不同生境的植物有不同的生活史对策。该文对分布于河西走廓的42种常见中生植物和22种常见旱生植物种子的萌发特性以及种子大小对萌发能力的影响进行了比较。结果显示,64种植物中最终萌发率超过90%的有9种: 虎尾草(Chloris virgata)、蒲公英(Taraxacum mongolicum)、腺独行菜(Lepidium apetalum)、膜果麻黄(Ephedra przewalskii)、沼生蔊菜(Rorippa islandica)、白草(Pennisetum centrasiaticum)、霸王(Zygophyllum xanthoxylon)、反枝苋(Amaranthus retroflexus)和黑果枸杞(Lycium ruthenicum),占14.06%,其中黑果枸杞、腺独行菜、膜果麻黄、虎尾草的萌发在10 d内完成; 萌发率达到80%~90%的有5种: 毛果群心菜(Cardaria pubescens)、窄叶小苦荬(Ixeridium gramineum)、牛蒡(Arctium lappa)、鞑靼滨藜(Atriplex tatarica)和苣荬菜(Sonchus brachyotus)占7.8%; 萌发率达到60%~80%的有16种,占25%;萌发率在20%~60%的有17种,占26.56%; 萌发率不足20%的有17种: 柠条锦鸡儿(Caragana korshinskii)、野苜蓿(Medicago falcata)、扁蓄(Polygonum aviculare)、苦参(Sophora flavescens)、河西沙拐枣(Calligonum potanini)、白刺(Nitraria tangutorum)、甘草(Glycyrrhiza uralensis)、苦豆子(Sophora alopecuroides)、骆驼蓬(Peganum harmala)、画眉草(Eragrostis pilosa)、多裂骆驼蓬(Peganum multisectum)、老瓜头(Cynanchum komaroviil )、骆驼蒿(Peganum nigellastrum)、田旋花(Convolvulus arvensis)、酸模叶蓼(Polygonum lapathifolium)、卷茎蓼(Polygonum convolvulus)、蝎虎驼蹄瓣(Zygophyllum mucronatum),占25.56%。有26种植物的萌发持续在30 d以上,15种植物在15 d内完成萌发,有31种植物在1~3 d内开始萌发,4种植物在10 d以后才开始萌发。主成分分析和聚类分析显示,中、旱生植物的萌发主要有爆发型、过渡型、缓萌型和低萌型,以过渡型和缓萌型为主;中生植物中萌发率不足20%的有6种,占14.28%, 旱生植物中萌发率不足20%的有11 种,占50%,显示了较多的旱生植物有延迟萌发的行为,这种萌发的延迟及萌发时间的异质性可使物种在不可预测、高死亡风险的环境中仍能确保种的延续。中生植物的种子大小对萌发能力有显著的影响,小种子的物种有较高的萌发率和较快的萌发速率,并且完成萌发所需要的时间较短,而旱生植物的种子萌发不受种子大小的影响。以上结果说明中生植物和旱生植物长期适应于不同的湿、旱生环境,在不同的选择压力下,生活史对策也出现了较明显的差异。

Aims Seed germination and seed size are crucial plant life history traits related to seedling establishment, survival, competition and fitness. Study of germination ecology of native species not only increases understanding of seed traits, reproductive strategy and physiological adaptation, but also can be applied in ecological restoration. Mesad and siccocolous species with different water requirements may have different life-history strategies to respond to different selective pressures. Our main purposes were to determine: 1) differences in germination characteristics between mesad and siccocolous species in the arid and semiarid zone and 2) relationship of germination to seed size.

Methods Seeds of 42 mesad and 22 siccocolous species from the Hexi Corridor of Northwest China were air-dried, cleaned and stored at room temperature about 3-4 months and then stored at 2-4 ℃ for 40 d. Germination was determined under an alternating temperature regime (25 ℃/5 ℃; 12 h light/dark). Four main germination indices were recorded: germination percentage, germination rate, days to first germination and germination period. PCA was used to survey the germination patterns of the 64 species, and Pearson Correlation Analysis was used to determine the relationship of seed size and germination.

Important findings There are four main germination patterns: rapid, intermediate, slow and low germination. Low germination percentages (≤20%) were found in 14.28% mesad and 50% siccocolous. There are significant differences in seed size between mesad and siccocolous (p=0.003). There also is a significant negative correlation between germination and seed size in mesad, with smaller-seeded species having higher germination percentages (r=-0.467^**, p=0.002) than larger-seeded ones, but not in siccocolous (p>0.05). Findings indicate that mesad and siccocolous species under different water conditions are subjected to different selective pressures and have evolved different life-history strategies.