Germination performance of alien and native species could shape community assembly of temperate grasslands under different temperature scenarios

Rising temperatures due to climate change are expected to interplay with biological invasions, and may enhance the spread and growth of some alien species upon arrival in new areas. To successfully invade, a plant species needs to overcome multiple biological barriers. Among the crucial life stages, seed germination greatly contributes to the final species assembly of a plant community. Several studies have suggested that alien plant success is related to their high seed germination and longevity in the soil. Hence, our aim is to test if the germination potential of alien seeds present in the seed bank will be further enhanced by future warming in temperate dry grasslands, an ecosystem that is among those most prone to biological invasions. We designed a laboratory germination experiment at two temperatures (20 and 28 °C), to simulate an early or late heat wave in the growing season, using seeds from nine common grassland Asteraceae species, including native, archaeophyte and neophyte species. The test was performed on both single and mixed pools of these categories of species, using a full-factorial orthogonal design. The warmer germination temperature promoted neophyte success by increasing germination probability and germination speed, while negatively impacting these parameters in seeds of native species. The co-occurrence of native and archaeophyte seeds at the lower temperature limited the invasiveness of neophytes. These results provide important information on future management actions aimed at containing alien plant invasions, by improving our knowledge on the possible seed-bank response and interaction mechanisms of common species occurring in disturbed natural areas or restored sites.

气候变化引发的气温上升预计将与生物入侵产生交互作用，并可能提升部分外来物种抵达新区域后的扩散与生长能力。要成功实现入侵，植物物种需突破多重生物屏障。在其关键生活史阶段中，种子萌发对植物群落的最终物种组成构建具有重要贡献。已有多项研究证实，外来植物的入侵成效与其高种子萌发能力及土壤种子存活寿命密切相关。据此，本研究旨在验证：在温带干旱草原这一极易发生生物入侵的生态系统中，未来气候变暖是否会进一步提升土壤种子库中外来种子的萌发潜力。本研究设置了20℃与28℃两个温度梯度的室内萌发实验，以模拟生长季早期或晚期的热浪事件；实验材料取自9种常见草原菊科（Asteraceae）物种，涵盖本土种、古归化种与新归化种三类。实验采用完全因子正交设计，分别针对单类物种池与多类物种混合池开展测试。较高的萌发温度可通过提升萌发率与萌发速率，促进新归化种的入侵成效，却对本土物种种子的上述两项参数产生负面影响。在较低温度条件下，本土种与古归化种种子的共存会抑制新归化种的入侵能力。本研究结果深化了我们对受干扰自然区域或修复生境中常见物种的种子库响应及种间互作机制的认知，可为未来防控外来植物入侵的管理措施提供重要参考依据。