Data from: Pescador et al. Alone or accompanied? Interactions during early-life stages of Mediterranean shrubs depend on environmental conditions and neighbours’ phenotypic and phylogenetic differences

· Background and Aims Plant-plant interactions are crucial in Mediterranean ecosystems for coping with drought conditions, but it remains unclear how these interactions are modulated during plant establishment. This study examined how drought influences plant performance during early life stages and whether interactions depend on functional similarity and phylogenetic distance to the neighbourhood.· Methods We conducted a common garden experiment using seeds of 20 perennial species from a Mediterranean shrubland (central Spain). Four of these perennials (focal species) grew during their early life stage either alone, with conspecifics or with individuals of the remaining perennials, in both a control and drought treatments. Four functional traits were measured in all focal species individuals to estimate interaction patterns through the Relative Intensity Index (RII). We then tested whether RII values were related to the phylogenetic or functional similarity between species.· Key Results Drought and neighbour presence induced negative effects on plant performance, prevailing competition during early life stages. Both RIIbiomass and RIIFv/Fm were significantly more negative under drought conditions, suggesting that water scarcity results in individuals with lower biomass and reduced Fv/Fm, an indicator of photosynthetic efficiency, when grown with neighbours. The relationship between interaction patterns and phylogenetic or functional relatedness was species-specific, with some focal species competing more intensely when they grew with similar species (according to the limiting similarity hypothesis), and other species showing the opposite pattern (consistent with the competition-trait hierarchy hypothesis).· Conclusions These results challenge the idea that lower phylogenetic or functional similarity always reduces competition, highlighting the need for future research to consider the complexity of plant interactions between neighbours and across ontogeny.

· 研究背景与研究目的
植物间相互作用对于地中海生态系统应对干旱环境至关重要，但目前对植物定植阶段这些相互作用的调控机制仍不明确。本研究探讨了干旱如何影响植物早期生活史阶段的生长表现，以及这些相互作用是否取决于目标物种与邻株的功能相似性和系统发育距离。
· 研究方法
本研究以采自西班牙中部地中海灌丛的20种多年生植物种子为材料开展同质园实验。其中4种多年生植物（目标物种）在早期生活史阶段，分别以单株种植、与同种个体伴生或与其余多年生植物伴生的方式种植，并设置对照组与干旱处理组。我们测定了所有目标物种个体的4项功能性状，基于相对强度指数（Relative Intensity Index，RII）量化植物间相互作用模式。随后我们检验了RII值是否与物种间的系统发育或功能相似性相关。
· 主要研究结果
干旱处理与邻株伴生均会对植物生长表现产生负面影响，在早期生活史阶段竞争作用占据主导地位。在干旱条件下，生物量相对强度指数（RIIbiomass）与光合效率指标Fv/Fm相对强度指数（RIIFv/Fm）均显著更负，表明水分匮乏会导致邻株伴生的个体生物量更低、光合效率指标Fv/Fm表现更差。植物间相互作用模式与系统发育或功能亲缘关系的关联具有物种特异性：部分目标物种与功能相似的类群伴生时竞争作用更强（符合限制相似性假说），而另一些物种则呈现相反的模式（与竞争-性状层级假说一致）。
· 研究结论
本研究结果挑战了“更低的系统发育或功能相似性总能降低竞争作用”这一观点，凸显了未来研究需考虑邻株间以及不同发育阶段植物相互作用的复杂性的必要性。