【作者】 李甜江；

【导师】 李根前；

【作者基本信息】 北京林业大学 ， 森林培育， 2011， 博士

【摘要】 中国沙棘(Hippophae rhamnoides subsp, sinensis)是我国北方干旱、半干旱地区优良的多用途树种,克隆习性又赋予它“独木成林”和“永生的潜力”,在生态环境建设和林业产业发展中具有极其重要的作用。然而,其人工林近年来出现了大片衰退甚至死亡现象,原因在于连续干旱且随着林分的生长使土壤水分形成了负平衡所致。目前,关于衰退现象和病虫危害的报道较多,而衰退机制的研究极为零散。为此,本项目以不同立地类型样地及田间不同灌水强度形成土壤水分梯度,分析种群数量、种群结构、繁殖能力、生物量及其分配、光合速率以及活性氧自由基、丙二醛与土壤含水量(灌水强度)的关系,期望从生态、生理(生化)层次探讨干旱胁迫对种群衰退(衰老)的作用机制,丰富克隆植物及森林衰退的研究内容,并为其造林设计、森林经营及种群恢复提供依据。通过研究,得到了以下主要结果。(1)在毛乌素沙地和黄土高原,干旱胁迫是导致中国沙棘人工林衰退的主导因子。在毛乌素沙地,地处下湿地天然林的寿命可达50a以上,且此时还能通过林窗更新、林缘扩散继续维持种群的稳定性；而地处迎风坡的人工林,在8a时年龄结构已经成为衰退型。虽说天然林的土壤水分、有机质及氮含量均显著高于人工林,但逐步回归只有土壤含水量被选入方程,且决定系数高达85%以上。田间试验结果进一步表明,中国沙棘生长和繁殖能力最大时的灌水量为900mm-1050mm,相当于试区降水量的3.0倍-3.5倍。在黄土高原,土壤含水量按照北坡、西坡、峁顶、东坡、南坡的顺序依次下降,种群稳定性及种群增长率也按此顺序降低。林龄8a时,北坡和西坡尚处于增长阶段,峁顶和东坡种群处于稳定阶段,而南坡种群已经成为衰退型。因此,在降水不足的情况下,种群的演替方向取决于林地土壤含水量。(2)与天然林相比,中国沙棘人工林不仅土壤水分及养分含量、生产力、物种多样性低,而且种群繁殖能力下降、分株寿命缩短。其中,干旱胁迫造成繁殖和生长能力下降是种群衰退的根本原因,即种群因为不能自我更新而衰退。在不同立地条件下,由于土壤含水量差异导致繁殖和生长能力改变,从而影响种群的稳定性和分株寿命。在毛乌素沙地,下湿地天然林的繁殖能力、生长能力、分株寿命及种群稳定性均明显高于迎风坡人工林。且以人工林繁殖能力、生长能力及种群稳定性而言,丘间地高于迎风坡、洼地高于平地。田间试验结果进一步表明,当灌水强度为900mm～1050mm(相当于试区降水量的3.0倍～3.5倍)时种群的繁殖能力和生长能力达到最高值。在黄土高原,种群的繁殖能力、生长能力与土壤含水量呈正相关关系。因此在降水不足的情况下,如果造林地土壤含水量不能满足中国沙棘生长和繁殖的需要,干旱胁迫必将导致种群早衰。(3)在不同的水分条件下,中国沙棘通过生物量投资与分配调节在生长(存活)与繁殖之间做出权衡,从而维持克隆的持久性与种群的稳定性。其中,种群生长和繁殖能力与种群及其构件的生物量投资、树干及克隆器官的生物量分配比例呈正相关关系,与枝条、垂直根生物量分配比例呈负相关关系；而种群及其构件生物量投资、树干及克隆器官生物量分配与灌水强度呈凸形抛物线关系,枝条及垂直根生物量分配与灌水强度呈凹形抛物线关系。因此,在水分适宜的情况下,中国沙棘加大对种群及其构件生物量的投资、加大对树干及克隆器官的生物量分配,种群生长和繁殖能力得到充分发挥；在干旱缺水的情况下,种群将更多的生物量分配于垂直根系的发育,以获取更多的土壤水分和养分资源促进现有植株的存活或生长,这样势必降低种群的生长和繁殖能力。(4)灌水通过改变植物组织含水量影响光合生理特征及水分生理特征,光合生理特征及水分生理特征的改变影响种群生物量投资及分配格局,种群通过生物量投资及分配格局调节形成与水分资源供应水平相适应的行为特征,尤其是通过生长(存活)与繁殖之间的权衡维持克隆的持久性及种群的稳定性。在高水分条件下,组织含水量提高,光合速率上升、丙二醛及超氧自由基含量下降,种群对树干及克隆器官的生物量投资和分配加大,生长和繁殖能力得到充分展示。因此,种群以个体高大、分布密集为特征,有利于克隆持久性和种群稳定性的维持。在低水分条件下,叶片及根系含水量降低,光合速率下降、丙二醛及超氧自由基含量上升,种群对枝条及根系的生物量投资和分配加大、对树干及克隆的生物量投资和分配减小,生长和繁殖能力受到抑制。因此,种群以个体矮小、分布稀疏为特征,有利于提高分株的存活与生长概率,但克隆持久性和种群稳定性将受到影响。更多还原

【Abstract】 As excellent Multiple Purpose Tree in arid semi-arid areas, and with powerful feature of cloning, Hippophae rhamnoides L. subsp. Sinensis has been playing a significant role in the ecological environment building and forestry industry development. However, some plantations have suffered a large-scale declination even death in recent years due to a negative balance of soil moisture caused by the continuous drought and the forest growth. There are many reports about decline phenomenon and pests but few about water mechanisms of decline. After experiments on different site types and with different soil moisture conditions thanks to different irrigation intensities, this paper tries to analyze the relationships between soil moisture and population density, population structure, clone breed ability, biomass allocation, photosynthesis, Malondialdehyde and reactive oxygen species, to reveal the water physio-ecology mechanism of decline plantation in drought stress in the perspective of ecology and physiology (biochemistry). It could enrich the study of clone plant and forest decline and provide basis for plantation design, forest management and recovery of species. And the main results and conclusions are introduced as below.(1) Drought press is proved the leading cause of the decline of planted Hippophae rhamnoides L. subsp. Sinensis on Mu Us Sandland and Loess Plateau, on Mu Us Sandland, the natural forest on lower site can live more than 50 years and maintain population increase or stability by gap regeneration and edge dispersal, while those on windward slope decline at 8a. Though natural forests possess more soil moisture, organic matter and nitrogen than plantation, it is the soil moisture that has been selected as a factor of the stepwise regression equation and has the determination coefficient of 85%. The field trials further show that Hippophae rhamnoides L. subsp. Sinensis grows faster and has better fertility when was irrigated by water of 900mm-1050mm,3.0-3.5 times more than the normal rainfall. On the Loess Plateau, the soil moisture decreases as well as the population stability and growth rate on northern slope, western slope, the top, eastern slope and southern slope in turn. The stability and growth rate of population decrease in turn. The forests of 8a keep growing on northern and western slope and maintain stable on the top area and on the eastern slope while those on the southern slope have show decline. Therefore, under the circumstance of lack of enough rainfall, it is the soil moisture on the forested area that decides the trend of community succession.(2) Compared with natural forest, Hippophae rhamnoides L. subsp. Sinensis possesses less soil moisture, nutrient content, productivity, biodiversity and lower fertility and shorter life expectance of ramet. Drought press leading to the decline of reproductive ability and growth is the fundamental cause of the population decline by interrupting the process of self restoration. The vary of soil moisture in different sites leads to the change of fertility and growing ability, and thus affects the population stability and life expectance of ramet. In Mu Us Sandland, natural forest shows advantages in reproductive ability, productivity, life expectance and population stability if compared with plantation. But the plantation forests on sand-dune performs better than those on the winward slope, on depression better than on the flatland in terms of reproductive ability, productivity and population stability. The field trials further show that Hippophae rhamnoides L. subsp. Sinensis grows faster and has better fertility when was irrigated by water of 900mm～1050mm,3.0-3.5 times more than the normal rainfall. On the Loess Plateau, the reproduction and production of the population are positively related with the soil moisture. So under the circumstance of lacking rainfall, drought press will lead to population decline if the soil moisture in forested area fails to meet the requirement of growth and reproduction of Hippophae rhamnoides L. subsp. Sinensis.(3) Under different water conditions Hippophae rhamnoides L. subsp. Sinensis must balance the survival against reproduction through biomass allocation and adjustment to maintain the persistence of clone and stability of population. The population growth and reproduction ability correlate positively with the biomass investment of the population and modular, biomass allocation rates among tree trunk and organ of cloning, while correlate negatively with biomass allocation rates between branch and vertical roots. The biomass investment of the population and stem, biomass allocation rates among tree trunk and organ of cloning have an inverted U-shaped relationship with the irrigation amount, while the biomass allocation rates between branch and vertical roots show a U-shape relationship with the latter. Therefore, with proper water condition, Hippophae rhamnoides L. subsp. Sinensis would performance better in population growth and reproductive ability if it invests more biomass in population and its stem and allocates more to the tree trunk and organ of cloning. Under the circumstance of drought and lack of water, the population would allocate more biomass to the growth of vertical roots to obtain more water and nutrient to maintain the survival and keep growing, which would surely decrease the population growth and fertility.(4) Through changing the water conditions of plant tissues, the irrigation would affect the photo-physiological and water physiology characteristics, of which changes would influence the population biomass investment and allocation status. The population then relatively forms certain behaviors to adapt to the water supply, which is to maintain the persistence of cloning and population stability by balancing between survival and reproduction. Under high moisture conditions, the increasing of soil moisture in plant tissues would lead to a rise in photosynthetic rate and decrease in MAD and reactive oxygen species radicals, the population invest and allocate more biomass to the organs of cloning, which the whole process will benefit the productivity and reproduction. Therefore, population with higher plant height and intensive distribution would be good for the persistence of cloning and population stability. In contrast, low moisture conditions would depress the productivity and fertility. It is concluded that the population with short plants and scattered distribution would help the survival and growing rates but negatively affect the persistence of cloning and population stability.更多还原