Given that the ecological niche of tree species is typically narrower for earlier life stages, intraspecific genetic variation at early fitness traits may greatly influence the adaptive response of tree populations to changing environmental conditions. In this study, we evaluated genetic variation in early fitness traits among 12 populations of Betula pendula from a wide latitudinal range in Europe (41-55ºN). We first conducted a chamber experiment to test for population differences in germination and the effect of prechilling treatment on seed dormancy release. We then established three common gardens spread across the species latitudinal range in order to evaluate levels of quantitative genetic variation and genotype-by-environment interaction at different early-life traits. Our results showed significant variation in chamber germination rates among populations (0-60%), with southern populations exhibiting lower germination. Prechilling treatments did not generally improve germination success. Population seedling emergence rates in the field were correlated with chamber germination rates, though being an order of magnitude lower, with an average ranging from 0 to 1.3% across gardens. Highly significant variation was found in field emergence rates among populations, and between seed-crop years within populations, but not among families within populations. Populations differed in seedling height, diameter, slenderness and budburst date, with significant among-family variation. Population latitude was positively associated with chamber germination rate and with seedling emergence rate in one of the central field sites. Overall, genetic, environmental and demographic factors seem to influence the observed high levels of variation in early fitness traits among B. pendula populations. Our results suggest limited regeneration capacity for the study species under drier conditions, but further field trials with sufficient replication over environments and seed crops will improve our understanding of its vulnerability to climate change.

中文翻译：

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欧洲白桦种群（Betula pendula）早期适应性状的遗传变异。

鉴于树木物种的生态位通常在生命的早期阶段较窄，因此早期适应性状的种内遗传变异可能会极大地影响树木种群对变化的环境条件的适应性反应。在这项研究中，我们评估了12个西南桦种群的早期适应性状的遗传变异。来自欧洲的宽纬度范围（41-55ºN）。我们首先进行了一项室内试验，以测试种群发芽的差异以及预冷处理对种子休眠释放的影响。然后，我们建立了三个跨整个物种纬度范围的普通花园，以评估不同早期生命特征的定量遗传变异水平和基因型-环境相互作用。我们的结果表明，不同种群之间的房间萌发率差异很大（0-60％），而南部种群的萌发率较低。预冷处理通常不能提高发芽成功率。田间种群幼苗出苗率与室萌发率相关，尽管降低了一个数量级，但整个花园的平均值为0-1.3％。在种群之间以及种群内种子作物年之间，但在种群内家庭之间，田间出苗率差异非常大。种群的幼苗高度，直径，细长度和芽期不同，家庭间差异很大。在一个中心田地中，种群的纬度与室内萌发率和幼苗出苗率呈正相关。总体而言，遗传，环境和人口因素似乎会影响观察到的早期健身性状的高水平变异 家庭间差异很大。在一个中心田地中，种群的纬度与室内萌发率和幼苗出苗率呈正相关。总体而言，遗传，环境和人口因素似乎会影响观察到的早期健身性状的高水平变异 家庭间差异很大。在一个中心田地中，种群的纬度与室内萌发率和幼苗出苗率呈正相关。总体而言，遗传，环境和人口因素似乎会影响观察到的早期健身性状的高水平变异B. pendula种群。我们的结果表明，在较干燥的条件下，该研究物种的再生能力有限，但进一步的田间试验在环境和种子作物上具有足够的复制能力，将使我们更加了解其对气候变化的脆弱性。