Community traits affect plant–plant interactions across climatic gradients

Plant abundances and demography often vary along gradients of environmental stress, and neighboring plants can amplify or diminish such variation. We asked to what degree the effects of neighboring plants on a focal species can be explained by the traits and abundances of species in the surrounding community. We studied a common understory herb, Trientalis latifolia, across climatic gradients created by topography in the Siskiyou Mountains, southwestern Oregon. We compared Trientalis fitness along these gradients with and without neighbor removal, and asked whether the effects of neighboring plants could be predicted by their community-weighted trait values and abundances. Environmental conditions alone did not explain whether neighbors had competitive or facilitative effects on Trientalis. However, the environment interacted with neighbor traits and biomass to influence neighbor effects: at cool, higher elevations, high neighbor biomass was associated with stronger facilitative effects, while at warm, lower elevations, high neighbor dissimilarity from Trientalis was associated with stronger competitive effects. We suggest that covariation and interactions among environmental and community characteristics are key to understanding species performance along climatic gradients.

植物的多度与种群动态常随环境胁迫梯度发生变化，而邻体植物可放大或削弱此类变异。本研究旨在探究：邻体植物对目标物种的作用，在多大程度上可由周边群落中各物种的功能性状与多度加以解释。本研究以美国俄勒冈州西南部锡斯基尤山脉中由地形塑造的气候梯度为研究场景，针对常见林下草本植物宽叶七瓣莲(Trientalis latifolia)展开调查。我们对比了去除邻体与保留邻体两种情境下，宽叶七瓣莲在上述气候梯度中的适合度，并探究邻体植物的作用是否可通过其群落加权性状值与多度进行预测。仅靠环境条件，无法解释邻体植物对宽叶七瓣莲产生的是竞争还是促进作用。但环境条件会与邻体性状及生物量产生交互作用，进而影响邻体的作用效果：在凉爽高海拔区域，邻体高生物量与更强的促进作用呈正相关；而在温暖低海拔区域，邻体与宽叶七瓣莲的性状差异度越高，其竞争作用越强。本研究认为，环境与群落特征间的协变关系及交互作用，是理解物种沿气候梯度生长表现的关键所在。