三峡水库秭归段消落带植物群落特征及其与环境因子的关系

消落带植被群落特征及物种多样性的研究一直是植物生态学和恢复生态学研究的热点。三峡水库的运行对消落带生态系统造成了极大的影响,如引起绝大部分河岸带土著植物消失、生物多样性降低以及土壤侵蚀严重等一系列生态学问题。研究消落带植物群落特征及其影响机制,旨在丰富消落带新生湿地生态学研究内容,为消落带植被的恢复、湿地保护和管理提供科学依据。通过对三峡水库秭归段香溪河与童庄河陡坡消落带植物群落及其环境因子的实地调查,并结合双向聚类分析及典范对应分析(CCA),研究了三峡水库消落带植物群落特征、物种多样性及其与环境因子之间的关系。结果表明:(1)在三峡水库秭归段消落带共发现维管植物34种,隶属于15科32属,其中菊科(Compositae)和禾本科(Gramineae)种类数较多,为优势物种,植物群落组成以草本植物为主,一年生和多年生草本植物为23种和11种,分别占67.65%和32.35%,一年生植物占绝对优势;(2)随海拔升高,物种数、Shannon多样性指数、Pielou均匀度从低海拔到高海拔随着海拔的增加而升高,而Simpson优势度指数指数从低海拔到高海拔呈下降趋势;(3)双向聚类显示消落带...

Characteristics of plant communities and their relationships with environmental factors in the water level fluctuation zone of the Zigui region of the Three Gorges Reservoir

River systems around the globe are increasingly affected by damming to satisfy increasing demands for hydroelectricity, flood mitigation and reliable water supplies. The impoundment of the reservoirs can significantly alter river flow, shorelines, sediment and aquatic fauna and flora and can result in the loss of original riparian vegetation. After the first impoundment of the Three Gorges Reservoir (TGR) in June 2003 and the complete impoundment in 2010, the water level of the reservoir fluctuates from 145 m a.s.l in summer (May to September) to 175 m in winter (October to April), resulting in formation of the water level fluctuation zone (WLFZ) with a total area of 350 km² in the Reservoir. Compared with other reservoirs, the hydrological regime of the TGR is the exactly opposite of the natural flood rhythms of the Yangtze River with prolonged inundation duration (nearly half a year) and deep submergence depth (up to 30 m). The operation of the Three Gorges Reservoir had significant effects on the ecosystem of the riparian zone, causing a series of ecological problems such as the disappearance of original vegetation and reduced biodiversity in most of the riparian zone, as well as severe soil erosion. These changes might alter plant community characteristics in the WLFZ of the TGR. The study of plant community structure and species diversity in the WLFZ has been a research hotpot in plant ecology and restoration ecology. The purpose of studying the characteristics of plant communities and their influencing mechanisms in the WLFZ is to enrich the ecological research content of newborn wetlands, and to provide a scientific basis for the vegetation restoration, wetland protection and management in the WLFZ. The height, coverage and frequency of each plant species and the soil properties were measured at each elevation zone (145-155 m, 155-165 m, and 165-175 m) in the WFLZ of the Zigui region of the Three Gorges Reservoir (ZRTGR) in 2018. The two-way clustering analysis and canonical correspondence analysis (CCA) were used to analyze the spatial variations of the plant community characteristics and determine the key environmental factors influencing vegetation. The main results were as follows: (1) a total of 34 species of vascular plants, belonging to 15 families and 32 genera, were recorded in the WLFZ of the ZRTGR, with abundant species of Compositae and Gramineae. Vegetation was dominated by herbaceous plants amog which the annual herbs (i.e. Setaria viridis, Digitaria sanguinalis, Echinochloa crusgalli, Bidens pilosa, and Xanthium strumarium) and perennial herbs (i.e. Cynodon dactylon and Cyperus rotundus) accounted for 67.65% (23) and 32.35% (11) of the total number of species, respectively. (2) Species diversity showed an increasing trend with elevation and had significant differences between low, middle and high elevation area (P < 0.05). The species number, Shannon-Wiener diversity index, and Pielou evenness index of the plant community increased with the increasing elevation from the low to high elevation area, whilamonge the Simpson dominance index decreased with the increasing elevation. (3) Using two-way clustering analysis methods, the vegetation in the WLFZ consisted of three main plant community types: Ass. C. dactylon, Ass. S. viridis+D. sanguinalis and Ass. B. pilosa. The low and middle altitudes are dominated by monodominant community of C. dactylon, while the high altitudes are dominated by co-optimal communities of Setaria viridis, D. sanguinalis, B. pilosa and X. sibiricum. The CCA showed that elevation and flooding duration were the most important factors influencing the species composition of the plant community in the WLFZ, while TN and TK were the secondary important factors influencing the species distribution pattern of the community. The soil in the WLFZ was poor and limited by N and K nutrients. The diversity of plant communities in the reservoir area is still declining, which requires long-term monitoring and research of plant communities and environmental factors.