The reduced growth performance of individuals from range edges is a common phenomenon in various taxa, and considered to be an evolutionary factor that limits the species’ range. However, most studies did not distinguish between two mechanisms that can lead to this reduction: genetic load and adaptive selection to harsh conditions. To address this lack of understanding, we investigated the climatic and genetic factors underlying the growth performance of Betula ermanii saplings transplanted from 11 populations including high-altitude edge and low-latitude edge population. We estimated the climatic position of the populations within the overall B. ermanii’s distribution, and the genetic composition and diversity using restriction-site associated DNA sequencing, and measured survival, growth rates and individual size of the saplings. The high-altitude edge population (APW) was located below the 95% significance interval for the mean annual temperature range, but did not show any distinctive genetic characteristics. In contrast, the low-latitude edge population (SHK) exhibited a high level of linkage disequilibrium, low genetic diversity, a distinct genetic composition from the other populations, and a high relatedness coefficient. Both APW and SHK saplings displayed lower survival rates, heights and diameters, while SHK saplings also exhibited lower growth rates than the other populations’ saplings. The low heights and diameters of APW saplings was likely the result of adaptive selection to harsh conditions, while the low survival and growth rates of SHK saplings was likely the result of genetic load. Our findings shed light on the mechanisms underlying the reduced growth performance of range-edge populations.

分布范围边缘个体的生长性能下降是各种类群中的常见现象，并被认为是限制物种分布范围的进化因素。然而，大多数研究没有区分可能导致这种减少的两种机制：遗传负荷和对恶劣条件的适应性选择。为了解决这一认识的缺乏，我们调查了从高海拔边缘种群和低纬边缘种群等11个种群移植的桦树苗生长性能背后的气候和遗传因素。我们利用限制性位点相关的 DNA 测序估计了整个厄氏芽孢杆菌种群的气候位置，以及遗传组成和多样性，并测量了树苗的存活率、生长率和个体大小。高海拔边缘种群（APW）位于年平均气温范围95%显着性区间以下，但没有表现出任何独特的遗传特征。相比之下，低纬度边缘种群（SHK）表现出高度的连锁不平衡、较低的遗传多样性、与其他种群不同的遗传组成以及较高的相关系数。APW 和 SHK 树苗的成活率、高度和直径均较低，而 SHK 树苗的生长速度也低于其他种群的树苗。APW 树苗的低高度和直径可能是对恶劣条件的适应性选择的结果，而 SHK 树苗的低存活率和生长率可能是遗传负荷的结果。我们的研究结果揭示了范围边缘种群生长性能下降的潜在机制。