塔里木河下游胡杨树轮宽度和密度对水分响应的研究

Tarim River is the longest inland river in China. It is also characterized by abundant natural resource and weak environment condition, the contradiction of the regional water resource is most prominent in China and even in the entire world. Populus euphratica plays a very important role in maintaining ecosystem function the Tarim River. The degrading sequences of species were related to their physiological and ecological characteristics, especially their sensitivity to changes of water condition. Given the accuracy of tree-rings data for recording variations in growth conditions and the ability to use these variations to reconstruct long-term groundwater data, we analyzed the changes in the tree-ring width/tree-ring density of P. euphratica in the lower reaches of the Tarim River. The relationships between tree-ring width/tree ring density and surface runoff are analyzed as well. Base on the analysis above, this project will find the variations in growth conditions of P. euphratica following the different water condition from temporal and spatial scale and establish a response function to reveal the mechanism of P. euphratica physiological responses to different water condition. The results will provide reference for the sustainable use of water resources and ecological environment protection in the lower reaches of the Tarim River. The multiple tree-ring indexes study in this project will enhance the regional P. euphratica researches.

塔里木河流域是我国干旱区受人类干扰影响、生态系统受损最为严重的区域之一，其人为干预条件下的生态恢复在世界范围内具有典型性。胡杨作为塔里木河流域荒漠河岸林的优势种和建群种，其分布及其演化是流域整体生态健康状况的重要表征。本研究拟在申请人已取得的塔里木河下游胡杨树轮与生态恢复的研究成果基础上，以塔里木河下游不同退化程度的四个典型断面的胡杨为研究对象，选取树轮宽度和密度指标，建立树轮年表，明晰塔里木河下游胡杨树轮宽度、密度年表的变化特点及其环境意义，研究胡杨生长的时空分布特征；结合塔里木河下游水文资料，综合分析胡杨树轮宽度和密度对地下水水位和地表径流量的响应规律；构建胡杨生长与水分条件的响应函数，分析地表径流和地下水动态变化与胡杨树轮宽度和密度的内在联系，揭示多胡杨树轮参数对水分变化的响应机理。为丰富塔里木河下游胡杨林的保护和水资源开发利用、区域生态环境修复与重建的理论提供科学依据。

树木生长受环境因子的制约，它在应对环境变化的过程中形成了良好的反馈机制，以提高自身抵御外界胁迫的能力。树木年轮作为一种环境信息的载体，同样对环境变化反应敏感。本研究选取荒漠河岸林的建群种胡杨为研究对象，以塔里木河下游为典型靶区，以河道断流和生态输水两大环境突变事件为研究背景，探讨胡杨树轮生长对水分动态变化的时空响应规律，揭示了环境突变和中度干旱胁迫对胡杨生长影响的过程和机理。具体研究结果如下：.1）塔里木河下游胡杨林的空间分布在河道垂直方向上表现为明显地受河道影响的特点，而沿河道方向则表现为分布的不连续和明显的空间差异性，分布格局总体上呈现出种群聚集分布的特点；.2）在塔里木河下游，地下水埋深的变幅与生态输水的水量和持续时间关系密切；相对于河道断流，生态输水促使胡杨标准年表序列增加了8.7%。随着地下水埋深的增加，胡杨在受到中度干旱胁迫（即中度胁迫）期间，它的生理调节能力不断增强，进而驱动了树轮标准年表序列由下降转变为上升趋势，因此胡杨生长对干旱胁迫呈现负反馈，这有利于稳定胡杨林的群落结构。.3）温度对胡杨影响的时间段不同：在塔里木河上游和中游采样点，胡杨生长分别受5-10月、6-10月温度的影响。但塔里木河上游和中游适宜胡杨生长的温度范围略有不同。上游采样断面，适宜胡杨生长的温度范围为21.1-21.3℃；中游采样断面，适宜胡杨生长的温度范围为21.4-21.9℃。.本研究从生理角度剖析了中度干旱胁迫导致胡杨树轮生长发生分异的机理，提出并验证了中度干旱胁迫诱发树木产生负反馈调节的科学假设，打破了树轮重建所遵循的“均一化”理论，为进一步提升树轮水文重建技术和推进生态水优化调度奠定了基础。