Alpine treelines are expected to shift upward due to climate warming, whereas warmer conditions can have negative impacts on forests located near the xeric, equatorward limit of the distribution of tree species (rear edge). We compare tree populations forming the distribution limits of mountain pine (Pinus uncinata) in north-eastern Spain: two cold-limited alpine treeline populations, and a rear-edge drought-prone stand. In the treelines, trees were sampled in three altitudinal belts to evaluate within-site variations considering the forest, the transitional ecotone and the treeline.

Tree growth was markedly higher in one of the treeline sites (Tesso), particularly in the forest belt, as compared to the other treeline (Las Cutas), and to the warmest rear-edge stand. Tree growth in the rear-edge population depended on June precipitation. Trees presented also comparatively smaller leaves with higher Specific Leaf Area (SLA) there than in the two treelines. Regarding the differences between altitudinal belts within the treelines, treeline soils showed lower N concentrations and a lower content of sand than in forests. Soil microbiota was dominated by bacteria in the treeline and by fungi in the forest, although with differences between sites. Soil characteristics and microbial composition were strongly related, whereas its relationship with tree growth and functional traits was less clear.

The marked differences in leaf traits and growth response to climate found when comparing treeline and rear-edge sites highlights the biogeographical uniqueness of sites forming the equatorward distribution limit. The greater tree growth in the Tesso treeline as compared to Las Cutas indicate that interactions between climate and physical and chemical properties of the soil influence tree growth and its interactions with soil microbial communities in the treeline. A better understanding of plant-soil feedbacks may help to understand the future dynamics of tree populations forming the species’ climatic and geographic limits of distribution.

由于气候变暖，预计高山林线将向上移动，而温暖的条件可能会对位于干旱、赤道附近树种分布限制（后缘）附近的森林产生负面影响。我们比较了西班牙东北部形成山松 ( Pinus uncinata )分布范围的树木种群：两个受寒限制的高山林线种群和一个后缘易干旱的林分。在林线中，在三个海拔带中对树木进行采样，以评估考虑森林、过渡交错带和林线的场地内变化。

与另一条林线 (Las Cutas) 和最温暖的后缘林分相比，其中一个林线 (Tesso) 的树木生长明显更高，特别是在森林带。后缘种群的树木生长取决于六月的降水。与两条林线相比，那里的树木也呈现出相对较小的叶子，具有更高的比叶面积 (SLA)。关于林线内海拔带之间的差异，林线土壤的氮浓度和沙子含量低于森林。土壤微生物群以林中的细菌和森林中的真菌为主，尽管地点之间存在差异。土壤特征和微生物组成密切相关，而其与树木生长和功能性状的关系不太清楚。

比较林线和后缘地点时发现的叶片性状和生长对气候的反应的显着差异突出了形成赤道分布界限的地点的生物地理独特性。与 Las Cutas 相比，Tesso 树线中的树木生长更大，这表明气候与土壤的物理和化学特性之间的相互作用会影响树木的生长及其与树线中土壤微生物群落的相互作用。更好地了解植物-土壤反馈可能有助于了解形成该物种气候和地理分布限制的树木种群的未来动态。