采用树木年轮和稳定同位素技术,分析了2000—2015年生态输水对塔里木河下游胡杨树木轮宽指数和树轮稳定碳同位素比率（δ¹³C）的影响,探讨了生态输水与胡杨生长的关系。研究结果表明：（1） 胡杨生长与生态输水量有着密切关系。受生态输水影响,塔里木河下游上段英苏断面胡杨轮宽指数和树轮δ¹³C经历了3个阶段：在最初前4 a（2000—2003年）的输水过程中,胡杨生长响应十分敏感,胡杨轮宽指数和树轮δ¹³C呈增加趋势,其平均值分别为1.52和-26.70‰;但在2004—2009年,随着生态输水量的逐渐减少,胡杨轮宽指数和树轮δ¹³C逐渐下降,分别较2000—2003年平均减少了28.83%和2.41%;当2010—2015年生态输水重新稳定后,胡杨轮宽指数和树轮δ¹³C也逐渐增加并趋于稳定。（2） 输水时间与胡杨生长有着密切关系。胡杨生长与生长年（前一年9月—当年8月）、生长季（4—8月）和前一生长年（前一年4月—当年3月）生态输水相关性最高,与自然年（1—12月）生态输水相关性不显著。其中,2008年自然年（1—12月）没有下泄生态水,2009年（1—12月）虽然有输水,但因2009年生长季、生长年和前一生长年均没有生态水补给,导致胡杨轮宽指数和树轮δ¹³C在2009年降至2000—2015年的最低值,分别为0.76和-27.50‰,较2003年分别降低了61.18%和3.14%。（3） 根据研究结果,推导出生态输水促进胡杨生长的作用机理：塔里木河下游的生态输水有效抬升了地下水位,改善了胡杨生长的水分环境,提升了胡杨水分利用效率,从而增加光合累积产物,最终促进了树木的生长。但生态输水对地下水埋深、胡杨生长的影响具有滞后效应,滞后时间约为1 a。为维持荒漠河岸林的有效恢复与重建,建议塔里木河下游生态输水最好在植物生长季实施。

Water is a decisive factor limiting plant growth and development in extremely arid areas. Although numerous studies on the relationship between water resources and plants in the lower reaches of Tarim River, Xinjiang, China have been published, most of them focused on short time changes in the physiological or biochemical characteristics of individual plants, plant diversity, or normalized differential vegetation index. Thus, the relationship between long-term plant growth characteristics and water resources must be examined further. In this study, the responses of the long-term growth characteristics of Populus euphratica to ecological water conveyance from 2000 to 2015 in the lower reaches of Tarim River were analyzed using the tree-ring width chronology and stable carbon isotope (δ ¹³C) characteristics of the species. Results showed that: (1) P. euphratica growth was significantly related to the amount of ecological water conveyance, and the tree-ring width chronology and δ ¹³C values of P. euphratica in Yingsu indicated three stages. Specifically, tree growth was very sensitive to ecological water conveyance in 2000—2003, and the main tree-ring width chronology and δ ¹³C values of P. euphratica in this period were 1.52 and -26.70‰, respectively. When ecological water conveyance was reduced in 2004—2009, the mean tree-ring width chronology and δ ¹³C values of the species decreased by 28.83% and 2.41%, respectively. The values of these indices remained stable when the ecological water conveyance amount was increased and maintained in 2010—2015. (2) P. euphratica growth was closely related to the ecological water conveyance time, especially in terms of growth year (from previous September to current August), growth season (from April to August), and previous growth year (from previous April to current March). However, plant growth was not significantly related to ecological water conveyance of the calendar year (from January to December). Because no ecological water conveyance was conducted in the growth season, growth year, and previous growth year of 2009 or in the growth seasons of 2006—2009, the tree-ring width chronology and δ¹³C values of P. euphratica of 2009 were lowest in 2000—2015. The tree-ring-width chronology and δ ¹³C values of P. euphratica in 2009 decreased by 61.18% and 3.14% compared with those in 2003, respectively. (3) Ecological water conveyance decreased the groundwater depth and improved the water environment of P. euphratica, thereby enhancing the water use efficiency, accumulated photosynthetic production, and growth of the trees. However, a 1-year lag effect between ecological water conveyance, groundwater depth, and P. euphratica growth was also observed. Therefore, ecological water conveyance should be implemented during the plant growth period in the lower reaches of Tarim River to restore and reconstruct the desert riparian forest effectively.