【作者】 韩路；

【导师】 宇振荣；

【作者基本信息】 中国农业大学 ， 生态学， 2014， 博士

【摘要】 干旱区水分制约着物种的形成、进化、演替和分布。以塔里木河上游荒漠河岸林植物群落为研究对象,通过样地调查与定位监测及室内分析,综合应用数量生态学、生态位理论、生物统计学与地统计学从植被生态学角度分析并探讨上游荒漠河岸林的植物区系、群落结构与空间格局、种间联结性及物种多样性、种群生态位、群落排序、群落动态的生态过程与演化机制、群落结构稳定的维持机制与优势种群保护措施。主要研究结果如下：1、塔里木河上游荒漠河岸林植物群落结构与物种组成简单,分层明显；区系地理成分以温带成分为主,物种多样性低、以矮小型高位芽植物占优势,以胡杨、灰胡杨与柽柳为群落建群种,物种组成与分布差异是是植物长期适应干旱荒漠环境的演化结果。分布格局以河流为中心向外依次形成郁闭度与年龄结构明显不同的林分与群落类型。物种分布极不均匀和高度的空间异质性,群落不稳定、植被发生分化和演替的趋势。2、上游荒漠河岸林群落结构与数量特征沿地下水位梯度递减,优势种衰弱,生活型功能群组成与植物水分生态功能群改变。植被盖度受损是在草本植物受损开始。退化过程中优势种的优势地位没有变化,植被稀疏化、留存物种的早生化是塔里木河上游植物群落退化的明显特征。植被密度、盖度与优势种群冠幅可作为地下水位变化的直观指标。3、上游荒漠河岸林群落主要物种间生态位重叠较大,负关联显著,种间竞争排斥导致群落组织结构水平低并限制群落物种共存。优势种对荒漠干旱环境具有较宽的生态幅与资源竞争利用能力,这是其成为群落优势种和分布较广的原因。群落相异性与生境异质性增大,群落多样性受损于草本层多样性。群落多样性受损的地下水位为4.0m,临界地下水位为5.5m。水分成为物种生存竞争的关键资源和驱动群落逆行演替、种群衰退的主要动力。4、研究荒漠河岸林乔木种间竞争的最佳邻体干扰范围为6m和荒漠河岸林空间分布的格局规模大小为5m×5m及优势种群在胸径达到20cm之前进行适当的人工疏伐竞争是导致群落结构、空间格局动态及分异格局形成的原因之一。5、上游荒漠河岸林土壤水分主要来源于河水入渗与浅层地下水的上升,其变异主要受结构性因素影响,空间上呈条带状格局,从北→南呈逐渐递减的分异规律。土壤有机质、全量与速效养分(N、P、K)较低,土壤变粗沙化,结构质地变劣,土壤生态功能减弱。土壤盐分表聚明显,地下水化学类型为Ca2+-Mg2+-Cl-型水为主。土壤水分与有机质明显影响植被盖度、物种多样性。土壤水分对植物群落的影响首先是减少了荒漠植物种的丰富度,进而威胁到种群规模,最终导致植被盖度下降。6、乔—灌—草群落阶段是群落演化的初始阶段,群落与环境退化过程表现为草本退化期、灌木退化期、乔木退化期。地下水位是所有环境因子中对植物群落分布起决定性作用的因子,其次为土壤水分与有机质。7、塔里木河上游中、下段胡杨种群结构为增长型,灰胡杨种群结构为衰退型,随河流走向种群逐渐消失。种群自疏指数接近-3/2,均为前期薄弱、后期衰退的濒危物种,灰胡杨种群衰退速度大于胡杨,未来种群将加速衰退。种群空间格局随发育进程从幼树→大树总体上是从集群→随机分布,显示出扩散的趋势,其是物种竞争和立地条件相互作用的结果。未来保持适当的人工辅助恢复措施和加强保护现有植株及其生境是保持优势种群自然更新和进行种群恢复的关键。8、提出半致死地下水位(GDW5。)作为群落退化的指标。上游荒漠河岸林维持较高物种多样性和植被正常生长的合理生态水位<4m,植被明显受损和群落退化的临界地下位为5.5m。保持合理的生态水位则是维持荒漠河岸林生态系统稳定的有效途径。更多还原

【Abstract】 Water is an important factor limiting the speciation, evolution, succession and distribution in arid areas.The plant community of desert riparian forest in the upper reaches of Tarim River as the research object,3sections,4sample strips and permanent large-scale plots were be established with field investigation, long-term monitoring, and soil chemical analysis. The flora, community structure and spatial pattern, interspecific association, biodiversity, ecological niche, gradient alalysis, ecological process and successive mechanism of desert riparian forest were studied and maintenance mechanism of community structure stability and protection measures of dominant population were discussed. The research was based on the theory and methods in floristic geography, quantitative ecology, mathematics statistics, geostatistics and ecological niche theory.The main obtained results are as follows:1The plant community structure and species composition were simple and stratification was obvious. The flora had an overwhelming number of temperate elements and life form was dominated by dwarf, small phaeneraphyte. P.euphratica, P.pruinosa and Tamarix ramosissima were constructive species, the species composition and distribution difference were the evolution result of plants adapting to the dry desert environment for a long time. Community distribution formed different forest stand and community types along the river center to the outside with different canopy density and age structures. Species distribution randomness and high spatial heterogeneity showed community was not stable and vegetation happened succession.2Community quantitative feature decreased obviously along the gradients of groundwater levels and dominant populations declined, life form functional group composition and plant water ecological function changed. The decrease of vegetation coverage was due to decline of herbaceous coverage. Dominant species retained its dominant position in the process of degradation. Degradation order was herb→shrub→woody and surviving species with strongly drough-enduring ability and spatseness was obvious feature. Vegetation density, coverage and crown width of dominant species could be as indicator of groundwater change.3The main species had higher niche overlaps and significant negative association, interspecific competition and repulsion leaded to the low level of organization structure and limited the species coexistence. Dominant species had wide ecological amplitude and competition ability for resources utilization to low water and nutrient soil, this was the cause for wide distribution. Community dissimilarity and habitat heterogeneity expanded, the decrease of species diversity was due to decline of herbaceous diversity. Degradation of species diversity happened at the4.0m and threshold at5.5m of groundwater depths. Groundwater level decrease was the main force to drive community succession, population decline and restrict population regeneration. 4Optimal competition range of objective tree was six meters in woody and pattern scale was5mx5m in desert plant community, and artificial thinning should be applied DBH<20cm of dominant population. Interspecific competition was the one of force to drive dynamic of spatial pattern and formation of differentiation pattern of dominant population.5The soil water mainly came from runoff infiltration and the rise of shallow groundwater, and its variation was mainly affected by structural factors. Spatial distribution of soil water content was banded structure and decreased gradually from north to south direct. Soil organic matter and total amount of nutrient were low and soil texture turned worse and soil coarsen and ecological function of soil decreased. Soil salt accumulated on surface soil and hydrochemistry type of groundwater were dominated by Ca2+-Mg2+-Cl-.The soil water content and organic matter affect obviously vegetation coverage, species diversity. Soil water content decreased the species abundance of desert plant, further decreased population size, eventually led to decrease of vegetation coverage.6The structure of woody, shrub and herb was the initial stage of community succession. The desert community degraded with the order:herb stage, shrub stage and woody stage.The groundwater level was the key factor of all environmental factor to affect the distribution pattern of plant community, secondy was soil water content and organic matter.7Structure of P.euphratica population were expanding type in middle and low sections and P.pruinosa were declining types in the upper reaches of Tarim River, it tended to decline and die out gradually along the river. The value of self-thinning of populations were close to-3/2and they were endangered plant. P.pruinosa had higher degradation rate than P.euphratica, and analysis of time sequence prediction indicated dominant population declined fastly in the future. The distribution patterns of dominant population changed from clumped to random pattern during development stage, appearing diffusion trend. This result was the interaction between competition and habitat. Protection of existing living trees and their habitats are important to the sustainable development of dominant population in the upper reaches of the Tarim River.8The half lethal underground water level (GDW50) was as a community degradation index.The rational ecological groundwater level for vegeation normal growth and maintenance high biodiversity was<4m and the threshold of groundwater depth for communit degradation was about5.5m.This could be used as a basin theory for vegetation restoration and ecological water transportation. In brief, keeping the rational ecological groundwater level was the effective path to sustain desert ecosystem stability.更多还原