Data from: Phenotypic effects of the nurse Thylacospermum caespitosum on dependent plant species along regional climate stress gradients

Contrasting phenotypes of alpine cushion species have been recurrently described in several mountain ranges along small-scale topography gradients, with tight competitive phenotypes in stressful convex topography and loose facilitative phenotypes in sheltered concave topography. The consistency of phenotypic effects along large-scale climate stress gradients have been proposed as a test of the likely genetic bases of the differences observed at small-scale. Inversely, plastic phenotypic effects are more likely to vanish at some points along climate stress gradients. We tested this hypothesis for two phenotypes of the alpine cushion species Thylacospermum caespitosum at four points along regional gradients of cold and drought stress in northwest China. We measured the traits of the two cushion phenotypes and quantified their associated plant communities and environmental variables along the regional temperature and aridity gradients. Cushion height, convexity and stem density overall showed significant effect of phenotypes. Difference in tightness of cushions between phenotypes was consistent across climate conditions, whereas differences in cushion convexity and height between phenotypes increased with increasing cold stress. Phenotypic effects on species richness and abundance were consistent along both climate gradients but not effects on species composition, while there were no phenotypic effects on environmental variables. Additionally, RII (relative interaction index) curves were linear along the drought gradient but unimodal along the temperature gradient, likely due to the occurrence of contrasting species pools at the different sites. We conclude that the consistency of phenotypic effects of T. caespitosum was high for species richness and abundance and mainly explained by differences in interference mediated by likely heritable differences in cushion tightness. Additionally, our study shows that the shapes of the relationship between plant responses to neighbours and environmental stresses are not necessarily driven by niche-based deterministic factors.

高山垫状植物的对立表型已在多条山脉的小尺度地形梯度中被反复报道：在胁迫性凸地形中呈现紧凑的竞争型表型，而在遮蔽性凹地形中则表现为松散的互利型表型。沿大尺度气候胁迫梯度的表型效应一致性，被提议作为检验小尺度观测到的表型差异潜在遗传基础的研究路径。与之相反，可塑性表型效应更有可能在气候胁迫梯度的某些位点消失。我们针对中国西北部沿寒冷与干旱胁迫区域梯度分布的4个样点，对高山垫状植物囊种草（Thylacospermum caespitosum）的两种表型开展了该假说的验证实验。沿区域温度与干旱梯度，我们测定了两种垫状表型的性状，并量化了其关联的植物群落与环境变量。总体而言，垫状体高度、凸度与茎密度均表现出显著的表型效应。两种表型的垫状体紧密度差异在各类气候条件下均保持稳定，而二者在垫状体凸度与高度上的差异则随寒冷胁迫加剧而增大。表型对物种丰富度与多度的效应在两条气候梯度上均保持一致，但对物种组成的效应则未表现出这种一致性；同时，表型对环境变量并无显著效应。此外，相对互作指数（Relative Interaction Index, RII）的曲线在干旱梯度上呈线性，而在温度梯度上呈单峰模式，这可能缘于不同样点的物种库存在显著差异。我们的研究结论表明，囊种草（T. caespitosum）的表型效应对物种丰富度与多度的一致性较高，这主要可通过垫状体紧密度的潜在可遗传差异所介导的种间干扰差异来解释。此外，本研究还揭示，植物对邻体的响应与环境胁迫之间的关系模式，未必由基于生态位的确定性因素所驱动。