High genotypic diversity and strong spatial structure in populations of Trifolium alpestre with low seed production

The studies on clonal plant populations indicate that the proportion between clonal and sexual reproduction may be highly variable, depending on the biological characteristics of species and the ecological conditions of habitats. We focused on the genotypic diversity of Trifolium alpestre populations in Estonia. We assayed the genetic diversity, spatial genotypic structure and diversity with the use of allozyme markers. Populations revealed high levels of genotypic diversity and showed strong spatial structure of MLGs. The values of genetic diversity were moderately high. Spatially aggregated, identical genotypes spread up to 15 meters along the linear transects and in 4 m2 plots indicate extensive clonal propagation in populations. However, numerous unique and small-sized clones in transects and quadrates reflect significant contribution from the sexual reproduction. The spatially and temporarily stochastic soil disturbances have evidently opened new opportunities for the successful sexual reproduction from the permanent soil seed bank and have thus avoided the losses of genotypic and genetic diversity. The seed production in all populations during the three study years was low, in average up to 1.5-2.4 seeds per shoot. The almost total lack of seed set from all 57 bagged flower heads of genets grown in a common garden indicates that T. alpestre needs pollinators for the seed production.

有关克隆植物种群的研究表明，克隆繁殖与有性繁殖的占比可能存在极高变异性，其变化取决于物种的生物学特性以及栖息地的生态条件。
本研究聚焦于爱沙尼亚境内高山车轴草（Trifolium alpestre）种群的基因型多样性。我们采用同工酶标记（allozyme markers）技术，对其遗传多样性、空间基因型结构及多样性水平展开了测定与分析。种群表现出较高水平的基因型多样性，且多基因座基因型（Multi-Locus Genotypes，MLGs）呈现出显著的空间结构，遗传多样性数值处于中等偏高水平。
沿线性样线分布、空间聚集的相同基因型，以及4平方米样方内的相同基因型，其扩散范围可达15米，这表明种群内存在广泛的克隆繁殖。
然而，样线与样方中大量存在的独特小型克隆株系，反映出有性繁殖对种群做出了显著贡献。
空间与时间上随机发生的土壤干扰，显然为永久土壤种子库（soil seed bank）中成功完成有性繁殖创造了新契机，进而避免了基因型与遗传多样性的流失。
在三年研究周期内，所有种群的种子产量均较低，平均每茎仅结1.5至2.4粒种子。
在同质种植园（common garden）中栽培的57个基株（genet）的套袋头状花序（bagged flower heads）几乎完全无法结实，这表明高山车轴草需要传粉者才能完成种子生产。