ISWC OpenIR  > 水保所知识产出(1956---)
杠柳适应黄土丘陵干旱环境的生理生态策略
安玉艳
Subtype博士
2011-05
Degree Grantor中国科学院研究生院
Place of Conferral北京
Keyword种子萌发策略 干湿交替 极端干旱 整体抗旱性 形态解剖结构
Abstract

干旱胁迫是全球范围内影响植物生存、生长和分布的最重要环境因子。黄土丘陵区是典型的干旱半干旱地区,由于生态环境的脆弱性和长期人类活动的干扰以及过度利用,导致水土流失加剧,植被覆盖率低。严重阻碍了区域社会经济的快速协调发展与黄河下游的安全。开展黄土丘陵区生态恢复研究是解决这些问题的关键。水分亏缺是制约黄土丘陵植被恢复与重建的关键因子,在全球暖干化的背景下,干旱胁迫可能会更加严重,并使该区的生态环境更加恶化。因此,深入研究黄土丘陵区乡土植物对干旱环境的响应机制和生理生态适应策略,具有非常重要的理论和实践意义。
本文以黄土丘陵区广泛分布的乡土灌木杠柳(Periploca sepium Bunge)为研究对象,采用野外生态学试验和人工控制试验相结合的方法,系统地研究了杠柳的对不同水分条件或不同干旱处理方式的响应,探讨了杠柳的抗旱能力,揭示了杠柳适应干旱环境的繁殖策略、种子萌发策略、形态解剖策略、各器官相互协调的整体抗旱性策略和极端干旱条件下的生存策略。主要研究结论如下:
(1)在土壤水分成为植物生长的主要限制因素的黄土丘陵区,阳坡杠柳的营养生长和生殖生长却显著优于阴坡生长的杠柳,杠柳为阳性喜光植物;阳坡单株杠柳平均产19对蓇葖果,为阴坡的9倍;且阳坡杠柳所产蓇葖果明显大于阴坡,前者单个蓇葖果含种子66±7.25粒,后者含种子45±8.09粒;阳坡杠柳单株种子产量最高可达9900粒,平均约为2376粒。而阴坡单株杠柳种子平均产量仅为180粒。
(2)杠柳种子萌发对光不敏感;从4 ℃到40 ℃的恒温条件下以及从10/4 ℃到 40/35 ℃的变温条件下杠柳种子均能很好萌发;杠柳种子萌发喜温,在30 - 40 ℃下的萌发速度显著高于低温条件下的萌发速度;变温可加速杠柳的种子萌发;杠柳种子萌发可忍耐中度PEG 渗透胁迫(-0.6 MPa),在渗透胁迫中未萌发的种子仍然保持着生活力且在胁迫解除后萌发更快;短期吸水再回干不影响杠柳种子生活力,而且回干后的种子再次吸水时的萌发速度明显加快;当吸水种子回干时,萌发进程中止,但回干种子保持着萌发过程中的生理进展;渗透胁迫的主要影响是延长了杠柳种子萌发的第二阶段;杠柳种子在水分亏缺下萌发率的降低或萌发的停止,以及只在适宜水分下的快速大量萌发是杠柳适应黄土丘陵干旱环境的两个特殊的生存策略,能够保障种子在足够多的水分下大量快速萌发。
(3)夏季持续干旱6 d后杠柳光合速率降低的主要原因是气孔关闭,光合机构并未受到不可逆的伤害;复水后杠柳光合速率显著高于对照,表现出明显的补偿效应。杠柳各器官O2·-产生速率和MDA含量均表现为老叶>成熟叶片>幼叶>新茎>细根;杠柳各器官的O2·-产生速率均表现为在干旱条件下升高,但幼叶、新茎和细根的MDA含量在干旱下反而是降低的;SOD、CAT和POD 3种保护酶对不同器官抗氧化能力的贡献不同,其中细根中3种保护酶活性对土壤水分敏感,均为水分亏缺则活性升高,复水则活性降低。杠柳的溶质积累具有器官特异性特征,同时表现在所参与的溶质的种类和各溶质的变化幅度上。在反复干旱条件下,源器官(成熟叶片和老叶)相对稳定,而溶质积累对库(幼叶、新茎和细根)器官更加重要。优先保护和保留幼嫩的生命力旺盛的组织、较强的旱后修复和补偿能力、茎和根的储藏性作用以及各器官间的相互协调配合是杠柳适应干湿交替低水多变环境的重要机制和策略。
(4)陕北黄土丘陵区杠柳的叶片为狭长形,而地处暖温带半湿润气候区的杨凌杠柳的叶片呈阔卵圆形;前者叶面积极显著小于后者,但前者的叶片数和分枝数显著大于后者;与杨凌杠柳相比,黄土丘陵杠柳叶比重大,叶片组织结构疏松度小,上、下表皮角质层加厚,上表皮角质层尤其发达,叶表面气孔小但密度大,且这些差异均达显著性水平。与陕北杠柳相比,杨凌杠柳的总结实量、单株蓇葖果对数、蓇葖果长和直径、以及果生物量占总生物量百分比等结实特征指标均显著减小,且其对水分亏缺敏感,在中度干旱下的结实量很少,严重干旱下无种子产生。
(5)当停止浇水使土壤水分降至设定水平的过程中,杠柳的生长速率和耗水量急骤降低,但当恒定胁迫持续一段时间后,3种恒定土壤水分条件下的杠柳叶片的黎明前叶水势、相对含水量、MDA含量和3种保护酶活性随胁迫时间延长均无显著性变化。杠柳在35%FC条件下的MDA含量一直显著低于80%FC。说明杠柳在恒定干旱胁迫下能够主动调整生长生理状态适应新的水分条件,并最终变胁迫为“非胁迫”。
(6)当土壤水分含量降至7.07%(干旱15 d),4.65%(干旱27 d),3.09%(干旱42 d)时杠柳的成活率分别为100%、90%和30%,且复水后新生枝条的生长速率远大于适宜水分处理。持续干旱处理杠柳的MDA含量在干旱18 d(土壤含水量为6.35%)时急剧升高,此时,除个别从根部萌发的幼嫩枝条外所有叶片均死亡,一触即可脱落。极端干旱下,杠柳叶片加速衰老死亡、以休眠芽形式进入相对休眠状态,降低代谢,缓慢利用有限的水分和养分资源。复水后根系和茎复苏长出新芽并补偿生长,这是杠柳在极端干旱下的落叶相对休眠-复水后复苏型生存策略。
(7)杠柳根皮又称香加皮,为《中华人民共和国药典》收录药材。水分条件匮乏的阳坡杠柳根皮中4-甲氧基水杨醛含量显著高于水分条件相对优越的阴坡杠柳。黄土丘陵区杠柳根皮4-甲氧基水杨醛在整个生育期的含量均大于0.35%,达到并超出《中华人民共和国药典》规定水平0.2%,这表明杠柳可作为一种药用植物在陕北黄土丘陵区大面积种植,且适合种植在水分条件最差的阳坡。此外,杠柳的叶、根皮和茎皮的多种杀虫活性成分具有重要的生态防御性作用。
综上所述,杠柳是一种集避旱和耐旱机制于一体而适应于干旱生境的典型旱生药用植物,且具有适应黄土丘陵干旱环境的特殊种子萌发策略以确保种群的自我更新。将杠柳作为一种耐旱药用植物在黄土丘陵区水分条件最差的阳坡大面积种植可确保存活率、保存率和生长率,同时兼顾生态与经济效益。
关键词:种子萌发策略,干湿交替,极端干旱,整体抗旱性,形态解剖结构

Other Abstract

Drought is the most important factor limiting plant establishment, growth and distribution in many regions of the world. The Loess hilly region is a typical semi-arid and arid region in northwest China. The harsh environments and long-term anthropogenic disturbance had resulted in severe soil erosion and water loss, vegetation degradation and fragile ecosystems. These conditions seriously impede the fast and coordinated social, economic development and the safety of the lower Yellow river. Therefore, it is the key to solve these problems that carrying out ecological restoration and reconstruction in the Loess hilly region. Water deficit is an important limiting factor for the ecological restoration in this region. Moreover, due to the global climate change, an increased frequency and severity of drought stress might occur at a regional scale in the Loess hilly region, which will worsen the ecological environment. The selection of appropriate plant species for vegetation restoration is an important issue at present and in the future. The research on responses of native species to water deficit conditions and their eco-physiological adaptation strategies to drought environment in the Loess hilly regions could provide insights into the improvement of the vegetation restoration, and therefore, are of great theoretical and practical significance.
In this paper, Periploca sepium Bunge which is a native species and widespread in the Loess hilly region was chosen as experimental material to study the eco-physiological adaptation strategies of native species to local drought environment. Using the method of field investigation and manual control experiments, we systematically investigated the responses of Periploca sepium plants to different water conditions or drought patterns. The  drought-resistance of Periploca sepium was analyzed and discussed. The adaptive strategies including reproductive strategy, seed germination strategy, morphology and anatomy strategy, the whole-plant strategy by coordination of all organs and the survival strategy under extreme drought condition were revealed. The main results were as follows:
(1) As a heliophilous plant, the vegetative growth and reproductive growth of Periploca sepium plants in sunny slope were significantly better than that in shady slope, although the soil moisture is a major limiting factor of plant growth in the Loess hilly region. The average seed production of single Periploca sepium plant in sunny slope was 19 pairs of follicles, which was 8 times higher than that in shady slope. Moreover, the follicles produced by Periploca sepium plant in sunny slope were significantly larger than that in shady slope. The single former follicle contained about 66±7.25 seeds, while the later one contained 45±8.09 seeds. The single sunny slope plant could produce seeds as many as 9900, and the average production (seed number) was 2376, while the shady slope plants produced only 180 seeds on average.
(2) Seed germination of Periploca sepium was not influenced by light. Seeds germinated at a wide range of temperatures (constant temperature: from 4 to 40 ; ℃alternating temperature with 5 difference: from 10/4 to 40/35 ; alternating ℃℃temperature with 10 difference: from 15/4 to 40/30 ). Seed germination of ℃℃Periploca sepium was thermophilic, and the germination rate at 30-40 was much higher than that ℃at lower temperatures. The alternating temperature regimes accelerated the germination rate. Seed germination of Periploca sepium could tolerate moderate PEG osmotic stress (-0.6 MPa). The ungerminated seeds in osmotic stressed condition remained viable and germinated more rapidly when the stress was relieved. Hydration-dehydration pretreatment did not affect seed viability, and the pre-treated seeds germinated much faster when re-watered. The germination process ceased when hydrated seeds re-dried, however, the physiological advancement during hydration was maintained. Osmotic stress prolonged the second phase of seed germination to make sure slow but sufficient hydration and to accumulate enough energy. The low or none germination under water deficit conditions and the larger and more rapid germination when seeds are provided with enough water is two strategies for seedling establishment of Periploca sepium in drought-prone regions. Rapid germination occurs only after a major rainfall event or prolonged rainy weather. In  this case the emerged seedling has access to sufficient water to enhance its chances to survive and to complete its life cycle.
(3) Stomata closure was the main factor limiting Periploca sepium photosynthesis when plants were with-held water for 6 d during summer, and the photosynthetic apparatus did not show any irreversible damage. The photosynthesis rate of re-watered plants was significantly higher than that of control plants, showing a significant compensation effect. The production rates of superoxide anion radical (O2·-) and malondialdehyde (MDA) contents in all organs were expressed as: old leaves> mature leaves> young leaves > new stems> fine roots. The MDA contents in young leaves, new stems and fine roots declined, although their production rates of O2·- increased under drought conditions. SOD、CAT and POD contributed differently to the antioxidant capacity. These three enzyme activities in fine roots were all sensitive to soil moisture, increasing under water deficit conditions and declining when re-watered. The solute accumulation of Periploca sepium plants showed an organ-specific characteristic, which were reflected both in magnitude and in the type of solutes involved. The source organs (mature and old leaves) were stable under repeated stress conditions, and the accumulation of compatible solutes was important mainly for sink organs (young leaves, new stems and fine roots) with increasing drought cycles. The preferential protection of young tissues from the oxidative stress induced by water deficit conditions, the strong repair and compensation capacity during rehydration, the storage role of stem and root, and the cooperation of all organs are the important adaptive mechanisms and strategies of Periploca sepium to the drying and wetting conditions in drought-prone regions.
(4) The leaves of Periploca sepium plants in the Loess hilly regions were elongated, while plants in Yangling where is of warm sub-humid monsoon climate had ovaideleaves. Moreover, the former leaf area was significantly smaller than the later, but the leaf number was exactly reversed. Compared with plants in Yangling region, the Periploca sepium plants in the Loess hilly region showed greater leaf specific gravity, smaller leaf tissue structure loose ratio, thicker upper and lower cutin layers, smaller but more stomata, and these differences were statistically significant. Compared with plants in the Loess hilly region, the Periploca sepium plants in Yangling region showed significantly smaller seed production, number of follicles per plant, average length and diameter of follicles and the  ratio of fruit biomass to total biomass, and these index of Yangling plants were more sensitive to soil moisture, for example, its seed production was low under moderate drought condition and no seeds were produced under severe drought condition.
(5) The growth rate and water consumption of Periploca sepium plants decreased abruptly when water was with-held. However, after a period of constant stress, the predawn leaf water potential, relative water content, MDA content and activities of 3 antioxidant enzymes showed none significant changes with the stress time under all 3 constant drought conditions. The MDA content in plants under 35%FC soil water condition was significantly lower than that under 80%FC soil water condition all the time. These results indicate that Periploca sepium is able to adjust its growth and physiological state to the new soil water condition under constant drought stress, and its adaptive strategy is achieving new stable state and turning the stress to “non-stress”.
(6) The survival rates of Periploca sepium were 100%, 90% and 30% when soil water content dropped to 7.07% (water with-held for 15 d), 4.65% (water with-held for 27 d) and 3.09% (water with-held for 42 d), respectively. The leaf MDA content in plant increased sharply when naturally drought for 18 d (with soil moisture content of 6.35%), and until then, all leaves were senescent and dead, except leaves of individual young shoots sprouting directly from roots. Under extreme drought conditions, Periploca sepium accelerated its leaf senescence in order to slow down the metabolism and the use of limited water and nutrient resources. At the same time, lots of dormant buds generated and the whole plant became relatively dormant. In this way, Periploca sepium could live through the extreme drought condition. The dormant buds sprouted rapidly when plants were re-watered and showed obvious compensatory growth. These results suggest the survival strategy of Periploca sepium by defoliating leaves and entering relative dormant state under drought and recovering quickly when re-watered.
(7) The root bark of Periploca sepium, also known as cortex periolocae, is a traditional Chinese medicinal material. In our experiment, the content of 4-metho- xysalicylaldehyde in root bark of Periploca sepium plants in sunny slope were significantly higher than that in shady slope where the soil moisture condition is much better. The 4-methoxysalicylaldehyde content in Periploca sepium plants growing in the Loess hilly region were higher than 0.35% during the whole growth period, while the standard content  

Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8894
Collection水保所知识产出(1956---)
Recommended Citation
GB/T 7714
安玉艳. 杠柳适应黄土丘陵干旱环境的生理生态策略[D]. 北京. 中国科学院研究生院,2011.
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