Vallisneria americana is a broadly distributed North American macrophyte with growth characteristics that vary across regions. While its reproductive traits may also differ with geography, most investigations have occurred in its northern extent, resulting in uncertainty regarding life history and germination strategies in sub-tropical populations. We conducted field monitoring and greenhouse and growth chamber experiments to investigate sub-tropical V. americana seed production, seed banking, and germination cues in central Florida, USA. We observed seed production nearly year-round, which produced a persistent seed bank (where present), with variable, but sometimes high densities (0–6209 seeds/m²). Unlike northern populations that germinate readily, these sub-tropical seeds were dormant, as germination was minimal across temperatures 20–30ºC in light or dark conditions. We found germination was not initiated by individual factors including temperature shifts, warm or cold stratification, high or low dissolved oxygen, or chemicals common in submerged sediments (ethylene or ethanol). However, germination did occur when organic material (sediments and/or vegetative extracts) was present combined with light or following scarification; and germination was enhanced by ethanol and cold-stratification. We also found that germination occurs in organic sediments exposed to high-oxygen conditions but is further improved in low-oxygen organic sediments, possibly mediated by the release of ethanol during oxygen reduction. This enhanced germination in light, decaying organic material, low-oxygen conditions, and ethanol suggests a germination strategy focused on exploiting openings in existing vegetation following disturbance. Without tubers that are present in northern ecotypes, sub-tropical V. americana may rely on seed germination for population maintenance.

美洲苦草是一种广泛分布的北美大型植物，其生长特征因地区而异。虽然其繁殖特征也可能因地理位置而异，但大多数调查都发生在其北部地区，导致亚热带种群的生活史和发芽策略存在不确定性。我们进行了现场监测以及温室和生长室实验，以调查美国佛罗里达州中部的亚热带美洲葡萄种子生产、种子库和发芽线索。我们几乎全年观察种子生产，这产生了持久的种子库（如果存在），其密度可变，但有时很高（0-6209 粒种子/m ²）。与容易发芽的北方种群不同，这些亚热带种子处于休眠状态，因为在光照或黑暗条件下，在 20–30°C 的温度下发芽率最低。我们发现发芽并不是由个别因素引发的，包括温度变化、温暖或寒冷的分层、高或低溶解氧或水下沉积物中常见的化学物质（乙烯或乙醇）。然而，当有机物质（沉积物和/或植物提取物）与光结合或松土后，发芽确实发生；乙醇和冷层积可促进发芽。我们还发现，在暴露于高氧条件的有机沉积物中发芽发生，但在低氧有机沉积物中进一步改善，这可能是通过氧还原过程中乙醇的释放介导的。这种在光照、腐烂的有机物质、低氧条件和乙醇中增强的发芽表明，发芽策略的重点是利用现有植被在干扰后的开口。没有北方生态型、亚热带地区存在的块茎美洲五味子可能依靠种子发芽来维持种群。