Varying selection differential throughout the climatic range of Norway spruce in Central Europe

Predicting species distribution changes in global warming requires an understanding of how climatic constraints shape the genetic variation of adaptive traits and force local adaptations. To understand the genetic capacity of Norway spruce populations in Central Europe, we analyzed variation of tree heights at the juvenile stage in common-garden experiments established from the species’ warm-dry to cold-moist distribution limits. We report the following findings: first, 47 % of the total tree-height variation at trial sites is attributable to the tree populations irrespective of site climate. Second, tree height variation within populations is higher at cold-moist trial sites than at warm-dry sites and higher within populations originating from cold-moist habitats than from warm-dry habitats. Third, for tree ages of 7 to 15 years, the variation within populations increases at cold-moist trial sites, whereas it remains constant at warm-dry sites. Fourth, tree-height distributions are right-skewed at cold-moist trial sites, whereas they are non-skewed but platykurtic at warm-dry sites. Our results suggest that in cold environments climatic conditions impose stronger selection and probably restrict the distribution of spruce, whereas at the warm distribution limit, the species’ realized niche might rather be controlled by external drivers, for example forest insects.

预测全球变暖背景下的物种分布变化，需厘清气候限制如何塑造适应性性状的遗传变异，并驱动本地适应过程。为阐明中欧挪威云杉（Norway spruce）种群的遗传潜力，我们以该物种从暖干分布边界至冷湿分布边界的种群为材料，开展同质园实验（common-garden experiments），并分析其幼树阶段的树高变异。本研究报告以下四项发现：其一，试验点内总树高变异的47%可归因于树种种群差异，而非试验点的气候条件；其二，种群内部的树高变异在冷湿试验点高于暖干试验点，且源自冷湿生境的种群内部变异高于源自暖干生境的种群；其三，对于树龄7至15年的个体，冷湿试验点的种群内部变异随树龄增长而升高，而暖干试验点的该变异水平保持稳定；其四，冷湿试验点的树高分布呈右偏态（right-skewed），暖干试验点的树高分布则无偏态但呈扁峰态（platykurtic）。本研究结果表明，在寒冷环境中，气候条件施加了更强的选择压力，并可能限制云杉的分布范围；而在暖干分布边界处，该物种的现实生态位（realized niche）更可能受外部因素调控，例如森林昆虫。