Data from: The balance of canopy and soil effects determines intraspecific differences in foundation species’ effects on associated plants

1. The impact of plant-plant interactions on species diversity patterns has been broadly addressed in stressful environments, such as alpine ecosystems, where foundation species promote species richness by creating habitat for other species. However, foundation species with contrasting phenotypes might modify the microhabitat differently, which would alter the subordinate community composition, and coincide with distinct feedback effects of those subordinate species on the foundation species. However, the precise interaction mechanisms that facilitate species are not fully understood, especially the relative contribution of above- and below-ground compartments of foundation species to subordinate species and the potential feedbacks they receive. 2. We explored whether two contrasted canopy phenotypes (tight and loose) of the shrub Cytisus galianoi differed in their effects on the microhabitat and on subordinate plant community composition in a dry subalpine system. We also experimentally distinguished the relative contribution of above- (canopy) and below-ground (soil) effects of C. galianoi on the most frequent subordinate species, Festuca indigesta, as well as the reciprocal effects of F. indigesta on C. galianoi. 3. We performed observational and manipulative experiments to assess the influence of phenotypic differences of the shrub on understory microhabitat and subordinate plant community composition. Reciprocal effects were assessed by removing either F. indigesta from the understory of the two shrub phenotypes or the C. galianoi canopy from the immediate vicinity of F. indigesta. 4. The two C. galianoi phenotypes differed in mean values of functional traits (like stem density or plant height), modified their understory microhabitats differently, and hosted distinct subordinate communities. Loose phenotypes had more positive effects on community composition and diversity than tight phenotypes. Additionally, tight phenotypes simultaneously showed both more positive aboveground and more negative belowground effects on F. indigesta than loose phenotypes. There were no significant feedback effects of F. indigesta on C. galianoi. 5. The two phenotypes of the foundation species C. galianoi showed contrasting effects on the subordinate plant community: compared to the tight phenotype, the loose phenotype had higher associated species diversity and reduced reciprocal interaction intensities above- and below-ground with the subordinate species F. indigesta. This highlights the impact of phenotypic variation for plant interactions and community-level diversity.1. 植物间相互作用对物种多样性格局的影响，在胁迫环境中已得到广泛研究，例如高山生态系统（alpine ecosystems），其中基础物种（foundation species）通过为其他物种创造栖息生境来提升物种丰富度。然而，表型迥异的基础物种可能会以不同方式改造微生境（microhabitat），进而改变从属群落（subordinate community）组成，并与这些从属物种对基础物种的独特反馈效应相契合。但目前学界尚未完全阐明促进物种共存的精准互作机制，尤其是基础物种的地上与地下组分（above- and below-ground compartments）对从属物种的相对贡献，以及二者所接收的潜在反馈效应。 2. 本研究探究了干旱亚高山生态系统中，两种冠层表型（紧凑型与松散型）的灌木*Cytisus galianoi*对微生境及从属植物群落组成的影响是否存在差异。我们还通过实验区分了该灌木的地上（冠层）与地下（土壤）效应对最常见的从属物种羊茅属*Festuca indigesta*的相对贡献，以及该羊茅物种对该灌木的反向效应。 3. 本研究开展了观测性与控制性实验，以评估该灌木的表型差异对林下微生境及从属植物群落组成的影响。通过两种方式评估反向互作效应：一是从两种灌木表型的林下移除该羊茅物种，二是从该羊茅物种的紧邻生境移除该灌木的冠层。 4. 两种该灌木表型在功能性状（如茎密度、株高）的均值上存在差异，且对林下微生境的改造方式各不相同，其所承载的从属群落也存在显著区别。相较于紧凑型表型，松散型表型对群落组成与多样性的促进效应更强。此外，与松散型表型相比，紧凑型表型对该羊茅物种同时表现出更强的正向地上效应与更强的负向地下效应。而该羊茅物种对该灌木未表现出显著的反馈效应。 5. 基础物种*Cytisus galianoi*的两种表型对从属植物群落表现出截然相反的影响：与紧凑型表型相比，松散型表型所伴生的物种多样性更高，且与从属物种*Festuca indigesta*之间的地上、地下互惠交互强度更低。这一结果凸显了表型变异对植物互作及群落水平多样性的重要影响。