• Early-stage fitness variation has been seldom evaluated at broad scales in forest tree species, despite the long tradition of studying climate-driven intraspecific genetic variation. In this study, we evaluated the role of climate in driving patterns of population differentiation at early-life stages in Pinus sylvestris and explored the fitness and growth consequences of seed transfer within the species range.
• We monitored seedling emergence, survival and growth over a 2-yr period in a multi-site common garden experiment which included 18 European populations and spanned 25° in latitude and 1700 m in elevation.
• Climate–fitness functions showed that populations exhibited higher seedling survival and growth at temperatures similar to their home environment, which is consistent with local adaptation. Northern populations experienced lower survival and growth at warmer sites, contrary to previous studies on later life stages. Seed mass was higher in populations from warmer areas and was positively associated with survival and growth at more southern sites. Finally, we did not detect a survival–growth trade-off; on the contrary, bigger seedlings exhibited higher survival probabilities under most climatic conditions.
• In conclusion, our results reveal that contrasting temperature regimes have played an important role in driving the divergent evolution of P. sylvestris populations at early-life stages.

中文翻译：

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樟子松早期对温度和降水变化的适应性响应

• 尽管研究气候驱动的种内遗传变异有着悠久的传统，但很少对森林树种的早期适应度变异进行广泛的评估。在这项研究中，我们评估了气候在推动樟子松早期种群分化模式中的作用，并探讨了物种范围内种子转移的适应性和生长后果。
• 我们在一个多地点公共花园试验中监测了 2 年期间的幼苗出苗、存活和生长，该试验包括 18 个欧洲种群，纬度跨度为 25°，海拔高度为 1700 m。
• 气候适应度函数表明，种群在与其家庭环境相似的温度下表现出更高的幼苗存活率和生长率，这与当地适应是一致的。与之前对生命后期阶段的研究相反，北方人口在较温暖的地区经历了较低的存活率和生长率。来自温暖地区的种群的种子质量更高，并且与更南部地区的存活和生长呈正相关。最后，我们没有发现生存-增长的权衡。相反，在大多数气候条件下，更大的幼苗表现出更高的存活率。
• 总之，我们的结果表明，不同的温度制度在推动P. sylvestris种群在生命早期阶段的分化进化方面发挥了重要作用。