摘要
种子库是植物群落的重要组成部分,是维持植被演替更新的物质基础,它能对植物群落所受到的灾难性破坏可以起到缓冲作用,减少种群灭绝的几率；同时土壤种子库还是植物响应土地利用和气候变化的重要指示者。通过研究土壤种子库不但可以评价退化系统的质量或预测植被的发展动态,还可为植被恢复的物种选择提供理论基础。本研究选取洞庭湖主要4种植被类型(芦苇+意杨、芦苇、苔草、荫草)及退田还湖工程示范区—青山垸为研究对象。通过对洞庭湖植被调查取样和室内种子库萌发试验比较分析,揭示了洞庭湖不同植被类型与湿地种子库的关系以及在不同水位梯度下植被恢复过程中湿地种子库与地表植被的关系。主要结果如下：
(1)洞庭湖湿地种子库密度特征
对不同植被类型及不同水位梯度土壤种子库分析表明,种子库的大小均受所处地理位置水文条件及地表植被的物种组成的影响。
研究发现,在不同水位梯度下种子库由于受水文因子的影响湿地种子库的密度表现出显著地差异性,呈“V”型结构,即低水位区与高水位区高,中水位区低。同时受地表植被物种组成的影响,在青山垸高水位区地表植被主要由1年生植物组成,由于长期适应湖区特定的生态环境,这些1年生植物都能在洪水前完成生命史,其种子成为种子库的主要来源,因此呈现出高水位区种子库密度大于中水位区。
(2)洞庭湖湿地种子库的垂直分布
通过对不同样区土壤种子不同土壤剖面层(0-2cm、2-5cm、5-10cm)的分析发现,土壤种子库中种子的垂直分布规律为表层(0-2cm)土壤中种子比例最高,随著土壤剖面深度的增加而递减。同时,研究表明,鱼类的活动和水文的波动也对种子库的垂直分布有着重要影响。
(3)洞庭湖湿地种子库与地表植被的相关性
通过对不同区域及不同植被类型湿地种子库的分析表明,在洞庭湖湿地种子库与地表植被相似性系数的高低与地表植被植物生活型密切相关,即1年生植物为主的区域其相似性系数也相对较高,而以多年生植物为主的区域二者相似性较
(4)湿地退化植被恢复重建的基本对策
首先是保护原有地表植被,减少人为干扰,以消除认为的破坏性干扰,逐步改善地表植被和生态小环境；同时通过调节恢复区水位的周期性变化,促进种子的输入,地表植被形成营造有利环境,构建群落,从而加速现有植被的次生演替。
As one of the important components in the plant communities, seed bank plays important roles in maintaining vegetation regeneration and succession, buffering the population extinction and indicating the changes of land utilization and global climate. Therefore, studying on the seed bank not only can evaluate the quality of the degradation ecosystem and predict the development dynamics of vegetation, but also can provide theoretics to the species selection for the vegetation resuming.
This paper focus on four kinds of vegetation in the Dongting Lake, and qingshanyuan which is a typical region of the project of "returning farmland into lake". Baseed on the investigation of the field vegetation in the Dongting Lake, the results of the indoor germination test of seed bank were analysised, the relationships betwwen the wetland seed banks and different vegetaion types were discussed, as well as the relationship between the seed bank and the characteristics of above-ground vegetations growing in different water levels were revealed. The results are as follows:
(1) The density characteristics of wetland seed bank at Dongting lake
The seed banks were significantly affected by the hydrological conditions and the composition of the above-ground vegetations. Result showed that the density of seed bank presents a "Ⅴ"-type structure, induced by the different water levels, which means that the low and high water level had higher seed bank densities than that of middle water level. Meanwhile, the seed bank was also significantly influenced by the composition of the surface vegetations. The surface vegetation in the high water level regions in the "Qingshanyuan" was mainly constituted with the annuals, which can complete their life history before the coming of flooding and the seeds of these plants whose seeds became the main source of the seed bank, therefore, the density of seed bank in the high water level region was larger than that of middle water level.
(2) The vertical distribution of the wetland seed bank at Dongting lake
The densities of seed bank among different regions with different soil profiles (0-2cm,2-5cm,5-10cm) were also studied in this paper. The results showed that the density decreased significantly according with the increase of the soil depth, which is highest in the soil surface (0-2cm). Meanwhile, we also found that the activities of fish and the hydrological fluctuations play an important role in affecting the vertical distribution of the seed bank.
(3) The relationship between the seed bank and the above-ground vegetations at Dongting lake
The similarity index between the seed bank and the surface vegetation is significantly related to the life-form of the vegetation, which was higher in the regions mianly composed of annuals and lower in the perennial vegetaions.
(4) The basic countermeasure about restoration and reconstruction of degraded vegetation of wetland
Due to the species richness and the complexity of community structure, it could be very important to pay attention to the protection of current above-ground vegetations and to rational guidance for human disturbances. At the same time, the seeds were importated and enabling environment to formation of ground vegetation were created because of regulating the resumption of cyclical changes in water level, and resulted in speeding up the existing vegetation secondary succession.
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