化的重要因素之一。衰退树木和未衰退树木的WUE与降水量、相对湿度和ET均无显著关系，而与气温和地下水位显著相关。回顾性分析结果表明，1997年的极端干旱是杨树开始衰退的一个阈值。土地利用变化导致地下水过度开采，增加了干旱的强度和持续时间，从而加速了杨树的退化和死亡。
