【作者】 朱桂才；

【导师】 杨中艺；

【作者基本信息】 中山大学 ， 生态学， 2011， 博士

【摘要】 水分过多或过少对植物生长都不利。近年来,由于水分环境条件的剧烈变化,涝害和旱害的现象时有发生。因此,水分逆境下植物的适应程度及其耐性机理研究日益受到重视。李氏禾能忍耐长时期的干旱、淹水,被报道成功应用于江河湖泊的消涨带植被恢复,关于其忍耐水分逆境的机理尚未见系统报道。本研究采用模拟淹水和干旱处理,从常规及逆境下的基本生物学特性研究着手,明确了李氏禾忍耐干旱、淹水的强度;研究了李氏禾营养器官的解剖结构和根系生长参数、叶绿素含量及叶绿素荧光特性、过氧化酶系活性与内源激素含量等对水分胁迫的响应,初步建立了水分逆境的生理生态适应机制;探讨并确立了李氏禾高效繁殖的技术,为李氏禾在受损人工生态系统植被恢复实践中推广应用提供理论和技术支撑。研究结果如下:1.采用地上部休眠率评价多年生草本植物忍耐逆境的能力,经持续淹水(淹没)120d,地上部休眠率仅10%;间断性干旱和持续干旱(土壤水分含量低至2.74%)45d,其地上部保持活力的植株分别为50.0%和30.0%。结果表明,李氏禾具有较强的抵御水淹和干旱的能力。2.李氏禾根、茎、叶的解剖结构受淹没胁迫影响的程度大于淹涝胁迫。淹涝时,李氏禾的茎、叶结构变化幅度很小,只在淹涝后期根内组织细胞部分解体,形成空腔。淹没后李氏禾叶片维管束鞘结构减少,但不失绿;随淹没时间延长,靠近茎中心的薄壁细胞减少,形成特定的通气组织;根内部组织解体形成空腔;淹没60d后,李氏禾的营养器官还能保持总体结构的完整性。干旱胁迫下,气孔开度减小,茎表皮角质化,根皮层增厚,但导管和韧皮纤维等机械输导组织较常见的水生植物发达。根系参数分析表明,李氏禾以增加根长、根表面积、根直径、根体积适应淹涝状态,以显著增加根的直径适应淹没逆境,且淹水胁迫解除后根系生长参数能恢复到胁迫前的水平。深入了解营养结构、根系参数对水分胁迫的响应,有助于更深入理解李氏禾与环境的关系,特别是在逆境下的适应变化。3.自然条件下,李氏禾4月蒸腾速率较高,6月和10月日均叶周围空气相对湿度(RH)较大,光利用效率(LUE)10月>4月>6月。淹水处理后,李氏禾叶片Chla的含量均高于Chlb的含量,淹涝后叶绿素总含量高于对照,呈震荡上升;正常条件下,李氏禾Chla/Chlb比值约为3:1,淹没降低了叶绿素含量,且对Chla破坏大于Chlb,淹没胁迫使李氏禾Chla/Chlb比值急剧下降,且一直保持较低水平;随淹涝时间延长,Chla/Chlb基本不变。4.淹水和干旱引起李氏禾光合特性发生变化。淹涝状态下,李氏禾的PSⅡ实际光能转化效率(Yield)、光化学淬灭系数(qP)随淹涝时间延长变化幅度不大,光合作用受淹涝影响小,光合系统的稳定主要靠热耗散(qN)维持。淹没后,Yield和qP明显下降,热耗散(qN)值低。淹没状态下李氏禾仍能保持光合作用,且淹没出露后Yield和qP能恢复到淹没前水平。干旱胁迫下,Yield和qP先上升,但随胁迫加剧后下降,降幅不大。qN随干旱程度加剧总体表现为上升趋势,李氏禾启动热耗散减轻干旱胁迫下过量光能对光合机构的损伤。5.淹水和干旱引起植物有机体生理变化可以在超氧化物歧化酶SOD、过氧化物酶等指标反映,通常抗性强的植物上述指标变化幅度较小。随干旱、淹没时间延长,超氧化物歧化酶SOD活性增加,只高于对照20%;淹涝条件下,超氧化物歧化酶SOD活性小于对照;水分胁迫导致POD活性增加,叶POD活性>茎POD活性>根POD活性;根POD含量随干旱胁迫加剧而上升,但各淹水处理与对照水平持平;水分胁迫还导致过氧化氢酶CAT活性增加,增幅最高达对照的5倍;干旱胁迫下,李氏禾脯氨酸(Pro)含量增加,根、茎、叶各部位游离脯氨酸含量存在差异;在干旱30d达到最高,随胁迫加剧(干旱40d),游离脯氨酸(Pro)含量增幅减少,但显著高于对照,干湿交替与对照差异不显著。干旱胁迫对李氏禾根、茎、叶器官均有影响,淹水胁迫主要影响茎、叶,对根影响较小。李氏禾清除自由基的系统(酶促系统和非酶促系统)活性高,特别是在淹水环境下变化幅度小,膜脂过氧化程度低,能有效抵抗水分过多的伤害,即其具有一整套的抵抗系统。6.植物在感受内外环境变化、调节生长和分化发育、保持适当生存状态以适应和抵御不良环境胁迫的复杂过程中,植物激素起着关键作用。淹水后,李氏禾体内乙烯含量表现为先上升后下降的趋势,乙烯释放量在淹涝状态高于淹没状态。淹没和淹涝后,李氏禾的IAA、GA含量在胁迫初期明显上升,ABA含量也是随胁迫时间延长先上升后下降,高于对照,但变化幅度不大。淹水胁迫解除后,李氏禾IAA、ABA的含量比淹没时的明显下降,但仍高于正常生长的水平,GA含量也较对照变化明显,显示植物生理调节系统参与了对水分逆境的适应过程。激素作用的实现主要是通过浓度的改变。7.植物在其生活史过程中,以其特有的繁殖属性去适应环境,提高植物的适合度。李氏禾种子的萌发特性和无性系种群分蘖动态研究结果表明:未经预处理的李氏禾种子具有一定的种子生活力,最高达到69.5%,但发芽率较低,平均只有3.8%;常规水分管理下,李氏禾地下茎的萌芽能力强,萌芽率平均可达82.5%,且不同建植年份的李氏禾种群之间一年内分蘖数和分蘖株高有显著差异。李氏禾种子存在一定程度的生理休眠,可以利用地下茎萌芽作为李氏禾无性繁殖的有效手段。物种本身的特性和外部环境因素决定了植物对逆境的适应程度。在淹水、干旱胁迫下,李氏禾的光合系统、酶系统和生理调节系统能产生适应性变化;随胁迫解除,李氏禾有关生理活动与代谢又能恢复到胁迫前水平。李氏禾高的分蘖能力是其适应水分逆境的重要繁殖策略。总的来看,李氏禾具有较强的干旱、淹水能力,是较为理想的河岸带的水土保持植物。今后应加强外源激素诱导等途径研究激素生物合成的途径以及运输、相互作用等,深入分析不同内源激素对植物适应逆境的作用,并在耐水淹、耐干旱等特异性基因等分子生物学机理方面开展研究,建立更全面的关于植物“共耐性”水分逆境适应机理,促进李氏禾在受损人工生态系统植被恢复中的应用。更多还原

【Abstract】 Overabundant moisture or insufficient moisture are deleterious to the terrestrial plants. Recently a series of waterlogged injury and drought injury resulted from the acute variation of the moisture environment. At present, more and more studies are focused on the plant adaptability to water stress and the adaptation mechanism of stress. Leersia hexandra could adapt to the drought-flood conditions,and L. hexandra was an amphibious plants,living in the water-fluctuation belt such as rivers or lakes. However, the little information was available about its adaptation mechanism.Under the conditions of potted plants and water stress,including drought, drought-water, submerged and waterlogged, the study dealt with L.hexandra morphological, anatomical structural and physiological strategies to fit drought-flood environment. Through field investigation and control experiment, we studied the rudimental biological characteristics of L. hexandra which grow in normal and water stress environment. The results showed that L. hexandra held greater ability in the tolerance to drought-flood conditions. The dynamic response change to water stress were studied, which included the anatomical structure of nourish organ, the roots parameter, the peroxidase activity and the endogenous hormones concentration. Moreover, the mechanism of physiological ecological adaptation to adversity of L. hexandra was founded. Furthermore we researched a higher reproductive efficiency technique of L. hexandra and it was proved to have many advantages in the natural vegetation restoration schemes of disturbed habitats such as the water-fluctuation belt. The results are as follows:(1) According to the dormancy rate on ground, the plant adaptability to water stress was estimated. The dormancy rate was 10.0% after being durative waterlogged (120d). Throughout a 45_day persistent drought or drought-water period (lowest content of soil moisture was 2.74%), the survival rates remained 30.0% and 50.0% respectively. The results indicated that the ability of L. hexandra in the tolerance to drought-flood conditions was greater.(2)The anatomy structure responses extent of roots,stems and leaves under waterlogged condition was bigger than that under submerged condition. The variation extent of stems and leaves were less when L. hexandra in submerged stress. Only in the final stage of submerged stress, a vacuum formed in the root with some organ disassembling. Under waterlogged condition the vascular bundle amount reduced, but was green. With the time of waterlogged stress prolonging, the amount of folium cell in stem declined and a vacuum formed in the root. Under drought condition, the dense stomas decreased and the upper epidermis keratinization, while the cortex thickness of root increased. The duct and vascular cylinder of L. hexandra was more sturdier than that of hydrophilic plant. All of the root length, root diameter, root project area and root volume increased under submerged condition, while only the root diameter significantly increased under waterlogged condition. In contrast, although the roots parameter was initially affected, it could recover the level of control with water stress being released. All in all, it was to useful understand the relation between L .hexandra and environment, especially how L. hexandra adapted to water stress.(3)In natural environment, the diurnal courses of air relative humidity (RH) surrounding leaves was higher both in June and in October, while the transpiration rate(Tr) was highest in April. The order of light use efficiency(LUE) was in October >in April >in June. The chlorophyll a (Chla) content in flooding condition was higher compared to the chlorophyll b (Chlb) content. The total chlorophyll content was higher compared to the control (0d) and ascended wavelike from the 0d in the period of submerged treatments. The Chla/Chlb ratio was 3:1 in natural environment, so it was under submerged condition. Not only the total chlorophyll content reduced under waterlogged condition, but also Chla/Chlb ratio steadily declined to lower value.(4) Both drought and flooding could result in the variation of photosynthetic character. Under submerged condition, the chlorophyll fluoresce parameters varied little, such as the coefficient of photochemical quantum(qP) and the effective photochemical quantum yield of PSⅡ(Yield).The photosynthesis of L. hexandra was not affected almost because its photosynthetic apparatus remained integrality by non-photochemical quantum (qN). But under waterlogged condition, the Yield values and qP values decreased obviously and the qP values was small. At the same time, the Yield values and qP values could recover the level of control with water stress being released, indicated that L. hexandra remained photosynthetic ability. Under drought condition, the Yield values and qP values first increased and then decreased, and the range of change was little. The qP values had a increasing trend. All results show that the physiological functions were not damaged because of qN avoiding the injury from superfluous light energy.(5) With the time of drought and waterlogged being prolonged, the activity of super-oxide dismutase (SOD) increased, higher 20% than control, but it was lower than control in the submerged treatments. Under water stress, the activity of peroxidase (POD) increased, and the order was the activity of peroxidase (POD) in leaf>that in stem>that in root. Especially under drought condition, the activity of peroxides (POD) in root was same as control. Furthermore the activity of cataloes (CAT) increased response to water stress, being 5th than control. As such the activity of dissocialitive praline (Pro) raised with drought stress. Comparation of the activity of dissociative proline(Pro) in roots,stems and leaves indicated it was different in the different parts. Pro value descended from on 40th days on the 30th days (highest), but higher than control. There was not significant difference between drought-dehydration and control. Under drought condition, all of the stem, root and leaf were affected by drought stress. Compared with stem and leaf, root was less injured from waterlogged condition. There was a system depressing the extent of peroxide and avoiding the damage resulting from overabundant moisture. (6)The endogenous hormones played an important role, which receipted the variation of internal or external environment, adjusted growth and remained normal state to resist water stress. The content of Eth first increased and then decreased under flooding condition, and the value under submerged condition was higher than that under waterlogged condition. In the early period of water stress, both the content of IAA and GA3 increased obviously. By contrast, the content of ABA first increased and then decreased, higher than control. With flooding stress being released, the content of IAA and ABA decreased, yet higher than control. The concentration of endogenous hormones was an important factor, whether promoting or restraining plant growth.(7)Usually plant owned the specific reproduce strategy to adopt all kinds of different environment in its life history. Without any pretreatments, the potentional livingness of L. hexandra seeds was near 69.5%, but germination rate was lower, only 3.8%. The average ratio of rhizomes with new bud appearance was 82.5% under the normal condition. Annual increases of tiller number and accumulated height of L. hexandra populations established in different years was significantly different. We supported that there was a physiologic dormancy and it was a perfect ways to reproduce L. hexandra by rhizomes germination.In conclusion, the plant adaptability to stress was determined by its traits and its surrounding environment. The systems of L. hexandra about photosynthesis, enzyme and physiological growth adjustment could vary along with water stress. After stress being released, the metabolize intensity could recovery the level of control. Furthermore, L. hexandra exhibited a higher reproductive effort that might be good at surviving and multiplying. In a word, L. hexandra was an ideal plant to conserve soil and water in the water-fluctuation belt such as rivers or lakes. For the development and application of L. hexandra, further studies on the mechanism of stress resistance, especially the transportation, anabolism and reciprocity of endogenous hormones by way of external hormones are needed. And study about the molecular mechanism and genetic basis is also needed.更多还原