Abstract Past studies indicate that narrower conduits such as those in diffuse-porous species are less vulnerable to freeze-thaw (FT) induced embolism and also facilitate the refilling of embolized xylem conduits early in the spring, resulting in an earlier bud break. In this study, we investigated if a novel environmental condition associated with climate change-induced northward migration will affect the vulnerability to FT-induced embolism and spring phenology in white birch. Seedlings were grown under ambient (400 μmol mol−1) or elevated CO2 concentration (1000 μmol mol−1), and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58 °N latitude. We found that the longest photoperiod (corresponding to 58 °N latitude) significantly increased the maximum specific hydraulic conductivity of the stem. CO2 concentration ([CO2]) and photoperiod had no significant impact on the vulnerability to FT-induced embolism. The treatment of 5 freeze-thaw cycles (+5 to −20 °C) led to an 11 % loss of hydraulic conductivity in dormant seedlings that had been stored at −4 °C for 3 months while the effect of such a treatment in the fall was much smaller. This result suggests that freeze-thaw events in late winter or spring can impair the hydraulic conductivity of the xylem which in turn may negatively affect the physiology of the trees. Indeed, the FT treatment in this study delayed budburst and leaf expansion in the spring. It is interesting to note that photoperiods had the opposite effect on budburst under different [CO2]: longer photoperiods led to earlier budburst in the spring under elevated [CO2], but delayed budburst under ambient [CO2]. The synergistic effect of longer photoperiods and CO2 elevation suggests that the growing season for white birch may be longer than what we predict from either factor alone at a migration site in the future when [CO2] will be much higher.

中文翻译：

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冻融事件延迟了春季萌芽和叶片扩张，而较长的光周期在不同 [CO2] 白桦树中具有相反的影响：在高架下推进，但在环境 [CO2] 下延迟

摘要 过去的研究表明，较窄的管道，如散孔物种中的管道，不易受到冻融 (FT) 诱发的栓塞的影响，并且还有助于在春季早期重新填充栓塞的木质部管道，从而导致更早的萌芽。在这项研究中，我们调查了与气候变化引起的向北迁移相关的新环境条件是否会影响白桦对 FT 引起的栓塞和春季物候的脆弱性。幼苗在环境 (400 μmol mol-1) 或升高的 CO2 浓度 (1000 μmol mol-1) 和对应于 48（种子起源）、52、55 和 58 °N 纬度的四种光周期制度下生长。我们发现最长的光周期（对应于 58 °N 纬度）显着增加了茎的最大比水力传导率。CO2 浓度 ([CO2]) 和光周期对 FT 引起的栓塞的脆弱性没有显着影响。5 个冻融循环（+5 至 -20 °C）的处理导致休眠幼苗在 -4 °C 下储存 3 个月的水力传导率损失 11%，而这种处理的效果在下降要小得多。这一结果表明，冬末或春季的冻融事件会损害木质部的水力传导性，进而可能对树木的生理机能产生负面影响。事实上，本研究中的 FT 处理延迟了春季的芽芽和叶片扩张。有趣的是，光周期对不同 [CO2] 下的萌芽有相反的影响：在升高的 [CO2] 下，较长的光周期导致春季萌芽提前，但在环境 [CO2] 下会延迟萌芽。