恶性入侵杂草豚草的种子萌发母体效应及生态适应性

Seed germination pattern determines the seed bank persistence and the invasive possibility of alien plant population. Researches demonstrate that seed innate secondary domancy occurs in Ambrosia artemisiifolia, an annual invasive plant. When seeds mature in autumn, they are innately dormant (primary dormancy). Seeds in primary dormancy require moist chilling (stratification) to come out of dormancy, and in nature this occurs during winter. In the natural habitat seeds of A. artemisiifolia germinate only in spring, and the peak of germination occurs in early to mid-spring. Nondormant seeds that fail to germinate in spring enter secondary dormancy. Seeds in secondary dormancy require stratification to come out of dormancy, and it has been postulated that buried seeds can go into and out of secondary dormancy many times. However, our results show that autumn germinated seedlings occurs in investigated populations. Obviously, secondary domancy can not explain this phenomenon, and less is known about the adaptive significance of autumn germinated seedlings in this invasive species. Therefore, further study is needed to explore seed germination mechanisms and its ecological adaptability.. Maternal phenotypic characters and the local environment of mather plant during seed maturation affect seed germination and offspring fitness. A. artemisiifolia is plastic to environmental conditions, resulting in many ecotypes in natural populations. Environmental factors and seasonal variations may induce the occurrence of maternal effects on seed germination. However, in previous studies, seed maternal effects on germination were ignored in A. artemisiifolia. To explore maternal effects on seasonal seed germination and ecological adaptability in A. artemisiifolia, we will integrate the methods with morphology, phenology, population ecology and reproductive biology. Population investigation, manipulated experiments and laboratory experiments will be conducted; maternal effects on seed germination, plant growth and reproductive traits and life history traits will be examined. This item will be significant in discussing seed maternal effects on population expandation and succession in an invasive habitat in A. artemisiifolia..

外来入侵植物种子的萌发格局决定种子库持久储备能力及建群的成功率。一年生外来恶性入侵杂草豚草自然种群中种子要经历冬季低温破除休眠，春季集中萌发，春末夏初未萌发的种子再次休眠，以此过程循环，使豚草种子寿命可长达数十年。我们的研究表明豚草种群存在秋萌现象，二次休眠机制已不能解释这一现象；且秋萌现象的生态适应意义也不清楚。母体影响生活史早期阶段的种子萌发及幼苗建成。基于豚草种子季节性萌发特征及母体效应的研究空白，采用实验生物学及野外生态学的方法，综合运用植物形态学、物候学、生态学、生殖生物学等的研究技术，从母体效应着手研究母体表型及种子成熟期的环境对种子萌发的影响，植株季节性萌发引发的母体效应，豚草种子季节性萌发的机制；从植株生长、繁殖策略、生活史特征及后代适合度方面着手研究豚草种子季节性萌发的生态适应性；以期揭示豚草入侵扩张与蔓延的种子母体效应生态适应机制。

种子的萌发格局是展现外来植物种群入侵性的重要方面。母体特征对生活史早期种子萌发及幼苗建成阶段具有重要意义。农业恶性外来入侵杂草豚草种子的二次休眠机制被认为是该种群种子库维持稳定持久的重要原因，但是二次休眠机制不能解释豚草种群存在的秋季萌发现象。基于豚草种子季节性萌发特征及母体效应的研究空白，本项目突破以往二次休眠机制的局限，从豚草种子季节性萌发，尤其秋季萌发的母体效应入手，通过可塑性很强的豚草的亲子代间适应性可塑性的关联性，阐释豚草种子库的长期维持及种群成功建群的生态学过程与机制。. 本项目主要研究内容包含三部分：萌发时间与生活史策略；种子的母体表型效应；种子的母体环境效应。主要的实验结果表明延迟萌发的植株形态变化明显，植株个体相对矮小，枝条数量与长度，花序数量，果实数量均显著减少；植株生长期缩短，发育节律变快。尽管地上部分生物量减小，但用于繁殖部分的生物量分配比率显著增大，性分配比率减小。高密度下，豚草植株显著增高，植株花序数量减少，果实数量显著降低。植株的生长期长度及生长发育节律变化不显著。地上部分生物量减小，茎在地上部分所占比率增大，繁殖分配比率减小，性分配比率减小。植株的萌发时间与密度环境均显著的影响后代种子萌发。. 豚草生活史性状积极地或消极地响应萌发时间的延后及种内竞争，在植株性状间显现出的权衡关系以及越代效应，表明了豚草响应环境变化而进行的适应性调节。本研究有助于我们理解和认识豚草生态适应的过程和机制。