Seed bank dynamics of an invasive alien species, Helianthus annuus L

Abstract

AimsThe ability to form persistent seed banks is one of the best predictors of species´ potential to establish in new ranges. Wild sunflower is native to North America where the formation of persistent seed banks is promoted by disturbance and it plays a key role on the establishment and persistence of native populations. However, the role of the seed banks on the establishment and persistence of invasive populations has not been studied. Here, we evaluated the role of seed bank and disturbance on the establishment and fitness, and seed persistence in the soil in several sunflower biotypes collected in ruderal (wild H. annuus) and agrestal (natural crop-wild hybrid) habitats of Argentina as well as volunteer populations (progeny of commercial cultivars).MethodsIn a seed-bank experiment, we evaluated emergence, survival to reproduction, survival of emerged seedlings, inflorescences per plant and per plot under disturbed and undisturbed conditions over two years; in a seed-burial experiment, we evaluated seed persistence in the soil over four springs (6, 18, 30 and 42 months).Important FindingsOverall, seedling emergence was early in the growing season (during winter), and it was promoted by disturbance, especially in the first year. Despite this, the number of inflorescences per plot was similar under both conditions, especially in ruderals. In the second year, emergence from the seed bank was much lower, but the survival rate was higher. In the seed-burial experiment, genetic differences were observed but seeds of ruderals and agrestals persisted up to 42 months while seeds of the volunteer did not persist longer than 6 months. The agrestal biotype showed an intermediate behavior between ruderals and volunteers in both experiments. Our findings showed that wild and crop-wild sunflower can form persistent seed banks outside its native range and that disturbance may facilitate its establishment in new areas.

形成持久种子库的能力是预测物种在新区域成功建群的最佳指标之一。野生向日葵(Helianthus annuus L.)原产于北美，干扰促进了其种子库的形成，并对本地种群的建立和延续起着关键作用。然而，种子库在入侵种群的建立和延续中所起的作用尚不清楚。在本研究中，我们评估了种子库和干扰对几种向日葵生物类型(采集于阿根廷荒地生境中的野生向日葵、野生农田野生向日葵与作物向日葵自然杂交种，以及商业品种的后代)的建立和适应性，以及土壤中种子持久性的作用。在种子库试验中，我们评估了上述材料两年在干扰和未干扰条件下的出苗率、成活率到繁殖率、出苗成活率、每株花序数和每块地的花序数；在种子埋藏试验中，我们评估了其种子在四个春季(6个月、18 个月、30个月和42个月)土壤中的持久性。研究结果表明，总体而言，幼苗在生长期(冬季)出苗较早，且受到干扰促进，尤其是第一年。尽管如此，在两种情况下，每块样地的花序数是相近的，尤其是荒地生境中。第二年，种子库出苗率较低，但成活率较高。在种子掩埋实验中，观察到遗传差异，荒地和野生生境中种子持久性达到42个月，而商业品种后代的种子持久性不超过6个月。在这两项实验中，农田野生型和商业向日葵品种后代生物型表现出一种中间行为。结果表明，野生向日葵和作物野生向日葵杂交种均能在其生长范围之外形成持久的种子库，且干扰可能有助于其在新区域的建立。