The ‘stress-gradient hypothesis’ predicts increasing facilitative interactions with increasing environmental stress, but it remains unclear if the prevailing interaction (i.e. facilitative or competitive) of dominant plant species on subordinate plant species occurring in harsh environments is dependent on the plant functional type. In addition, most plant-species removal experiments in grasslands are short-term (1-2 years), which may imprecisely reflect transient effects arising from methodological limitations. We conducted a dominant species removal experiment in a subalpine ecosystem, containing a mosaic of grass-dominated and shrub-dominated community patches, both of which are common in the subalpine zone of the Qinghai-Tibetan Plateau. We examined the direction and magnitude of the effects of three co-dominant grass and a dominant shrub species on subordinate species richness and biomass over a 6-year period. Removal of the dominant grass species alleviated their competitive pressure on subdominant grasses, which resulted in similar total and grass biomass detected in the final year of the study. By contrast, shrub removal showed no effects on its subordinate species biomass. Furthermore, neither the removal of the dominant shrubs nor the grasses altered their respective subordinate species richness. Thus, in subalpine ecosystems that experience harsh environmental conditions, our results showed that the direction of interactive effects of dominant plant species on subordinate species may be dependent on the plant functional type and are not necessarily facilitative. Furthermore, we showed that longer-term plant-removal experiment observations may be required to better determine the effects of species removal for subalpine and montane ecosystem(s).

“胁迫梯度假说”预测随着环境压力的增加，促进的相互作用将增加，但是尚不清楚在恶劣环境下发生的优势植物物种与次要植物物种之间的主要相互作用（即促进或竞争）是否取决于植物功能类型。此外，草原上大多数植物物种清除实验都是短期的（1-2年），这可能无法准确反映出方法学局限性带来的短暂影响。我们在亚高山生态系统中进行了优势种清除实验，其中包含由草为主和灌木为主的群落斑块，这两种斑块在青藏高原的亚高山地带都很常见。我们研究了6年期间三种共生草和优势灌木物种对次生物种丰富度和生物量的影响的方向和程度。去除优势草种可减轻它们对优势草的竞争压力，从而在研究的最后一年中检测到类似的总草木量。相比之下，灌木清除对其下属生物量没有影响。此外，去除优势灌木和草都不会改变其各自的从属物种丰富度。因此，在经历恶劣环境条件的亚高山生态系统中，我们的结果表明，优势植物物种对次要物种的相互作用的方向可能取决于植物的功能类型，并不一定具有促进作用。