水盾草入侵沉水植物群落的季节动态

The seasonal dynamics of the submerged plant communities invaded by Cabomba caroliniana gray

水盾草 (Cabomba caroliniana)是原产美国和南美巴西等地的多年生植物。自 1993年作为新记录报道以来 ,在中国华东水网地带大面积扩散 ,并在江苏太湖流域、浙江杭嘉湖平原、宁绍平原等水域成为很多沉水植物群落的优势种。课题组在其分布区的苏州太湖乡、湖州道场乡、杭州五常乡、绍兴陶堰镇、柯岩镇和宁波方桥镇等 6个地点设置固定样地对水盾草入侵群落进行了9个季节的调查 ,分析了不同季节群落种类组成与生物量的变化等。结果表明 :各群落优势种在不同季节有变化 ,有些群落在所调查季节中主要优势种都为水盾草 (五常乡、柯岩镇和方桥镇 ) ,另一些群落优势种则发生季节及年际变化 (太湖乡、道场乡和陶堰镇 ) ,如太湖乡冬季优势种均为菹草、其它季节为水盾草。水盾草的生物量在样地、季节间变化很大 ,最高一般在秋季 ,变幅达近 5 0倍。水盾草生物量的季节动态显示 3种情况 :一是由于人为干扰大幅下降 ,二是处于相对稳定的平衡状态 ,三是大幅上升。其中后两种情况下人为干扰较小 ,是群落自身演替的结果。从种类组成来看 ,种类组成单一的群落 ,水盾草重要值均在 5 0 %以上 ;种类组成复杂的群落 ,其重要值随季节而变化。说明群落物种丰度与其对水盾草的易感性间有较密切的联系 ,水盾草易于入侵组成单一的群?

Cabomba caroliniana (cabomba, fanwort) is a perennial aquatic plant originated from the United States, Brazil and the other places of the South America. Since reported as a new record in 1993, Cabomba have been widely spread in the water bodies in the eastern China, and become dominant in the submerged plant communities of Taihu lake region in Jiangsu Province, Hangjiahu lake and Ningshao Plains in Zhejiang Province. Aiming at describing the seasonal dynamics of species composition and biomass of the communities invaded by Cabomba, six sites were investigated in Taihu (Suzhou), Daochang (Huzhou), Wuchang (Hangzhou), Taoyan (Shaoxing), Keyan (Shaoxing), and Fangqiao (Ningbo) using quadrat method in the nine seasons from the winter of 2000 to the winter of 2002. The results showed that, the dominant species of the communities were only occasionally changed with season in some places, including the communities in Taihu, Daochang, and Taoyan. Where Cabomba always dominated the Taihu community except it was replaced by Potamogeton crispus in winter seasons. However the biomass of Cabomba was varied remarkably among sites and seasons, the scale was as large as 50 times, and the peak was normally occurred in autumn. The seasonal dynamics of Cabomba biomass showed three kinds of regularities, the rapidly decreasing, relatively stable, and greatly increasing. Where the last two trends were the result of community succession with a relatively low level of human disturbance. The dominance of Cabomba was also changed with season, however it kept in a high level (importance value >50%) if the community was simple in species composition. Which means species simple communities can be easily invaded and quickly dominated by Cabomba. The maximum biomass of native species and Cabomba were occurred in different depth of water. The suitable depth for Cabomba was approximately 1.6 meters, while it was approximately (0.8)～(1.0) meters for native species (Ceratophyllum demersum, Vallisneria natans and Hydrilla verticillata, etc.). The suitable depth of Cabomba was always deeper than that of native species with the season changed, which means Cabomba can occupy a unique niche in the submerged plant communities. The two reasons for the successful invasion of Cabomba, we can conclude from our study from the aspect of community ecology, might be the low species diversity and the vacancy of spatial niche in the community. Some artificial methods may be effective to Cabomba control accordingly, such as the clearing away of the silt, but it will threaten the existence of native species as well.