三峡水库蓄水对长江干流河岸植物组成的影响

三峡水库采取“冬蓄夏泄”的水位调度方式，导致淹没区的原河岸带和陆地植物及其群落的大量消失，并将逐渐形成适应消落带环境的植物群落。在忠县选择长江干流北岸典型区域建立固定样区，对蓄水前（2007年）后（2015年）158~173 m高程段植物组成变化进行研究。结果发现：（1）蓄水前，样区共有维管束植物106种（隶属47科96属），优势植物生活型为多年生草本、一年生草本和灌木；蓄水后维管束植物种类下降了45.28%，只有58种（隶属26科51属），其中多年生草本所占比例由蓄水前的40.57%上升为43.10%，一年生草本由蓄水前的28.30%上升为48.28%，灌木已不再是优势植物生活型。（2）蓄水后，狗牙根（Cynodon dactylon）的重要值由蓄水前的1.72%增大到45.06%，荩草（Arthraxon hispidus）和白茅（Imperata cylindrica）则由之前的6.81%和16.48%下降到0。样区下部的优势物种由蓄水前的荩草、白茅和喜旱莲子草（Alternanthera philoxeroides）变为狗牙根、稗（Echinochloa crusgalli）和水蓼（Polygonum hydropiper）；样区中部的优势物种由蓄水前的荩草和白茅变为狗牙根、苍耳（Xanthium sibiricum）、鬼针草（Bidens pilosa）和喜旱莲子草；样区上部的优势物种由蓄水前的白茅变为狗牙根、鬼针草和狗尾草（Setaria viridis）。（3）蓄水前，158~173 m物种数范围为42~66，各高程段物种数无明显变化趋势；蓄水后，158~173 m物种数范围为14~43，各高程段物种数差异明显，且呈现出随高程上升而增加的趋势，而物种多样性指数和物种均匀度指数均未随高程变化呈现出明显的变化趋势。研究表明，三峡水库运行导致消落带植物种类下降了近50%，许多不适应水淹的物种消失或优势度减小；一些克隆能力强的多年生草本竞争优势明显，部分种子扩散能力强的一年生草本依靠种子休眠的形式躲避冬季长期淹水，也能适应消落带这种特殊的生境；不同高程段消落带生态系统受淹水深度、淹水时间、淹水频率的影响不同，导致植物群落的物种组成和物种分布存在显著差异，特别是优势种变化明显。 关键词： 狗牙根；一年生草本；多年生草本；物种丰富度；水位变动

Effects of Three Gorges Dam on Riparian Vascular Plants of the Main Stream of Yangtze River

The construction of the Three Gorges Dam (TGD) has led to the disappearance of original plant species and communities,and new predominant plant communities had been formed to adapt the riparian zone environment changes.The study of predominant plant species distribution in those areas is important for the ecological restoration of Three Gorges Reservoir riparian zones.In this study,we investigated the plant species diversity before (2007) and after (2015) the dam impoundment at a special site in Zhong county,used populations Important Values(IVs) to estimate the relative importance of species of this area.The results showed that:(1) There werel06 vascular plant species (belong to 96 genera in 47 families) before the dam impoundment(2007),and Perennial herbs,annual herbs,and shrubs were co-dominated in this area.After dam impounding(2015),the vascular plant species dropped dramatically down to 58 (belonging to 51 genera in26 families),with shrub losing their dominated role.The perennial herbs percentages in all species increased from 40.57％ (2007) to 43.10％ (2015),while annual herbs percentages increased from 28.30％ to 48.28％,respectively.(2) The IVs of Cynodon dactylon increased from 1.72％ (2007) to 45.06％ (2015);while the IVs of Arthraxon hispidus and Imperata cylindrical decreased respectively from 6.81％ and 16.48％ to both zeros.The predominant species in the bottom of studied area changed from Arthraxon hispidus,Imperata cylindrical and Alternanthera philoxeroides to Cynodon dactylon,Echinochloa crusgalli and Polygonum hydropiper;the predominant species in the middle of studied area changed from Arthraxon hispidus and Imperata cylindrical to Cynodon dactylon,Xanthium sibiricum,Bidens pilosa and Alternanthera philoxeroides;and the top area predominant species changed from Imperata cylindrica to Cynodon dactylon,Xanthium sibiricum and Setaria viridis.(3) Before the dam impoundment in 2007,the plant species between elevation 158 m to 173 m were accounted as 42-66,and there were no obvious changes with the elevation variations.After the impoundment in 2015,the plant species between elevation 158 m and 173 m decreased to 14-43,and the species densities increased along the elevation increases.Meanwhile,the species diversity index and species evenness index didn' t show obvious changing trends along the elevation vairiations.The results suggested the dam impoundment had caused the plant species in the studied area decreased about 50％.Many species that couldn' t suffer the submergence had been vanishing or marginalizing.However,some perennials that have strong clone abilities showed obviously competitive preponderance and the annuals whose seeds had strong dispersal abilities could evade the winter submergences through seed dormancy and riparian habitats adaptation.The plants were affected by the difference of submergence depth,submergence time and submergence frequency,leading to the significant differences in species composition and distribution at different elevations,particularly for those predominant species changes.