Knowledge Resource Center for Ecological Environment in Arid Area
| 沙坡头地区主要固沙灌木的水分利用特征研究 | |
| 其他题名 | The Water Use Characteristics of sand-fixing shrubs in Shapotou Area |
| 鲍婧婷 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 李新荣 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 植被重建能有效遏制沙漠化的发展, 减轻风沙危害和促进局地生境恢复。然而随固沙年限的增加，在许多地区出现了原来高密度、种类相对单一，以乔木为优势的人工植被大面积的衰退，而种植密度和盖度相对较小、种类组成多样、以旱生灌木为主的植被则具有很好稳定性的现象。了解固沙植物的水分利用特征是解释以上实践中存在问题的重要前提之一。现阶段，针对固沙灌木的生理生态学研究热点主要集中在植物抗旱性能的评价、鉴定以及对干旱胁迫的响应等方面，而对其耗水规律及水分利用特征的研究报道相对较少。植物水分利用特征是植被重建工程中的植物种选择、植被密度控制与空间优化配置、以及固沙植被能否可持续性的核心问题之一。本文从植物生长、水分关系、光合生理的角度，在植株的叶片水平上研究固沙灌木的水分利用特征，通过比较不同林龄、不同林分密度以及不同固沙灌木的光合和水分生理生态特征差异，分析产生这些差异的生理机制，从而揭示林龄、林分密度等对固沙灌木的水分状况以及光合、水分利用特征的影响，旨在为固沙植物群落的碳水平衡研究提供生理生态学基础，为固沙灌木林的合理配置提供科学依据。本研究主要结果如下： 1. 比较低密度（2 m × 2.5 m）、中密度（1.5 m × 2 m）和高密度（1 m × 2 m）三个常见的密度固沙植被中的沙木蓼（Atraphaxis bracteata A. Los.）单株生长、光合和水分特征，我们发现，三者在地上生物量以及生长速率方面差异显著(p<0.05)，表现为高密度沙木蓼植株个体矮小，叶片稀疏，而中密度和低密度没有明显的差异。在生长季降水较多的时期，三个密度沙木蓼的光合及水分生理差异并不显著(p>0.05)，而在干旱胁迫严重时，高密度沙木蓼的新枝水势（Ψ）、叶相对含水量（RWC）、最大净光合速率（Amax）、蒸腾速率（E）、气孔导度（Gs）和水分利用效率（WUE）都低于中、低密度，且叶绿素荧光参数Fv/Fm值也显著降低(p<0.05)，说明高密度沙木蓼的光合性能、水分状况、水分利用效率等较低。在2014年生长季初期发生的严重干旱，导致高密度沙木蓼大部分植株濒临死亡。以上结果初步显示，将固沙灌木沙木蓼的初植密度定为1 m × 2 m不利于植被的稳定，而2 m × 2.5 m和2 m × 1.5 m的差异不显著(p>0.05)，可能是植物生长年限较短，密度效应还未显现。 2. 固沙植被中原来种植的灌木种，随固沙年限的增加而容易发生退化(盖度、密度和生物量减少)，除了灌木种群扩大增加了土壤水分的利用，以致超出土壤水分的植物承载力而发生退化外，那么灌木本身的生物学特性，如年龄结构起着什么样的作用？为探明灌木年龄与其退化的关系，野外原位测定了不同林龄柠条（Caragana korshinskii Kom.）（3 a，13 a，25 a）的新枝水势、叶相对含水量、，净光合速率和水分利用效率，分析了其光合特性与植物水势的关系，结果表明：1）不同林龄柠条的光合能力和水分利用效率差异显著(p<0.05)，表现为中龄、幼龄的光合能力高于老龄，而水分利用效率低于老龄；2）净光合速率、气孔导度与新枝水势的非线性关系，反映出不同林龄柠条采取不同策略应对干旱胁迫，幼龄柠条通过快速关闭气孔来减少水分散失，而中龄和老龄柠条通过调整水分利用策略来应对干旱。老龄柠条通过提高水分利用效率来使水分利用最大化，但其植物水势和光合的降低可能导致生长减缓和衰退。 3. 柠条、沙木蓼和油蒿（Artemisia ordosica Krasch.）作为沙坡头地区的主要固沙植物，都具有抗旱、抗风蚀、耐高温和沙埋的特点，发挥了良好的防风固沙效益。但是这三种固沙灌木在形态结构、抗旱性特征以及水分利用特征等方面差异较大，形成了各自独特的生态适应策略。三者的生长态势明显不同，无论从生物量积累还是生长速率来看，都显示沙木蓼生长最快且地上生物量最高，油蒿次之，而柠条生长相对较慢，但在水分充足时柠条能快速生长，有较强生长潜力。柠条的水分状况较差，其受干旱胁迫的程度较严重，进而导致其光合速率的降低。油蒿表现为高光合、高蒸腾和高气孔导度，柠条则是低光合、低蒸腾和低气孔导度，而沙木蓼介于两者之间。三种灌木水分利用效率在干旱严重时表现为柠条WUE最高，而在水分较好时油蒿WUE较高，沙木蓼介于两者之间。表明油蒿采取了消耗型的水分利用策略，而柠条采取了节约型的水分利用对策。沙木蓼的光合能力和蒸腾耗水接近油蒿，但其WUE在水分亏缺严重时低于柠条，在水分比较充足时又低于油蒿，其Fv/Fm值和RWC值在生长季末均显著低于柠条和油蒿(p<0.05)，表明其生理过程受生长节律影响的程度较强，同时表明沙木蓼对环境变化的适应性较差，以上表现都可能使其在与柠条、油蒿竞争中处于劣势地位。 根据以上结果，我们认为：合理地控制固沙植物的密度，是确保沙地植被-土壤系统水量平衡的，实现固沙植被可持续性的重要举措；分析固沙植被退化原因时，除了考虑植被-土壤系统水量平衡，特别是土壤含水量的相对稳定外，还要考虑植被，特别是主要固沙植物的生物学特性，例如植物的年龄和水分利用关系对植被稳定性的影响，因此，衡量主要固沙植被能否自我更新也是未来进行固沙植被建设应考虑的一个关键问题。 |
| 英文摘要 | Artificial revegetation can effectively prevent the development of desertification, reduce sand burial hazards and promote local habitat restoration. The long-term positioning study of revegetation in arid desert region of China showed that the planted xerophytic shrubs have achieved the anticipated target in revegetation and restoration practice according to the pattern of dominance vegetation with different life forms. However, with the sand-fixation time, large areas of the recession in the dominant artificial tree vegetation happened in places with high densities and single species, but the artificially revegetated areas with relatively low planting density, low coverage and more diverse species composition, have been kept in good stability. Up to date, many researches of physiological ecology of sand-fixing shrubs are focused on the evaluation of plant drought resistance, identification and response to drought stress, etc., while little is known about the plant water consumption and characteristics of water use. Plant water use characteristics thus play a key important role in choosing revegetation species, optimizing the revegetation density and the plant species collocation ratio, determining water consumption thresholds in arid desert area and predicting soil water balance and succession orientation issues.We planed to study the characteristics of water use of sand-fixing shrubs as far as the plant growth, water relations and photosynthesis physiological were concerned. Then, we compared the photosynthetic and water physiological differences in classes of ages, planting densities and different types of sand-fixing plants shrubs, and analyzed the physiological mechanisms inherent. This work would shed light on physiological ecology for the carbon balance of sand-fixing plants on water usage basis, and provide a scientific basis for the rational allocation of sand-fixing shrubbery. The main results and conclusions are as follows: The plants with different planting densities showed significant growth rate and above-ground biomass. The plants with high planting density (1 m × 2 m) were significantly lower and had less number of leaves than those with low planting density (2 m × 2.5 m) and medium planting density (1.5 m × 2 m) while no significant differences were found in low density and medium density. In more precipitation period during the growing season, no significant differences were found in new shoot water potential (Ψ), leaf relative water content (RWC), the maximum net photosynthetic rate (Amax), transpiration rate (E), stomatal conductance (Gs) and water use efficiency (WUE) between low density, medium density and high density of Atraphaxis bracteata. However, the gas exchange parameters and RWC undergone significant changes under moderate drought stress while the chlorophyll fluorescence parameters changed significantly only under the severe drought stress. Amax, Gs and RWC tended to decrease, while the leaf temperature tended to increase and no obvious change in E. Drought stress showed no significant effect on the gas exchange parameters except for the decrease in Amax, but had a significant impact on light response curves and shortened the effective photosynthetic time. Under severe drought stress, the photosystem was damaged and showed a weakened metabolism. The Fv/Fm and ΦPSII values decreased significantly, while NPQ increased significantly. The impact of stomatal limitation and non-stomatal limitation on net photosynthetic rate were related to the intensity of drought stress. Under moderate stress, stomatal limitation play a leading role, while the non-stomatal limitation under severe stress. Almost all plants with high density were near to death under the severe drought stress in the early stage of growing season in 2014, indicating the poor drought tolerance of Atraphaxis bracteata. All the results mentioned above showed that the density with 1 m × 2 m was disadvantage to the growth of Atraphaxis bracteata, while little difference were showed between the densities of 2 m × 2.5 m and 2 m × 1.5 m, which may be attributed to the short planting time and the density effect isn’t showed. Caragana korshinskii is widely used for sand-binding in the Shapotou area. They have adapted well to the habitat during the establishment. With the increasing age and the consumption of available soil water, the initially-planted C. korshinskii had degraded. To examine the relationship between the shrub age and the population degradation, we conducted field experiments on different-aged C. korshinskii (25-year-old, 13-year-old and 3-year-old) for the measurements of leaf water potential, leaf relative water content, leaf-specific apparent hydraulic conductance, photosynthetic rate and water use efficiency. We analyzed the relationships between photosynthetic properties and leaf water potential among the different-aged shrubs. The results showed that the photosynthetic capacities of young-mature and juvenile were higher than those of old-growth, while their water use efficiencies were lower compared to old-growth. The nonlinear relationships between both Amax and Gs with leaf Ψ show that different-aged C. korshinskii plants adopt different drought response strategies. Juveniles reduce water loss through closing stomata, while older C. korshinskii plants respond to drought by adjusting WUE. Although the old-growth C. korshinskii maximized water use by increasing the WUE, the decreased photosynthesis and plant water potentials would slow the growth of plants and lead to their degradation.As pioneer species in revegetated area in Shapotou, Caragana korshinskii, Atraphaxis bracteata and Artemisia ordosica have the characteristics of drought resistance, wind erosion, high temperature and sand burial tolerance, and play an important role in windbreak and sand-fixation. But these three sand-fixing shrubs are quite different in morphology, drought resistance characteristics and water use, etc., which form their own unique ecological adaptation strategies. They showed the distinct growth trend, in terms of biomass accumulation or growth rate, Atraphaxis bracteata showed the fastest growth rate, followed by Artemisia ordosica and Caragana korshinskii. While Caragana korshinskii showed the strongest growth potential with adequate moisture. The water status of Caragana korshinskii was poor and was stressed by drought, leading to lower photosynthetic rates. Artemisia ordosica exhibited high photosynthesis, high transpiration rate and high stomatal conductance, while Caragana korshinskii exhibited low photosynthesis, transpiration rate and low stomatal conductance. The values of Atraphaxis bracteata were between Artemisia ordosica and Caragana korshinskii. Among the three shrubs, Caragana korshinskii showed the highest WUE under severe drought stress while Artemisia ordosica in adequate moisture condition. The values of Atraphaxis bracteata were still between Artemisia ordosica and Caragana korshinskii，indicating that Artemisia ordosica adopted the water consumption strategy while Caragana korshinskii had a water-saving mechanism. The photosynthetic capacity and water consumption by transpiration of Atraphaxis bracteata were near to Artemisia ordosica, but its WUE was lower than that of Caragana korshinskii under severe drought stress and lower than that of Artemisia ordosica with adequate moisture. The Fv/Fm and RWC values of Atraphaxis bracteata were significantly lower than those of Caragana korshinskii and Artemisia ordosica at the end of the growing season, indicating that the physiological process was mainly controlled by its growth rhythm and indicating the poor adaptability of Atraphaxis bracteata to environmental change. Collectively, all of these traits mentioned above indicate that Atraphaxis bracteata is disadvantaged in the competition with Caragana korshinskii and Artemisia ordosica in desert ecosystem.Based on these results, we conclude that the reasonable control of the density of sand-fixing plants will help ensure the sand vegetation-soil system water balance and achieve sustainability. In addition to the vegetation-soil system water balance and the relative stability of soil moisture, we should also consider the biological characteristics of the sand-fixing plants, such as the plant age and the water relations on the stability of the plants. Therefore, the ability of plant self-renewal is a key issue for constructing revegetation in the future. |
| 中文关键词 | 柠条 ; 沙木蓼 ; 油蒿 ; 固沙灌木 ; 水分利用策略 |
| 英文关键词 | Caragana korshinskii Atraphaxis bracteata Artemisia ordosica photosynthesis water-use strategy |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287719 |
| 推荐引用方式 GB/T 7714 | 鲍婧婷. 沙坡头地区主要固沙灌木的水分利用特征研究[D]. 中国科学院大学,2016. |
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