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，沿小尺度地形梯度在多个山脉中被反复报道：胁迫性凸地形中呈现紧凑的竞争型表型，而遮蔽性凹地形中则表现为松散的互利型表型。此前有研究提出，沿大尺度气候胁迫梯度的表型效应一致性，可用于检验小尺度观测到的表型差异的潜在遗传基础；反之，表型可塑性效应则可能在气候胁迫梯度的某些位点消失。我们以中国西北寒冷与干旱胁迫区域梯度上的4个采样点为研究对象，针对高山垫状植物囊种草（Thylacospermum caespitosum）的两种表型开展假说验证。我们测定了两种垫状表型的功能性状，并量化了沿区域温度与干旱梯度分布的相关植物群落与环境变量。总体而言，垫状体高度、凸度与茎密度均存在显著的表型效应。两种表型间垫状体紧实度的差异在不同气候条件下保持一致，而二者间垫状体凸度与高度的差异则随寒冷胁迫加剧而增大。表型效应对物种丰富度与多度的影响沿两条气候梯度均保持一致，但对物种组成的影响则未呈现此规律；此外，表型对环境变量无显著影响。此外，相对互作指数（Relative Interaction Index, RII）沿干旱梯度呈线性分布，而沿温度梯度则呈单峰分布，这可能缘于不同采样点间物种库存在差异。综上，囊种草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实度的可遗传差异介导的干涉作用差异来解释。本研究同时表明，植物对邻体的响应与环境胁迫间的关系形态，未必由基于生态位的确定性因素所驱动。