Co-occurring invasive plant and propagule pressure accelerate invasion, but only multiple species invasion changes ecosystem multifunctionality

The understanding of the interactions between individual invasive plant species in biological invasion is currently limited. Specifically, the impact of both invasive plant richness (interaction between invasive species) and abundance (propagule pressure) is likely to be crucial in determining invasion outcomes and their potential effects on ecosystem functions and multifunctionality. Here, we conducted a mesocosm experiment to assess the effects of different levels of invasive plant richness and abundance on invasion success, community properties, ecosystem functions, and multifunctionality. We show that both invasive plant richness and abundance promoted invasion success, primarily due to the allelopathic effects on native plants. We also observed invasive plant richness had different effects on ecosystem functions, and an initial increase followed by a subsequent decrease in ecosystem multifunctionality as invasive plant richness increased, with no significant impact from invasive plant abundance. This suggests that the interaction between invasive plants plays a more important role in the impacts on ecosystem functions and multifunctionality than propagule pressure. Furthermore, plant invasion indirectly affected multifunctionality by impacting species diversity indices and environmental factors. These results highlight the potential for aggravated biological invasion and intensified ecosystem damage in the future as multiple invasive species co-invade.

目前学界对生物入侵过程中不同入侵植物物种间的相互作用机制认知仍较为有限。具体而言，入侵植物丰富度（即入侵物种间的相互作用）与入侵植物多度（繁殖体压力(propagule pressure)）对入侵结局及其对生态系统功能与生态系统多功能性的潜在影响，均为决定入侵结果的关键因素。本研究通过开展中型实验生态系统(mesocosm)实验，评估了不同梯度的入侵植物丰富度与多度对入侵成功性、群落特征、生态系统功能及生态系统多功能性的影响。研究结果显示，入侵植物丰富度与多度均可提升入侵成功性，其核心驱动机制为对本土植物发挥化感作用。此外还发现，入侵植物丰富度对生态系统功能存在差异化影响；随着入侵植物丰富度升高，生态系统多功能性呈现先升后降的变化趋势，而入侵植物多度未对其产生显著影响。这表明相较于繁殖体压力，入侵植物间的相互作用对生态系统功能与多功能性的影响更为关键。进一步分析显示，植物入侵可通过影响物种多样性指数与环境因子，间接作用于生态系统多功能性。本研究结果凸显了未来多入侵物种共同入侵时，生物入侵态势或将加剧、生态系统受损程度或将加重的潜在风险。