摘要:豚草（Ambrosia artemisiifolia Linn.）和三裂叶豚草（A.trifida Linn.）是我国恶性入侵物种，分布常呈高密度单一种群，且结实量庞大。探讨二者不同植株部位种子萌发（休眠）与扩散特点，对了解二者入侵机制具有重要意义。以新疆伊犁新源县发生的豚草和三裂叶豚草为材料，在种子成熟期，根据植株高度、枝条长度，按比例从上到下分为9个部位，对不同植株部位种子的形态特征、数量和萌发特性进行比较，分析这两种植物不同植株部位种子萌发与扩散的共性和差异性，研究二者种群密度调节和入侵的关系。结果表明：1）两个物种内不同植株部位间种子的长、宽、百粒重无显著差异，但三裂叶豚草种子的长度和宽度分别是豚草的2-3倍，百粒重高7倍。结合两个物种在伊犁地区分布差异，认为种子大小是两个物种分布区域性差异的原因之一。2）豚草和三裂叶豚草植株外部的上顶、中顶、上中部位种子数占植株总种子数量的50%，中中、下顶占比约23%，而下部的上基、中基、下中、下基的种子数占比约27%，表明当年生产的种子有近73%的比例具有远距离扩散的潜力。3）豚草和三裂叶豚草不同植株部位种子的萌发率具有上端 > 中端 > 下端的趋势；初始萌发时间为下端 > 中端 > 上端；萌发持续时间为上端 > 中端 > 下端。这种萌发方式避免了同一生长季大批种子同时萌发有可能导致高密度死亡的风险。基于上述研究分析，认为豚草和三裂叶豚草不同植株部位种子具有不同的适应功能。其中，上部所产生的种子具较强的扩散能力和低休眠性，有利于两物种快速占据新生境并扩大种群；而中、下部位的种子在母株周围就近扩散，翌年萌发率低，缓解了种群竞争。豚草和三裂叶豚草不同植株部位生产的种子特性和萌发差异是两个物种进行种群密度调节和扩散入侵的重要原因。



Abstract:Ambrosia artemisiifolia Linn. and A. trifida Linn. are exotic invasive plant species in China. They are often distributed in populations at high density, and they yield abundant fruits. It is important to study the characteristics of germination (dormancy) and diffusion (distribution) of seeds of both species produced on different parts of the mother plant to enhance the understanding of the mechanisms of their invasion. In this study, we used A. artemisiifolia and A. trifida plants collected from Xinyuan County, Yili, Xinjiang. Plants were proportionally divided into nine positions from top to bottom according to plant height and branch length. Morphological characteristics, quantity and germination characteristics of the seeds produced, and diffusion of seeds originating from the nine positions were compared. The relationship between population density regulation and invasion was also studied. The results showed that:1) There was no significant difference in length, width and 100-seed weight of seeds produced at different positions between the two species, but the lengths and widths of the seeds of A. trifida were 2-3 times greater than those of A. artemisiifolia. The 100-seed weight of A. trifida was seven times greater than that of A. artemisiifolia. In combination with the different distributions of the two species in Xinyuan, it was considered that seed size is a factor affecting the regional differences in distribution of the two species. 2) The number of seeds produced in positions Up Up (UU), Middle Up (MU) and Up Middle (UM) of A. artemisiifolia and A. trifida was about 50% of the total number of seeds produced by the plant. Seed yield in positions MM and BU was about 23% of the total, while production in the lower positions of UB, MB, BM and BB was about 27%. This meant that 73% of the seeds produced in the year had the potential for long distance diffusion. 3) The germination rates of seeds produced at different plant positions of A. artemisiifolia and A. trifida showed a trend of upper positions > middle positions > lower positions; while the initial germination time was lower positions > middle positions > upper positions; and germination duration followed the trend of upper positions > middle positions > lower positions. This pattern of seed germination avoided the risk of simultaneous germination by large numbers of seeds in the same growing season, which might lead to high mortality at high seeding density. On the basis of the above analysis, it was concluded that the seeds produced at different positions on plants of A. artemisiifolia and A. trifida showed different adaptive functions; seeds from the upper position of plants possess strong diffusivity and low dormancy, which is a beneficial feature, enabling them to occupy new environments rapidly and expand their populations. However, the seeds produced in the middle and lower positions diffuse around the parent plants, and their germination rates were low, which alleviated intraspecific competition. The characteristics and germination differences of seeds produced at different positions of A. artemisiifolia and A. trifida are important factors for regulating population density and invasion patterns of both species.





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