Comparison of plant diversity and community assembly between drawdown zone of Three Gorges Reservoir and its southwest reservoir area

Abstract

近年来,我国西南流域陆续建成多座梯级高坝大库工程,随之形成的大面积水库消落带面临着植物恢复等问题,能否借鉴三峡库区消落带已有的大量植物修复成果和经验尚缺乏科学依据。通过对2021年出露期三峡库区和西南库区消落带现存植物进行调查,采用淹水时间统一划分淹水梯度带, 淹水时间7个月及以上为重度淹水区(S)、淹水时间为5~6个月为中度淹水区(M)和淹水时间4个月及以下为轻度淹水区(L),定量比较了三峡库区和西南库区消落带沿各淹水梯度的物种组成、物种多样性和系统发育多样性,探讨了水库消落带物种组成的驱动因子、植物群落构建策略以及多样性维持机制等。结果显示,三峡库区消落带共发现维管束植物20科36属36种,西南库区消落带共发现维管束植物21科41属45种,二者物种组成的Jaccard、Sorensen相似性系数分别为30.65%、46.91%,均以一年生为主要生活型、菊科和禾本科为优势科,相似的淹水时间可能是导致二者物种组成相似的主要因素;西南库区消落带的Gleason丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数和Pielou均匀度指数整体优于三峡库区消落带,二者物种多样性均与淹水时间呈负相关,物种多样性的维持可能受环境筛选、种子扩散限制、生境异质性和区域种库的联合作用;三峡和西南库区消落带的群落系统发育水平均较低,也与淹水时间呈负相关,前者增长幅度更大,至L段系统发育水平已显著高于后者;除西南库区L段谱系结构无明显趋势外,三峡库区和西南库区消落带在整体水平上和在各淹水梯度段,植被谱系结构呈发散趋势,主要由远缘种组成,群落构建由随机过程主导。;In recent years, a number of high dams and reservoirs have been built in the southwestern basin of China, and the resulting large-area reservoir drawdown zone or water-level-fluctuating zone (WLFZ) is facing problems such as plant restoration. Scientific basis to draw lessons from the existing achievements and experiences of phytoremediation in the Three Gorges Reservoir (TGR) still lacks. Based on the investigation of the existing plants in the WLFZ of the TGR and the Southwest Reservoir during the emergence period in 2021, the WLFZ was divided according to the flooding time, severe flooded areas (S) with a flooding time of 7 months or more, moderate flooded areas (M) with a flooding time of 5 to 6 months, and light flooded areas (L) with a flooding time of 4 months or less. The species composition, species diversity and phylogenetic diversity of the WLFZ of the TGR and the Southwest Reservoir along each flooding gradient were quantitatively compared. The driving factors of species composition, plant community assembly strategy and diversity maintenance mechanism of the WLFZ of the reservoirs were discussed. The results showed that 36 species of vascular plants, belonging to 20 families and 36 genera, were found in the WLFZ of the TGR, and 45 vascular plant species belonging to 21 families and 41 genera recorded in the WLFZ of the Southwest Reservoir. The Jaccard and Sorensen similarity coefficients of species composition in the TGR and southwest areas were 30.65% and 46.91%, respectively, with annual as the main life form and Compositae and Gramineae as the dominant families. Similar flooding time may be the main factor leading to the similarity of species composition between the two regions. The Gleason richness index, Shannon-Wiener complexity index, Simpson dominance index and Pielou evenness index in the southwest study area were better than those in the TGR area. The species diversity of the two areas increased with flooding degree decrease. Species diversity may be maintained by a combination of environmental filtering, seed dispersal limitation, habitat heterogeneity and region species pool. The phylogeny level of community in the TGR and southwest study area was low, and negatively correlated with flooding time. The former increased more, and the phylogeny level of L section was significantly higher than the latter. In addition to the no obvious trend in the L section of the southwest study area, the vegetation phylogenetic structure of the TGR and the southwest study area is divergent at the overall level and in each flooding gradient section, mainly composed of distant species, and the community assembly is dominated by random processes.