Global change is affecting the distribution and population dynamics of plant species across the planet, leading to trends such as shifts in distribution toward the poles and to higher elevations. Yet, we poorly understand why individual species respond differently to warming and other environmental changes, or how the trait composition of communities responds. Here we ask two questions regarding plant species and community changes over 42 years of global change in a temperate montane forest in Québec, Canada: (1) How did the trait composition, alpha diversity, and beta diversity of understory vascular plant communities change between 1970 and 2010, a period over which the region experienced 1.5°C of warming and changes in nitrogen deposition? (2) Can traits predict shifts in species elevation and abundance over this time period? For 46 understory vascular species, we locally measured six aboveground traits, and for 36 of those (not including shrubs), we also measured five belowground traits. Collectively, they capture leading dimensions of phenotypic variation that are associated with climatic and resource niches. At the community level, the trait composition of high‐elevation plots shifted, primarily for two root traits: specific root length decreased and rooting depth increased. The mean trait values of high‐elevation plots shifted over time toward values initially associated with low‐elevation plots. These changes led to trait homogenization across elevations. The community‐level shifts in traits mirrored the taxonomic shifts reported elsewhere for this site. At the species level, two of the three traits predicting changes in species elevation and abundance were belowground traits (low mycorrhizal fraction and shallow rooting). These findings highlight the importance of root traits, which, along with leaf mass fraction, were associated with shifts in distribution and abundance over four decades. Community‐level trait changes were largely similar across the elevational and temporal gradients. In contrast, traits typically associated with lower elevations at the community level did not predict differences among species in their shift in abundance or distribution, indicating a decoupling between species‐ and community‐level responses. Overall, changes were consistent with some influence of both climate warming and increased nitrogen availability.

中文翻译：

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根系和生物量分配特征预测全球变化四十年中植物物种和群落的变化


全球变化正在影响全球植物物种的分布和种群动态，导致分布向两极和更高海拔地区转移等趋势。然而，我们很少了解为什么单个物种对变暖和其他环境变化的反应不同，或者群落的性状组成如何反应。在这里，我们提出两个关于加拿大魁北克温带山地森林 42 年全球变化中植物物种和群落变化的问题：(1) 1970 年期间林下维管植物群落的性状组成、α 多样性和 β 多样性发生了怎样的变化2010 年，该地区经历了 1.5°C 的变暖和氮沉降的变化？ (2) 性状能否预测这段时间内物种海拔和丰度的变化？对于 46 种林下维管束物种，我们在当地测量了 6 种地上性状，对于其中 36 种（不包括灌木），我们还测量了 5 种地下性状。总的来说，它们捕获了与气候和资源位相关的表型变异的主要维度。在群落水平上，高海拔地块的性状组成发生了变化，主要是两个根性状：比根长度减少和根深增加。高海拔地块的平均性状值随着时间的推移向最初与低海拔地块相关的值转变。这些变化导致了不同海拔地区的性状同质化。群落层面性状的变化反映了该地点其他地方报道的分类变化。在物种水平上，预测物种海拔和丰度变化的三个性状中有两个是地下性状（低菌根分数和浅根）。 这些发现强调了根性状的重要性，其与叶质量分数一起与四十年来分布和丰度的变化相关。群落层面的性状变化在海拔和时间梯度上基本相似。相比之下，通常与群落水平较低海拔相关的特征并不能预测物种之间丰度或分布变化的差异，表明物种和群落水平反应之间的脱钩。总体而言，变化与气候变暖和氮可用性增加的一些影响是一致的。