三峡库区9种植物种子萌发特性及其在植被恢复中的意义

三峡大坝蓄水后形成的库区消涨带面临植被消亡、生态退化等问题。为了筛选出适用于库区消涨带植被恢复的植物, 将9种1年生植物种子放置在库区消涨带不同海拔进行水淹(W 165-8 m, 121 d;W 155-18 m, 230 d;W 147-26 m, 271 d), 然后在实验室条件下进行萌发, 研究在消涨带淹水胁迫下这些种子的萌发特性。结果表明: (1) 除马唐(Digitaria sanguinalis)、小蓬草(Conyza canadensis)、金色狗尾草(Setaria glauca)种子在各条件下萌发率都较低外, 不同水淹条件对萌发率影响不同: 与新鲜种子相比, W 165水淹后, 旱稗(Echinochloa hispidula)和婆婆针(Bidens bipinnata)种子萌发率显著上升, 其余种子萌发率均显著下降; W 155水淹后, 所有种子的萌发率都显著下降且只有鱧肠(Eclipta prostrate)、黄花蒿(Artemisia annua)、合萌(Aeschynomene indica)3个物种有萌发, 萌发率分别为11.0%、7.3%和2.7%; W 147水淹后, 旱稗和婆婆针种子萌发率显著上升, 鱧肠种子无显著差异, 其余种子萌发率显著下降。(2) 鱧肠、黄花蒿、婆婆针和旱稗种子比其它物种更耐水淹。W 165水淹后, 鱧肠、黄花蒿、婆婆针、旱稗种子萌发率分别为44.7%、42%、20.7%和4.3%, W 147水淹后分别为76.3%、23%、15%和26.3%, 高于其他物种。(3) 水淹后种子萌发时间格局也受到影响, 大部分种子起始萌发时间推迟、萌发速度变慢。鱧肠、黄花蒿、婆婆针和旱稗的种子对三峡库区消涨带的水淹胁迫具有一定的适应能力, 可根据它们对水淹条件适应能力的差异在消涨带不同海拔高度进行植被恢复。

Effects of submergence on seed germination of nine annual plant species in the Three Gorges Reservoir region and their implication to vegetation restoration

The water-level-fluctuation zone of the Three Gorges Reservoir was assumed to be completely formed in 2009 and the water level would range from 145 m in flood season (summer) to 175 m during non-flood season (winter). This hydrologic regime is the opposite of the Yangtze River's natural regime before the Three Gorges Dam construction when the peak flows occurred in summer and low flows occurred in winter. The reversal of flooding time, prolonged flooding duration will dramatically alter environmental conditions in the riparian zone. The fragility of the water-level-fluctuation zone has been widely recognized by Chinese scientific community and governments. It is common view that vegetation should give a priority for ecological restoration in the water-level fluctuation zone. Considering the special hydrological environment, annual plant species was assumed to be dominant component of the vegetation communities for their ability to fulfill their life history during the drawdown period. In order to select suitable annual plant resources for vegetation restoration, we examined the germination characteristics of fresh, cold stored and submerged (W 165-8 m, 121 d; W 155-18 m, 230 d; W 147-26 m, 271 d) seeds of nine annual plant species(Eclipta prostrate, Bidens pilosa, Artemisia annua, Aeschynomene indica, Digitaria sanguinalis, Echinochloa hispidula, Conyza canadensis, Bidens bipinnata, Setaria glauca), which growing in the Three Gorges Reservoir region. The submerged seeds were placed in the water-level-fluctuation zone of the Three Gorges Reservoir. The results indicated that effects of submergence in relation to fresh seeds on the germination percentage varied with the submergence conditions. In W 165 submergence treatment, germination percentages of seven species decreased significantly, and tow, E. hispidula and B. bipinnata had opposite trends. Germination percentages of six species decreased significantly, and three species germinated with low germination percentages 11.0%, 7.3% and 2.7% respectively in W 155. In W 147, germination percentages of E. hispidula and B. bipinnata also increased significantly, while germination percentages of E. prostrate showed no difference, and other species decreased significantly. No significant submergence effect was detected for D. sanguinalis, C. Canadensis and S. glauca, because they had very low germination percentages in all treatments. Seeds of E. prostrata, A. annua, B. bipinnata and E. hispidula demonstrated better tolerance to water submergence. In W 165 submergence treatment, their germination percentages were 44.7%, 42%, 20.7% and 4.3%, respectively. In W 147, germination percentages were 76.3%, 23%, 15% and 26.3%, respectively, and they were higher than other species. The temporal patterns of seed germination were also significantly influenced by submergence, manifesting in two ways, days to initial germination increased and the germination speed decreased for most of the species. It can be concluded that the seeds of E. prostrata, A. annua, B. bipinnata and E. hispidula are submergence-tolerant, and the plants are able to accomplish their life history during the drawdown period. The result of this experiment suggests great potential of annual plant species in vegetation restoration of water-level-fluctuation zone in the Three Gorges Reservoir. And we should apply them according their different biological characters. E. prostrate and E. hispidula can be used at the lower elevations of water-level-fluctuation zone while A. annua and B. bipinnata should be planted at the upper elevations.