Past research suggests climate change will cause the climate envelopes of various tree species to shift to higher latitudes and can lead to a northward migration of trees. However, the success and scope of the migration are likely affected by factors that are not contained in the climate envelope, such as photoperiod and interactive effects of multiple environmental factors, and these effects are currently not well understood. In this study, we investigated the interactive effects of CO₂ concentrations ([CO₂]), photoperiod and soil moisture on the morphological and physiological traits of Populus tremuloides Michx. We grew seedlings under two levels of [CO₂] (ambient [CO₂] (AC) 400 vs elevated [CO₂] (EC) 1000 μmol mol⁻¹), four photoperiod regimes (growing season photoperiods at 48 (seed origin), 52, 55 and 58°N latitude) and two soil moisture regimes (high soil moisture (HSM) vs low soil moisture (LSM), −2 MPa) for two growing seasons in greenhouses. Both morphological and physiological responses were observed. Low soil moisture reduced leaf size, total leaf area and height growth by 33, 46 and 12%, respectively, and increased root/shoot ratio by 20%. The smaller leaf area and increased root/shoot ratio allowed the seedlings in LSM to maintain higher the maximum rate of Rubisco carboxylation (V_cmax) and the maximum rate of electron transport for RuBP regeneration (J_max) than control seedlings (55 and 83% higher in July, 52 and 70% in August, respectively). Photoperiod and [CO₂] modified responses to LSM and LSM altered responses to photoperiod and [CO₂], e.g., the August photosynthetic rate was 44% higher in LSM than in HSM under EC but no such a difference existed under AC. The increase in V_cmax and J_max in response to LSM varied with photoperiod (V_cmax: 36% at 52°N, 22% at 55°N, 47% at 58°N; J_max: 29% at 52°N, 21% at 55°N, 45% at 58°N). Stomatal conductance and its reduction in response to LSM declined with increasing photoperiod, which can have significant implications for soil moisture effect on northward migration. This study highlights the need to consider the complex interactions of [CO₂], photoperiod and soil moisture when planning assisted migration or predicting the natural migration of boreal forests in the future.

中文翻译：

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在发抖的白杨中，光周期和CO2升高会影响干旱的形态和生理响应：对气候变化导致的迁徙的影响。

过去的研究表明，气候变化将导致各种树木的气候范围向更高的纬度转移，并可能导致树木向北迁移。但是，迁移的成功和范围很可能受到气候包络中未包含的因素的影响，例如光周期和多种环境因素的相互作用，目前尚不十分了解这些影响。在这项研究中，我们调查了CO ₂浓度（[CO ₂ ]），光周期和土壤水分对胡杨的形态和生理特性的相互作用。我们在[CO ₂ ]的两个水平下生长幼苗（环境[CO ₂ ]（AC）400与升高的[CO₂ ]（EC）1000μmolmol ^-1），四种光周期模式（生长季节在48（种子起源），北纬52、55和58°N的光周期）和两种土壤湿度模式（高土壤湿度（HSM）与低土壤湿度湿度（LSM），-2 MPa）在温室中生长两个季节。观察到形态学和生理学反应。低的土壤水分使叶的大小，叶的总面积和高度的增长分别减少33％，46％和12％，并使根/枝比率增加20％。较小的叶面积和增加的根/茎比使LSM的幼苗能够保持较高的Rubisco羧化最大速率（V _cmax）和RuBP再生的最大电子传递速率（J _max）比对照幼苗（7月分别增加55％和83％，8月分别增加52％和70％）。光周期和[CO ₂ ]改性反应，LSM和LSM改变响应光周期和[CO ₂ ]，例如，八月光合速率在LSM高于EC下HSM 44％，但AC下不存在任何这样的差别。响应LSM的V _cmax和J _max的增加随光周期的变化而变化（V _cmax：在52°N时为36％，在55°N时为22％，在58°N时为47％; J _max：52°N时为29％，55°N时为21％，58°N时为45％）。随着光周期的增加，气孔电导及其对LSM的响应降低，这可能对土壤水分对北向迁移的影响具有重要意义。这项研究强调了在计划将来的辅助迁移或预测北方森林的自然迁移时，需要考虑[CO ₂ ]，光周期和土壤水分的复杂相互作用。