意大利苍耳二形性种子萌发、植株生长差异及生态适应性

Dimorphic seed germination,plant growth difference,and ecological adaptability of Xanthium italicum

意大利苍耳(Xanthium italicum)是一种具有二形性种子的一年生菊科植物,每个头状花序仅产生1粒上位种子和1粒下位种子。意大利苍耳种子产量高,对环境的适应能力强,能给农作物和生态环境造成严重危害。对意大利苍耳的种子萌发和植株生长特性进行了观测研究,探讨了其生态适应性。结果表明:(1)下位种子从播种到50%萌发需要13～15d,比上位种子早5～7d;(2)下位植株主茎第1～7片叶的发育中期单位时间内的叶面积增量、同期株高显著大于上位植株;然而上位植株主茎第9～13片叶的发育早、中期单位时间内的叶面积增量反而大于下位植株;上、下位植株主茎上第8、14片叶和第15片叶的各阶段单位时间内的叶面积增量没有差异;(3)下位植株的一级分枝数和二级分枝数显著多于上位植株。推断下位种子较上位种子具有更强的生存竞争能力,下位种子对意大利苍耳种群的延续、增长和扩散贡献更大;同时上位种子为种群的稳定延续提供了保障,这种二形性种子的形成是意大利苍耳的一种有效的生态对策。

Xanthium italicum（Asteraceae） is an annual species bearing dimorphic seeds.Each of its capitulum produces only one upper seed and one lower seed.It is productive,adaptable,and harmful to crops and environment.For a better understanding of X.italicum′s ecological adaptation,we studied its seed germination,its plant growth characteristics,and its ecological adaptability.The results showed that：（1） Lower seeds needed 13 to 15 days to reach a 50% germination,which was 5 to 7 days earlier than that of upper seeds.（2） In creasing amounts of leaf area at the interim developmental stage of the 1st to 7th leaves on the main stems of the plants of the lower seeds were significantly greater than that of the plants of the upper seeds.The plants of the lower seeds were notably higher than the plants of the upper seeds during the same period.On the contrary,increasing amounts of leaf area at the early or interim developmental stages of the 9th to 13th leaves on the main stems of the plants of the upper seeds were significantly greater than that of the plants of the lower seeds.No differences appeared during the developmental process of the 8th,14th,and 15th leaves on the main stems between the two kinds of plants.（3） The number of primary branches and secondary branches produced by the plants of the lower seeds were significantly larger than those of the plants of the upper seeds,respectively.From this we concluded that the lower seeds have stronger abilities in survival and competition and contribute much more to the persistence,growth,and extension of the population than the upper seeds,that the upper seeds play an important role in keeping a stable population,and that to bear dimorphic seeds is an effective adaptation strategy for X.italicum.