Abstract Trees may migrate northward in response to climate change, which would expose them to different environmental conditions, such as [CO2], photoperiod, soil moisture. Changes in these environmental conditions will likely influence tree phenology and growth. We grew Populus tremuloides Michx. from seeds for two growing seasons under two [CO2] (400 vs 1000 μmol mol−1), four photoperiod regimes (corresponding to 48 °N (seed origin), 52 °N, 55 °N, and 58 °N latitude), two soil moistures (60 %–75 % vs 13 %–20 %) and examined phenological responses. We found that longer photoperiods extended growing season by delaying autumnal phenology and increased growth. Low moisture also delayed autumnal phenology but reduced growth, and the effects were reduced by elevated [CO2]. Surprisingly, low moisture reduced cold hardiness of aspen. Elevated [CO2] delayed bud break in the spring and the effects were magnified by the low moisture. The interactive effects of photoperiod, CO2, and soil moisture on phenology, cold hardiness, growth, and growing season indicate the complex nature of northward migration that has been predicated under the scenario of climate change. Our results suggest that these interactions should be considered when planning latitudinal seed transfers and predicting the migration of boreal trees in response to climate change.

中文翻译：

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光周期、[CO2] 和土壤水分相互作用影响颤杨的物候：对气候变化引起的迁移的影响

摘要 树木可能会因气候变化而向北迁移，这会使它们暴露于不同的环境条件，如 [CO2]、光周期、土壤湿度。这些环境条件的变化可能会影响树木物候和生长。我们种植了Populus tremuloides Michx。在两个 [CO2]（400 对 1000 μmol mol-1）、四个光周期制度（对应于 48 °N（种子起源）、52 °N、55 °N 和 58 °N 纬度）下的两个生长季节的种子，两种土壤湿度（60 %–75 % vs 13 %–20 %）并检查物候响应。我们发现较长的光周期通过延迟秋季物候和增加生长来延长生长季节。低水分也延迟了秋季物候，但会降低生长，并且 [CO2] 升高降低了影响。令人惊讶的是，低水分降低了白杨的抗寒性。升高的 [CO2] 延迟了春季的萌芽，并且其影响因低水分而被放大。光周期、CO2 和土壤水分对物候、抗寒性、生长和生长季节的交互作用表明，在气候变化情景下预测的向北迁移的复杂性质。我们的结果表明，在规划纬度种子转移和预测北方树木因气候变化而迁移时，应考虑这些相互作用。