【作者】 刘普幸；

【导师】 陈发虎；

【作者基本信息】 兰州大学 ， 自然地理学， 2007， 博士

【摘要】 黑河下游与蒙古相毗邻的额济纳旗，历史上曾是丝绸之路北路的咽喉要道，曾孕育过极其重要的汉代文明、西夏和元代文明。严酷的自然环境，极端脆弱的生态系统，特别是20世纪80年代以来额济纳绿洲萎缩、天然植被衰败，生物多样性减少、尾闾湖泊干涸、地下水位下降、土壤次生盐渍化和土地荒漠化日益加剧，演变为我国沙尘暴的策源地之一。恶化的生态环境已成为世人关注的焦点。拯救额济纳绿洲生态环境不仅有利于维护区域社会经济持续发展、保护区内生物多样性，维持生态平衡，而且对于维护我国西北、华北等地的生态安全、维护黑河全流域绿洲的生存与完整性具有举足轻重的作用。深入认识该地区的水文气候变化过程及其规律，理解和认识过去水文-气候-生态的变化，解释人类的、生态的和自然的现象，成为亟待解决的科学课题。胡杨(Populus euphratica，Oliv．)为杨柳科(Salicaceae)杨属(Populus)，依靠潜水或河水灌溉生长。它是亚洲中部荒漠区分布最广的乔木树种之一，也是额济纳旗惟一的河岸乔木和优势种，具有防风固沙、维护脆弱生态平衡的功能，也是生态环境变化的指示器。额济纳旗胡杨林是目前全球仅存面积最大的三大天然胡杨林分布区之一，在该区域开展胡杨研究具有重要的科学价值和现实意义。树木年轮是气候变化的自然记录者，具有定年准确、连续性强、分辨率达年甚至季的高精度、地域分布广泛、取样容易等优势，其理论与方法已被广泛应用于气候、水文、生态、考古、火山等研究领域，已成为反映干旱区水文生态逐年变化，重建环境演变历史的最重要方法之一。本文以额济纳旗河岸胡杨林为研究对象，应用树轮水文气候学理论和方法，研究了额济纳旗树木年轮的水文-气候响应模式与机制，主要工作和结论包括：1．沿额济纳东河、西河自上游向下游6个采样点采集287根胡杨树芯，经过固定、打磨、交叉定年、量测和COFECHA软件进行定年质量检验后，按照树木年轮学规范步骤与程序，分别建立了各采样点标准化年表(STD)、差值年表(RES)和自回归年表(ARS)三种树轮宽度年表，年表时间序列最长156年，最短87年，平均112年。利用PCA方法提取了代表区域树木共同生长特征的第一主成分年表(PC1)。树轮宽度年表的质量指标、聚类分析和PC1权重值分析表明，研究区6个采样点树轮宽度年表有明显的空间变化特征。2．将6个采样点年表及其第一主成分(简称6PC1)年轮宽度序列分别与额济纳旗气象站4个气候要素、黑河下游正义峡水文站水文实测资料进行相关普查，结果显示胡杨年轮生长与正义峡径流量(1954-1999)之间主要表现为负相关关系，与气温(1960-2001)之间存在正相关关系，与降水量(1960-2001)却无多大关系。但各胡杨年轮宽度年表所包含水文气候信息量不同，对水文要素的响应具有明显的沿上、中、下游滞后一个月的空间差异，并与径流量补给地下水位出现的最浅月份时间相一致，反映了地下水是直接影响额济纳旗胡杨生长的主要水文限制因子；正义峡径流量通过影响地下潜水位变化间接影响胡杨生长，胡杨径向生长对水文要素的响应具有明显的时空差异。6个年表对气候要素的响应一致性较好。利用6PC1年轮宽度序列进行相关函数分析后，相关关系显著增强，反映PC1年轮指数对区域水文气候的共同响应要强于单个年表。3．除LX年表外，研究区胡杨生长与正义峡径流量主要呈负相关关系，6个采样点年表和6PC1年表均与2-4月径流量的负相关最显著，并以6PC1的响应更显著，相关系数为-0.544(p≤0.05)。由于各个采样点附近的地下水位在2-4月是一年中最浅的时期(其中3、4月分别为最浅月份)，上、中、下游采样点所对应地下水位分别为2.45m、1.6m、3.55m；无论对胡杨休眠期的2月、3月，还是对开始进入生长期4月的胡杨而言，地下水都已满足胡杨生长水分需求，而2-4月径流量较大，占年径流量的25.8％，径流补给只能使地下水位过高，造成胡杨生长受到胁迫。LX采样点年表与2-4月径流量负相关关系不显著，而与6-8月的径流量呈显著正相关关系，可以理解为6-8月是胡杨生长旺季，蒸发最强烈，尽管LX采样点地下水位较浅，但海拔相对最高，径流量补给少，又经历了一年中4-6月径流量最少时期，对地下水补给量微不足道，土壤层水分散失强烈，胡杨生长可利用的水分急剧减少，所以与6-8月径流量呈显著正相关关系，并具有生物学意义。各采样点地下水位浅是研究区胡杨轮宽序列与径流量呈负相关的真正缘由。同时也反映了胡杨径向生长对水文因子响应的时空差异性既受水文因子限制，又与海拔等小地形状况关系密切。4．胡杨径向生长对气候要素响应的分析发现，额济纳旗胡杨主要依赖地下水生长，在水分充足情况下，胡杨生长主要受温度因子限制，与降水量无关，这与新疆塔里木河胡杨研究结论相一致。相关时段分析结果显示，6个采样点年表中的5个年表及6PC1年轮序列均与2-3月平均气温、冬季(12-2月)平均最低气温正相关最显著，都超过95％信度水平，与最高气温最显著的响应在9-11月的秋季，但对当年胡杨生长无多大生理学意义。反映出最低气温对胡杨生长的影响远比最高气温更有意义。其中，6PC1年轮序列与2-3月平均气温、12-2月平均最低气温最显著的相关系数分别为0.472和0.460(p≤0.05)。从生理学角度可解释为：由于2-3月胡杨处在休眠期，不需要过多水分，而该时期研究区地下水位很浅，径流量比较大，胡杨生长的土壤水分积累过多，胡杨年轮生长与径流量呈显著负相关关系，因此，2-3月较高的气温能增加年蒸发能力，利于过湿土壤层水分的散失，增强树木呼吸作用。与冬季(12-2月)平均最低气温相关最显著也可以理解为：一方面冬季和休眠期树木的形成层虽然停止活动，但仍可通过光合作用合成有机物储存于胡杨细胞内，有利于次年树木生长；另一方面，研究区胡杨树木受到最低气温胁迫，尽管冬季树木已停止生长，但冬季、前一年10月至当年3月径流量均为一年中最多时期，土壤水分累积使土壤湿度大，该时段最低气温过低可能会加剧冻土层中树木根系因反复冻融造成断根、错位等机械伤害从而影响下一年年轮生长。更多还原

【Abstract】 Ejin Banner in the lower reaches of the Heihe River, Inner Mongolia, Arid China was an vital passage of the North Silk Road in ancient times, and the cradle of civilization of Han Dynasty, Xixia Dynasty and Yuan Dynasty. Bordering upon Mongolia to the north and being important strategically, Ejin Banner, a stockbreeding region where many people from different minorities inhabit, is an important ecological county in Northern China.The natural environment is adverse and the ecosystem is extremely feeble in Ejin Banner. With the rapid growth in population and the development of irrigated farming in the middle reaches of Heihe River since 1980, the ecological environment has been increasingly deteriorated, for example, shrunken Ejin Oasis, degenerate natural vegetation, reduced biodiversity, drying Juyan Lake, declining groundwater levels, saline-alkali soil and so on. As a result, the region has turned into a cradle-land of sandstorms in China, which became an issue of universal concern. Restoring the eco-environment of the Ejin Oasis will not simply promote Sustainable development of regional economy, protect biodiversity and maintain ecological balance within the region, but play an important role in preserving ecological security in Northwest and Northern China, and in keeping the survival and integrity of oasis along Heihe River. Therefore, it seems particularly significant to have a deep insight into the process and regularity of hydroclimate changes and a thorough understanding of hydrological-climatic-ecological changes in the past, and make an interpretation of human, ecological and natural phenomenon. It is exactly a scientific subject crying out for solutions. Populus euphratica Oliv., Populus of Saliceae, one of the most widespread species in desert regions of the Middle Asia, is not merely a single arbor, a dominant species of the vegetation in Ejin oasis, and an indicator of eco-environmental degeneration, but also a natural barrier of preventing wind, fixing sand and maintaining fragile ecological balance. Now Populus euphratica in Ejin Banner is one of three major survival natural distribution zones of the world. It is of great practical significance and scientific value to study on Populus euphratica in the region.Tree-ring is the natural records of climate changes, which has many advantages, for instance, cross-dating accuracy, intense continuity, high-resolution, wide geographical distribution, easy sampling. Its theory and method have already widely used in such fields as climate, hydrology, ecology and archeology, volcanoes and so on. Recently, it has become one of the most important approaches reflecting the history of hydrological and ecological changes and reconstruction environmental evolvement in arid regions.In the thesis, we study on the responses model of radial growth of Populus euphratica species to hydroclimatic factors from tree-ring of Populus euphratica in Ejin Banner based on the theories and methods of dendrochrology. Our conclusions are as follows.1. Tree-ring samples were collected separately along the Ejin River, Northwest China, for studying the relationship between radial growth of Populus euphratica species and climatic factors. There are 287 tree-ring increment cores were retrieved from 6 sampling sites, and then they were mounted, sanded, cross-dated with skeleton plot and measured to the nearest 0.001mm with standard techniques. The quality of tree sequences was checked with the software COFECHA. Totally 18 chronologies were developed with ARSTAN program and were classified as three types, STD, RES and ARS by different detrending methods. The longest chronology series is 156 years, the shortest 87 and the average112. Then the first PC representing the greatest proportion of the total variance is gained by Principal component analysis (PCA), which is used to summarize the regional variation in radial growth patterns carried by the six site chronologies with the software PCA. The analysis results of the quality indexes of chronologies, cluster analysis and the weights of the first Principal Component (PC1) indicate that the tree ring-width chronologies at six sites is characterized by the apparent spatial change. Compared with the PC1 of 6 sites and 3 good sites, the PC1 at three sites is better.2. By correlation function and response function, the responses of radial growth of each chronology, the six chronologies and 6PC1 to 4 climatic factors of Ejin weather station and the runoff of Zhengyixia hydrological station were analyzed. The results show that the correlation between ring-width and the Zhengyixia runoff is mainly negative, the correlation between ring-width and the temperature is mainly positive in the area studied and the radial growth of trees have nothing to do with the precipitation. But the information quantity in tree ring-width chronology at every site is totally different. Radial growth of Populus euphratica assumes obvious spatial difference in the upper, middle and lower reaches of the Ejin River and is consistent with the time of the occurrence of the shallowest depth of the level of groundwater recharge. It proves that the groundwater is the main limiting factor, both direct and indirect, of the runoff by supplying with the groundwater.The hydrological factor responding to the radial growth has an obvious difference in space-time. The more obvious the correlation of ring-width of 6PC1 to hydro-climatic factors is, the more intense responses of ring-width of 6PC1 to hydro-climatic factors are. It proves that the response of the 6PC1 to the district hydrological factor is stronger than that of the single chronology.3. Except for LX chronology, the ring-width of tree is mainly correlated negatively with Zhengyixia runoff, and the negative correlation between ring-width at six sites and 6PC1 and February-April Zhengyixia runoff is more apparent, whose correlation coefficient is -0.544 (p≤0.05) respectively. It has a physiological significance. Because the all-year depth of groundwater is shallow in the area studied and the shallowest is in February-April with 2.45m、1.6m、3.55m. Not only in the rest period of February and March but also in growth period of April, has the groundwater met water demand of the growth of Populus euphratica. The over shallow groundwater supplied by runoff intimidates the growth. So the groundwater is a direct hydrological factor of affecting the radial growth of Populus euphratica. Zhengyixia runoff indirectly affects the radial growth of Populus euphratica by changes of the depth of the groundwater. The main correlation between LX chronology and Zhengyixia runoff is positive in June-August which can be explained as the time for growing and flourishing of Populus euphratica and for evaporating most severely. Though the underground level at LX site is relatively shallow, the relative elevation is the tallest, the runoff replenishment is little, and then experiences the period of minimal runoff during April-June of a year, so it is insignificant to the amount of replenishment of the groundwater. The soil layer humidity loses so greatly that the moisture the growth of Populus euphratica can make use of reduces rapidly. Therefore, the correlation between LX chronology with Zhengyixia runoff is positive in June-July. The shallow depth of groundwater is the real reason of the negative correlation between ring-width of the tree and Zhengyixia runoff. It also reflects the time space difference in responses of radial growth of Populus euphratica to the hydrology factor is limited by the hydrology factor and closely related to such small geography conditions as elevation.4. The response analyses of radial growth of Populus euphratica to climate factors reveal that the growth of Populus euphratica mainly relies on the underground water. While the water is sufficient, the growth of Populus euphratica is mostly confined by temperature factor and has nothing with the precipitation. The conclusion is consistent with that of Xinjiang’s research. According to the analytic results of related periods, it is the most apparent that ring-width at the five of six chronologies and 6PC1 is correlated positively with the average temperature from February to March and that in winter(from December to February), all beyond 95% coefficient level The most obvious response to the maximum temperature is in autumn(from September to November) , while it has very little biological significance in the growth of Populus euphratica in those years. It suggests that the minimum temperature has a more significant influence on the growth of Populus euphratica than the maximum.The coefficient related to the connection between 6PC1 and average temperature from February till March and from December to February are 0.472 and 0.460(p≤0.05). Physiologically speaking, during the rest period for Populus euphratica from February to March, the demand for water is little; meanwhile the groundwater level in the region studied is shallow, so that the soil accumulates too much moisture, which proves that the relation between the ring-width of tree and runoff is mainly negative.The relatively higher temperature can improve the capacity to vaporize, benefit for the loss of soil moisture and strengthen the respiration of plants. The close relation with the minimum temperature in winter can be interpreted as the following points. On one hand, though the activities of cambium of trees in the rest period in winter come to a halt, they can synthesize organism by photosynthesis to store it in Populus euphratica cells. It is in favor of the growth of trees in next year. On the other hand, Populus euphratica in the region studied is menaced by the minimum temperature. Hence, although the trees stop growing in winter, the runoff from the October of the preceding year to the March of the year is the maximum of the whole year, the accumulation of the soil moisture results in an increase in humidity. If the minimum temperature in this period is too low, some mechanical damages, such as root broken and root displacement, thus influencing the growth of tree ring, is likely to get more severe in the following year.更多还原