三峡库区消落带水淹初期土壤种子库月份动态

干湿交替往往导致土壤种子库产生剧烈变化，严重影响着地上植被的自然恢复和生长。采用垂直空间梯度代替水淹时间梯度，研究了消落带水淹初期土壤种子库月份动态变化。结果表明：消落带内不同土地环境类型土壤种子库具有不同的月份变化趋势，分别是采伐迹地土壤种子库密度逐渐增加，弃耕地则逐渐降低。随着垂直空间梯度的升高，5、7、9月份消落带土壤种子库密度都表现为逐渐增加，说明水淹时间越长越不利于土壤种子的储存。不同月份共同出现的优势物种包括地果、黄鹌菜、具芒碎米莎草、毛马唐、婆婆纳、匍茎通泉草、鼠曲草、水田碎米荠、雾水葛、细穗腹水草、香附子、一年蓬、知风草、苎麻，这些物种构成了消落带土壤种子库的主要组成部分。各月份土壤种子库的物种生活型非常接近，主要以一年生草本和多年生草本为主，相对缺少乔灌木，且生活型百分比例在不同海拔梯度存在差异。结合土壤种子库物种水分生态功能，将其划分为湿生植物、湿中生植物、中生植物、旱中生植物，发现其主要以中生植物为主，高海拔区段旱中生植物比例相对较高，低海拔区段湿中生植物比例相对较高，而湿生植物比例则变化较小，水淹导致种子库植物呈现向中生和湿中生植物类型的变化趋势。消落带土壤种子库植物具有较高的生物多样性，但不同海拔区段植物变异性较高，没有形成绝对优势的物种，植被群落明显处于演替早期。研究认为，消落带水淹初期，土壤生境、物种组成以及种子储量都发生着剧烈的变化，仅依靠土壤种子库进行消落带植被恢复与重建是不现实的，必须要给予更多的人为干预。

Monthly dynamic variation of soil seed bank in water-level-fluctuating zone of Three Gorges Reservoir at the beginning after charging water

The periodical fluctuation of water-level-fluctuating zone in Three Gorges Reservoir led to the variation of the soil ecological environment between wet and dry state. This variation inevitably produce a greater change in the soil seed bank, which further affects the standing vegetation recovery and growth. In this paper, we studied the dynamic variation of soil seed bank in water-level-fluctuating zone of Three Gorges Reservoir at the beginning after charging water was studied by substituting flooding time gradient with vertical space gradient. As soil seed bank density of clear-cutting land increased gradually with time, the density of abandoned farmland decreased. With the vertical space gradient increasing, density of soil seed bank in water-level-fluctuating zone in May, July, September showed gradual increasing trend respectively. The above results suggested that the longer flooding dures, the smaller soil seeds storage amount is. Co-occuring dominant species in different months , including Ficus tikoua, Youngla japonica, Cyperus microiria, Digitaria chrysoblephara, Veronica didyma, Mazus miquelii, Gnaphalium affine, Cardamine lyrata, Pouzolzia zeylanica, Veronicastrum stenostachyum, Cyperus rotundus, Erigeron annuus, Eragrostis ferruginea and Boehmeria nivea, were main components of soil seed bank. These species had a strong adaptability to the fluctuating environmental changes. The life-form composition of soil seed bank in different months was very similar. They were mainly composed of seeds of annual and perennial herbs, while being relatively lack of the seeds of shrub and arbor. Moreover, the life form composition proportions of soil seed banks of different altitude space were different. Combining with water ecological function of the soil seed bank, we can divided it into hygrophytes, hygromesophytes, mesophytes and mesoxerophytes. They were mainly mesophytes based, the proportion of mesoxerophytes in high-altitude section and that of hygromesophytes in low altitudes of were relatively high, while the proportion of hygrophytes in different altitude section in different months changes only a little. This indicated water flooded caused mesophytes and hygromesophytes gradually increasing in the soil seed bank, which was also the change trend of plant water ecological function type in water-level-fluctuating zone. The plants in soil seed bank had higher biological diversity as well as the plant species was high variable in different elevation sections and was lack of absolute dominant species. The vegetation communities were obviously in its early succession stage. In conclusion, from the results of the soil seed bank of water-level-fluctuating zone in Three Gorges Reservoir, vegetation restoration and reconstruction of the potential were unrealistic. This suggested that the changes of habitat, spesies composition and seed reserves of the soil seed bank were drastic at the beginning after charging water. In order to restore the vegetation of water-level-fluctuating zone more quickly, more manual intervention need to be introduced rather than only depending on the original ones.