【作者】 龙翔；

【导师】 周爱国； 孙自永；

【作者基本信息】 中国地质大学 ， 生态地质学， 2014， 博士

【摘要】 水是影响干旱区生态系统稳定最重要的因子,区内水文循环主导着生态过程。干旱区地表水资源分布极端不均,绝大多数的地表水都集中在少数内陆河中,使内陆河沿岸成为绿洲的主要分布区,在内陆河沿岸,距河道越远,空气相对湿度降低,河水-地下水作用强度越弱,地下水埋藏越深,土壤水分含量减小,形成了一个天然的水分梯度带,即离河道距离越大,可利用水分越少。受这一水分梯度带的控制,垂直河道方向上常形成了河岸带生态系统、绿洲生态系统和荒漠生态系统的分带。受气候变化和人类活动的影响,干旱区原有的水文节律正在改变,引发了与生态用水之间的矛盾,造成了荒漠生态系统的扩张以及河岸、绿洲生态系统的退化,严重制约着内陆干旱区经济的可持续发展。为实现我国西北干早区社会经济的可持续发展,必须对水资源进行合理的利用,其中的关键是生态用水配置方案的确定。植被是生态用水的对象,如何保证这些生态用水能被植物有效利用,取决于放水方式与植物的水分利用方式是否契合,只有准确辨识不同生态系统中的植被所需水分的来源(降雨、河水、地下水、土壤水等)、需水的时间分布特征以及同一生态系统中不同物种间水分利用和竞争关系,才能保证生态用水配置方案的科学有效。同时,植物如何利用有限的水分,以及在水分变化下产生何种响应等问题的研究对维护生态系统的稳定具有重要意义。基于以上背景,本研究以内陆干旱区黑河中游地区河岸带为研究对象,利用稳定同位素、Dynamax热平衡法方法对研究区内优势植物——柽柳灌木林的水分来源、蒸腾耗水、和水分利用效率等水分生理特征及变化规律进行分析,同时结合河水、地下水、土壤水与降水等动态变化,探讨了黑河中游地区河岸带植被对水文过程的水分生理响应机制。主要研究结果如下：1.河岸带水文过程及D、18O同位素特征研究区具有降水稀少且分布集中的特点：降雨一般发生在每年的6-9月,期间黑河水位和观测点地下水位波动较频繁；因包气带土壤前期含水量、降雨的年内分配不均和雨季历时长短不同,河水与地下水呈现出不同动态变化。旱季地下水位波动平缓；雨季受人工调蓄作用、河水侧向补给综合影响,河流和地下水原有节理被改变,地下水随河水涨跌而波动,并具有滞后效应。空间上,2个观测点因距河远近不同,横向上渗透流速受渗流途径长短影响较大,含水介质类型存在差异性,这些因素综合作用,导致地下水位对河水位变化的响应在垂直于河道方向存在梯度变化。研究区的大气降水线方程为δD=8.01δ18O+1.51(r2=0.94, n=136),截距小于全球大气降水线,研究区氘盈余d变化表现为冬半年较高,夏半年较低；降雨的δD、δ18O值具有明显的季节性变化：其中,雨季降雨的同位素组成大部分落在LMWL上,其δD-δ18O关系线与LMWL接近,略低于GMWL,表明其水汽来源于海洋,属于季风性降雨；旱季降雨的同位素组成落在LMWL的偏左上方,其δD-δ18O关系线的斜率远远低于LMWL和GMWL,截距则远大于LMWL,除表明降雨过程中经历了蒸发富集效应外,还表明其水汽可能源于当地地表水与地下水的蒸发及植物叶片的蒸腾。研究区河水以祁连山区降水来源补给为主,但河流径流中同位素含量的分布普遍高于同期的山区和出山口,则是由于在中游地区不但有降水与回灌水对同位素的影响,而且随着河流流程的延长,强烈的水体蒸发也导致了同位素含量相对增高。地下水在两年的观测期内均保持稳定并相对于降雨、河水偏贫,受降雨和回灌影响较小,其来源主要为祁连山区的降雨和冰雪融水。两个观测点由于不同土壤质地条件,土壤含水率呈现明显差异,降雨对25cm以下士壤水分影响有限；不同层次土壤水分布具有明显差异；十壤水样品的同位素的变化具有定的规律性,其平均值整体随土壤深度的增加而减小,深层土壤在长时间尺度上保持相对稳定并随深度逐渐接近地下水,而上层土壤则受环境因子影响较大变现为偏正的蒸发富集特征,土壤水分的变化主要受控于地下水位的波动。2.河岸柽柳对地下水的依赖通过对比植物茎干水和不同深度土壤水的δ18O值发现：黑河中游河岸柽柳在其生长季内的吸水层位随地下水位波动而产生季节变化,对于NO.1观测点,当地下水位较低时,主要吸收15-35cm范围的土壤水,而当地下水处于持续高水位时主要利用60cm以下土壤水,柽柳的根系形态可塑性强,可以适应不同基质的土壤含水量变化。而NO.2观测点柽柳在生长期内均吸收15-35cm范围的十壤水；生长期内柽柳主要水分来源为由地下水补给的土壤水,基本不利用降水与河水。河岸带河水频繁地通过与地下水的相互作用影响柽柳生境的水分条件,间接决定了吸水层位的变化与不同时期的水分利用策略。3.河岸柽柳水分利用效率特征利用稳定同位素13C研究了两个观测点柽柳的水分利用效率,研究结果显示：2011年观测期内,在地下水位降低的时期,随着吸水层位土壤的水分消耗,两个观测点的样柳在水分亏缺胁迫下均表现出水分利用效率升高的趋势；当地下水上涨时,土壤水得到了补充,此时,水分利用效率有所降低降低。而在观测期后半段,地下水长时间保持较高水位,植物根系由于土壤淹水而限制了植物根的呼吸从而造成淹水胁迫,造成植物根际O2浓度而形成了低氧和无氧状态,影响了植物正常生理代谢和生长发育,使得叶片和叶面积减少,减少蒸腾失水强度,形成了较低的水分利用效率。4.河岸柽柳蒸腾耗水变化特征样柳液流速率日变化呈明显的多峰格型的宽峰曲线,中午存在“午休”现象；全天树干液流速率变化可以划分为：液流迅速上升、液流相对稳定、液流迅速下降和夜间液流四个阶段。影响柽柳液流速率日变化的环境因子有太阳辐射、空气温度、大气相对湿度、十壤含水量和风速。柽柳具有夜间水分补偿现象,夜间仍然存在着树干液流变化,与白大树干液流相比,变化比较平缓,波动较少,液流量明显低于白天的液流量,柽柳的夜间液流现象是在补充白天因强烈蒸腾而导致的自身水分亏缺,而且不同土壤水分条件下的夜间树干液流速率存在差异。柽柳液流速率和液流量在7月初地下水位较低时,较为稳定的土壤含水量促进了柽柳蒸腾,树干液流速率均达到了观测期的最大值。样柳树干液流速率变化与太阳辐射、空气温度呈显著正相关关系。7月中旬,地下水位迅速上涨,土壤含水量达到最大值,受到了淹水胁迫,柽柳在该阶段内保持最低的蒸腾量,柽柳树干液流速率变化与环境因子相关性不显著。8月下旬,当土壤水量持续下降,与土壤含水量显著负相关,树干液流速率开始上升并保持在一个较高的水平。更多还原

【Abstract】 Water is one of the important factors effects the ecosystem stability in arid area, regional hydrological processes dominate ecological processes. Excess development and utilization of water resources caused by population growth and social and economic development abounds in arid areas, giving rise to the contradiction between production water and domestic water and ecological water and a series of environmental problems like ecological environment deterioration, and seriously confining sustainable development of regional economy and sustainable improvement of people’s living environment. The primary cause of the deterioration of ecological environment is irrational distribution of water resources, which results in the conflict between national economical water requirement and ecological and environmental water requirement. Hence, to solve the ecological environment deterioration problem in arid region, water resources must be rationally allocated. The key problem of water allocation is to determine ecological water requirement. As the cycle process of water in the soil-plant-air continuous system is very complex, it is hard to determine various water ins and outs accurately and precisely in water balance calculation. However, the effects of vegetation in various parts of hydrology cycle process and its response to different environmental variations make it very important to the relationship between vegetation and soil water in water budget process. What strategy would plant adjust to water stress under the ecological environment characterized by wind and sand and drought? How plants coexisting in the same place avoid excess competition for water? With the intensification of water resources development and utilization, what impacts would groundwater decline and surface runoff decrease have on plants? When the climate change result in the variation of precipitation quantity and form, different plants would have what kinds of responses? To answer these questions, it is essential to study the origins of plant water. In addition, researching how do plants make use of the limited water and responses to hydrological rhythm change have significance for maintenance of ecosystem stability.Under the background above, in our research, we choose Tamarix ramosissima Ledeb as the object, which is an excellent wind-breaking and sand-fixing shrub species widely distributed in the riparian of middle reaches of Heihe River..On the basis of Predeeessors’work and the adoption of stable isotope technique and advaneed Dynamax’s thermal banlence Probe method, we have a detailed analysis on about the water absorption, characteristics of stem sap flow, WUE, and water utilization, in order to clarify the response mechanism of T. ramosissima under different hydrology processes.The main study results are as follows:1. Hydrology processes and D and18O isotopic characteristics of riparian waterThe study area rainfall scarce and has concentrated features:rainfall commonly occur in every June-September, Heihe River water level and observation points during the underground water level fluctuation are more frequent; Because it’s the soil water content, with gas rainfall years and uneven distribution of different length for the rainy season, dry weather underground water level fluctuation gently; The rainy season by artificial storage effect, rainfall and water supply side effects, rivers and underground water original joints was changed, the response to go up drop in groundwater time lag effect, among them, at the end of June to mid August, the time lag of about three days, the late into the rainy season lag time reduced to less than one day. Two observation are nodded at different distances away from the river, because of make lateral velocity flow route by infiltration on the length of the larger impact, and at the same time, the differences of media types, and caused the soil infiltration coefficient vertical division exist, these factors, leading to the change of underground water level a response on vertical direction gradient river there.The LMWL was δD=8.01δ18O+1.51(r2=0.94, n=136), with smaller intercept. The d-excess went higher in winter and became lower in summer. The8D and δ18O values of precipitation presented an obvious seasonal variation:the isotopic composition of precipitation in rainy season in2008fell on the Local Meteoric Water Line(LMWL), its δD-δ18O relationship line was close to LMWL and a little lower than Global Meteoric Water Line(GMWL), and its intercept was approximately equal to that of LMWL. All of these showed that the water vapor originates from ocean and it belongs to monsoon rainfall. The isotopic composition of precipitation in dry season fell on the upper left of Local Meteoric Water Line(LMWL), its slope was far lower than that of LMWL and GMWL, and its intercept were larger than that of LMWL. These not only indicated that precipitation experienced evaporation and accumulation effect, but also implied that water vapor came from evaporation of local surface water and groundwater and transpiration of plant leaves. During observation, the isotopic composition of D and18O in river water presented an increase trend compare to the river water in Qilian mountain Pass. For one thing, river water, an open water system, underwent intense evaporation and caused heavy isotopes to accumulate; for another, precipitation water whose isotopic composition were more positive or water from upper reach reservoir recharged the river. In rainy season, there were positive correlation of3D and δ18O variation of between river water and precipitation, showing that rainfall was the main recharge source of river. Average values δ18O and δD in groundwater remained constantly, suggested that groundwater was recharge from Qilian mountain.Soil water content (SWC) varied under different site conditions. Rain had little impact on the deeper soil water potential but the surface soil. And the soil moisture of different soil depths in different sites varied significantly. The average values of δ18O in soil water samples increased as soil depths grew and the upper soil layer could be easily affected by environmental factors.2. Dependence of plants on groundwaterBy comparing theδ18O values of T. ramosissima stem water with those of various water resources, it was found that the Depth of water extraction by plants varied with the change of seasons. For T. ramosissima in NO.1site, When the groundwater level is low, T. ramosissima absorbs shallow soil water (15-35cm), while the groundwater level is high, it absorbs deep soil water (deeper than60cm), the root system of T. ramosissima is quite Plastic,which can help the Plant to adapt to different water capacity in different ground substanees. For For T. ramosissima in NO.2site, Throughout the growing season,the water utilization source for T. ramosissima was from shallow soil water (15-35cm). T. ramosissima in both sites did not take up rain water or river water during study period. T. ramosissima absorb soil water in a definite range of depth and its absorption depth was affected by groundwater level.3. WUE of T. ramosissima in riparianThe13C value of leaves was measured to evaluate the intrinsic water-use efficiency (WUE) of plant. The13C measurements indicated that all plants have higher in the is13C value (high WUE) in arid month (July) under low groundwater level, and lower13C value (low WUE), in wet months when groundwater rosing.4. Transpiration water consumption of T. ramosissima in riparianThe daily variation of sap flow velocity of T. ramosissima is wide-peak curve, and there is a phenomenon of "nap". It can be divided into four stages:rapid ascending period, stationary period, rapid descending period and nighttime period. The variation is mainly influenced by factors such as solar radiation, air temperature, relative air humidity, soil moisture and wind speed. There is nighttime water compensation in T. ramosissima. Nighttime sap flow still exits, but compared to daytime sap flow, the rate variation at night is slow, the curve is relatively smooth and the amount of sap flow is obviously lower. This is to compensate for the water deficit caused by strong transpiration during the day, and the nighttime sap flow rate in different soil water conditions are different. There is a difference sap flow velocity in T. ramosissima. In early July, the sap flow velocity are the highest in the grow season, when present a high soil water content, the sap flow velocity variation has positive correlation with solar radiation and air temperature. while that in middle August reach the lowest in the grow season with the sap flow velocity, the sap flow velocity variation has no significant correlation with environmental factors..In August and September, the sap flow velocity and sap flow capacity begin to increase with the drop of soil moisture, he sap flow velocity variation has negative correlation with soil moisture.更多还原