Department of Plant Sciences, Norwegian University of Life Sciences Ås, Norway.
Department of Arctic and Marine Biology, University of Tromsø Tromsø, Norway.
Front Plant Sci. 2014 Dec 9;5:691. doi: 10.3389/fpls.2014.00691. eCollection 2014.
Young seedlings of the conifer Norway spruce exhibit short day (SD)-induced cessation of apical growth and bud set. Although different, constant temperatures under SD are known to modulate timing of bud set and depth of dormancy with development of deeper dormancy under higher compared to lower temperature, systematic studies of effects of alternating day (DT) and night temperatures (NT) are limited. To shed light on this, seedlings of different provenances of Norway spruce were exposed to a wide range of DT-NT combinations during bud development, followed by transfer to forcing conditions of long days (LD) and 18°C, directly or after different periods of chilling. Although no specific effect of alternating DT/NT was found, the results demonstrate that the effects of DT under SD on bud set and subsequent bud break are significantly modified by NT in a complex way. The effects on bud break persisted after chilling. Since time to bud set correlated with the daily mean temperature under SD at DTs of 18 and 21°C, but not a DT of 15°C, time to bud set apparently also depend on the specific DT, implying that the effect of NT depends on the actual DT. Although higher temperature under SD generally results in later bud break after transfer to forcing conditions, the fastest bud flush was observed at intermediate NTs. This might be due to a bud break-hastening chilling effect of intermediate compared to higher temperatures, and delayed bud development to a stage where bud burst can occur, under lower temperatures. Also, time to bud burst in un-chilled seedlings decreased with increasing SD-duration, suggesting that bud development must reach a certain stage before the processes leading to bud burst are initiated. The present results also indicate that low temperature during bud development had a larger effect on the most southern compared to the most northern provenance studied. Decreasing time to bud burst was observed with increasing northern latitude of origin in un-chilled as well as chilled plants. In conclusion, being a highly temperature-dependent process, bud development is strongly delayed by low temperature, and the effects of DT is significantly modified by NT in a complex manner.
年轻的挪威云杉针叶树幼苗表现出短日（SD）诱导的顶端生长停止和芽休眠。尽管不同，恒定的 SD 温度已知会随着温度的升高而调节芽休眠的时间和深度，与较低温度相比，发展更深的休眠，系统研究交替日（DT）和夜间温度（NT）的影响是有限的。为了阐明这一点，不同来源的挪威云杉幼苗在芽发育过程中暴露于广泛的 DT-NT 组合下，然后直接或在不同的冷却期后转移到长日（LD）和 18°C 的强制条件下。尽管没有发现交替 DT/NT 的特定影响，但结果表明，SD 下 DT 对芽休眠和随后芽休眠的影响以复杂的方式被 NT 显著修饰。休眠后芽休眠的影响仍然存在。由于芽休眠的时间与 SD 下 18 和 21°C 的 DT 下的日平均温度相关，但与 15°C 的 DT 无关，因此芽休眠的时间显然也取决于特定的 DT，这意味着 NT 的影响取决于实际的 DT。尽管 SD 下较高的温度通常会导致转移到强制条件后芽休眠的时间延迟，但在中等 NT 下观察到最快的芽休眠。这可能是由于与较高温度相比，中等温度下的休眠促进了冷却效应，以及在较低温度下，芽休眠延迟到可以发生芽爆发的阶段。此外，未经冷却的幼苗中芽爆发的时间随着 SD 持续时间的增加而减少，这表明在启动芽爆发的过程之前，芽休眠必须达到一定的阶段。本研究结果还表明，在芽发育过程中，低温对最南部的种源比对最北部的种源有更大的影响。未经冷却和冷却的植物中，随着起源的纬度向北增加，观察到芽休眠时间减少。总之，作为一个高度依赖温度的过程，低温强烈延迟芽休眠，DT 的影响以复杂的方式被 NT 显著修饰。
