【作者】 靳瑰丽；

【导师】 朱进忠；

【作者基本信息】 新疆农业大学 ， 草业科学， 2009， 博士

【摘要】 伊犁绢蒿(Seriphidium transiliense)荒漠草地属于中亚气候型荒漠,在我国仅分布于新疆。该类草地生态系统脆弱,却仍然担负着极大的放牧压力,再加上人为破坏严重及保护意识低下,成为退化较为普遍、严重的地段。对草地生物多样性的保护,畜牧业生产和绿洲生态安全造成了严重威胁。本研究采用以空间序列代替时间序列的研究方法,探讨伊犁绢蒿荒漠草地退化演替序列划分方法,研究在退化过程中植物群落、土壤种子库、营养物质、生理机能方面的组织调节能力,明确其生态适应对策,评价生态系统的风险性。为全面理解草地退化机理,适时制定生态系统恢复及可持续利用方案提供理论及现实依据。主要研究结果如下:(1)伊犁绢蒿荒漠退化草地演替序列划分方法运用TWINSPAN分类,结合DCA和DCCA排序,将研究区伊犁绢蒿荒漠草地划分为5个演替阶段,即未退化阶段(Ⅰ)、中度退化阶段(Ⅱ)、重度退化阶段(Ⅲ)、极度退化阶段(Ⅳ)和系统崩溃阶段(Ⅴ)。DCA排序对退化演替序列从受害程度和抵御胁迫能力两个方面进行了解释,DCCA排序对退化演替序列从土壤理化性质方面进行了环境解释。(2)伊犁绢蒿荒漠退化草地植物群落生态适应对策随着退化演替的增强,在个体水平上,主要物种伊犁绢蒿、叉毛蓬(Petrosimonia sibirica)、角果藜(Ceratocarpus arenarius),弯果胡卢巴(Trigonella arcuata)、伊犁郁金香(Tulipa iliensis)、腋球顶冰花(Gagea bulbifera)和串珠老鹳草(Geranium transversale)的株体形态均趋于小型化,形成避食性的生态适应对策;在种群水平上,主要通过调整繁殖策略来适应逆境胁迫,形成不同种群在不同退化阶段的生态适应对策;在群落水平上,通过增加物种数提高植物竞争性,筛选繁殖能力强、耐牧性和避牧性高的植物作为优势种来适应放牧胁迫,这一适应对策导致群落主要植物种发生消长变化,原生植被丧失,群落经历量变、量变与质变交互、质变的生态适应过程。(3)伊犁绢蒿荒漠退化草地土壤种子库生态适应对策土壤种子库表现出应用良好雨水条件迅速萌发的生态适应对策,并且具有留存部分种子以应对外界干扰的生态保险机制。多样性测度结果表明,种子库植物多样性变化符合中度干扰理论,但短暂土壤种子库多样性大于持久土壤种子库,且波动性较大;物种替代速度一般在退化初期和后期较大,从而形成了未退化向退化,退化向系统崩溃阶段的跃迁;各演替阶段土壤种子库相似性较小,相似性系数在0.22~0.34之间,表现出种子库因地上植被的退化而形成不稳定性。持久土壤种子库密度总体呈下降趋势,其规律是Ⅰ>Ⅳ=Ⅴ>Ⅱ>Ⅲ;而短暂土壤种子库密度总体呈增加趋势,其规律是Ⅳ>Ⅴ>Ⅲ>Ⅱ>Ⅰ。在垂直分布上,土壤种子库随退化演替的增强呈现浅层化,0～5cm土层的种子比例逐渐增大。两种土壤种子库与地上植被物种组成上均不相似,而短暂土壤种子库密度与地上植被密度存在极显著的正相关,其关系可以用二次曲线来描述。(4)伊犁绢蒿荒漠退化草地植物营养生态适应对策草地退化过程中,主要草地植物及群落各营养成分随植株个体构件、种群特征及群落组成的变化而波动。应用主成分分析法综合评价草地营养价值得出,随退化演替的增强,优势种伊犁绢蒿营养价值逐渐提高;次优势种叉毛蓬在各退化阶段的营养价值均低于未退化阶段,但在极度和系统崩溃阶段则有小幅度的提高;而植物群落的营养价值逐渐降低;表现出草地营养价值逐渐变劣。(5)伊犁绢蒿荒漠退化草地植物生理生态适应对策草地退化过程中,主要植物生理抗性指标均发生了一定变化,中度退化与未退化阶段之间的生理生态适应性相异系数较大,因此,植物生理变化先于个体、种群和群落外貌特征变化表现出来,中度退化阶段是植物生理受害的转折点。随草地退化演替的增强,植物表现出适应放牧胁迫的不同生理响应机制,伊犁绢蒿生理调节能力由强变弱,终因胁迫超过了调节限度而消亡,为忍耐型;叉毛蓬多数生理指标差异不显著,受损不突出,表现为适应放牧胁迫,为迟钝型;伊犁郁金香生理调节能力相对较差,随演替的加强而逐渐受损,为敏感型。(6)伊犁绢蒿荒漠退化草地生态风险评价随着退化演替的增强,伊犁绢蒿荒漠草地生态风险值逐渐变大,并且变化速率依次增加。将其划分为4个生态风险级,生态风险值>0.8030为一级风险,生态风险值0.0059～0.8030为二级风险,生态风险值0.0034～0.0059为三级风险,生态风险值<0.0034为四级风险,可针对风险阈值具体制定相应的草地恢复措施。更多还原

【Abstract】 Seriphidium transiliense desert grassland belongs to the climatic type desert of Central Asia, and distributed only in Xinjiang, the western region of China. This grassland ecosystem is too vulnerable, but still suffering heavy grazing pressure, furthermore, frequent anthropogenic destruction and lack of the public protection awareness which resulting the grassland severely degraded at large. These are seriously threatening the grassland biodiversity, livestock production and oasis ecological security. In this study, the approach for subdivision of degradation succession was explored by using the methodology of spatial sequence instead of temporal sequence, the organizational coordination capacity in terms of plant community, soil seed bank, nutrients, and physiological function during the process of grassland degradation was studied for clarifying its ecological adaptation strategy, assessing the ecosystem risk, and providing theoretical and practical basis on comprehensively understanding the mechanism of grassland degradation, timely conducting ecosystem restoration and sustainable utilization programs. The main results are as follows:(1) The Approach for Subdivision of the Degradation SuccessionBy TWINSPAN, DCA and DCCA, the S. transiliense desert grassland of the study area was subdivided into five successional stages, non-degraded stage (I), medium-degraded stage (II), heavy-degraded stage (III), over-degraded stage (IV), and system-collapse stage (V). The outputs of DCA provided interpretation on the degradation successional sequence from stress injury rate and resistibility, whereas the outputs of DCCA served as an environmental interpretation on degradation successional sequence from the soil physical and chemical properties.(2) The Ecological Adaptation Strategy of the Plant CommunityWith the intensity of grassland degradation, at individual level, the plant autoecology of main species, S. transiliense, Petrosimonia sibirica, Ceratocarpus arenarius, Trigonella arcuata, Tulipa iliensis, Gagea bulbifera, and Geranium transversale, tended to miniaturize for avoidance strategy. At the population level, the plant populations format their individual ecological adaptation strategy in different degraded stages, mainly through adjusting reproductive strategy to adapt the stress. At the community level, community adopts the ecological adaptation strategy of increasing the species number to enhance the competitiveness to filter the dominant species for adapting grazing stress, which possesses high reproductive capacity, grazing tolerance and resistance, but this often leads to main plant species changed and loss of the original vegetation. The plant community had experienced the ecological adaptation process from quantitative to qualitative change.(3) The Ecological Adaptation Strategy of the Soil Seed BankThe soil seed bank had the ecological adaptation strategy by taking advantage of rainfall conditions to germinate rapidly,and had an ecological insurance mechanism of retaining some seeds to resist external interference. The assessment of soil seed bank species diversity showed that its changes were in accordance with“medium disturbance theory”, the species diversity of transient seedbank was greater than that of persistent seedbank and with greater fluctuation. The substitution speed of plant species was higher in early and late stages of degradation process, thus accelerated the changes both from non-degraded stage to degraded stages and from degraded stages to system-collapse stage. The similarities of soil seed bank species diversity in different degraded stages were low from 0.22~0.34 respectively, indicating that all the seedbanks were unstable caused by the degraded aboveground vegetation. The density of persistent seedbank was generally decreased as I>IV=V>II>III, whereas the density of transient soil seed bank was generally increased as IV>V>III>II>I. In vertical distribution, the seed density in top layer (0~5cm) was increasing along with the grassland degradation process, indicating that the seeds tend to distribute in shallow soil. The species composition of the two types of seedbank was all dissimilar to that of aboveground vegetation. However, there was a very significant positive correlation between the densities of transient seedbank and aboveground vegetation that could be described by quadratic curve. (4) The Plant Nutritional Ecological Adaptation StrategyIn the process of grassland degradation, the changes of each nutrition component of the main plant species and community fluctuated with individual module, population characteristics and community composition. By PCA the nutrient values of the grassland plant were synthetically evaluated, the results showed that with the intensity of grassland degradation, the nutrient value of dominant species S. transiliense increased gradually, the nutrient value of sub-dominant species P. sibirica in each degraded stage was less than that of non-degraded stage, and nutrient value in latter degraded stages increased slightly compared with that of early degraded stages, the nutrient value of plant community decreased gradually, and the nutrient value of S. transiliense desert grassland became poor.(5) The Plant Physiological Ecological Adaptation StrategyIn the process of grassland degradation, the all physiological resistance indexes of the main grassland species changed, and the dissimilarity coefficient index was high beween non-degraded stage and medium-degraded stage. Therefore, the physiological changes happened prior to the appearance characteristics changes of individual, population and community. And medium-degraded stage was the turning point of plant physiological injury. The plants showed different physiological response mechanisms to grazing stress. The plants showed different physiological response mechanisms to grazing stress. With the intensity of grassland degradation, the physiological adjustment ability as followed, S. transiliense changed from strong to feeble, and died out as the grazing stress exceeding the adjustment limit, so it was the tolerance species, the most physiological resistance indexes of P. sibirica had no significant changes, without prominent injury and adapt to grazing stress, so it was the insusceptible species, the physiological adjustment ability of T. iliensis was relatively poor, and the injury increased gradually, so it was the susceptible species.(6) The Ecological Risk AssessmentWith the intensity of grassland degradation, the ecological risk level of S. transiliense desert grassland became higher and the change rate increased gradually. The risk was subdivided into four risk levels by the ecological risk value (Ri), viz. the first level risk (Ri >0.8030), the second level risk (Ri from 0.0059 to 0.8030), the third level risk (Ri from 0.0034 to 0.0059), and the fourth level risk (Ri <0.0034), with the reverse direction of succession. The specific restoration measures of degraded grassland should be formulated based on risk threshold accordingly.更多还原