Conservation Science Department, Royal Botanic Gardens Kew, Millennium Seed Bank, Wakehurst, Ardingly, West Sussex, UK.
School of Agriculture, Policy and Development, University of Reading, Earley Gate, Reading RG6 6AR, UK.
Ann Bot. 2020 Jun 1;125(7):1013-1023. doi: 10.1093/aob/mcaa025.
Understorey species in temperate deciduous woodlands such as wild daffodil (Narcissus pseudonarcissus) and common snowdrop (Galanthus nivalis) have complex dormancy: seeds that are shed in late spring require warm summer temperatures for embryo elongation and dormancy alleviation, but then cooler temperatures for germination in autumn. As seasons warm and tree canopies alter, how will different seasonal temperature sequences affect these complex dormancy responses?
The effect of different sequences of warmer (+5 °C), current or cooler (-5 °C) seasons (summer to spring) on seed germination patterns over seven successive seasons were investigated, with all sequences combined factorially to determine the consequences of differential seasonal temperature change for the temporal pattern of germination (and so seedling recruitment).
Little (<1 %, G. nivalis) or no (N. pseudonarcissus) seed germination occurred during the first summer in any treatment. Germination of N. pseudonarcissus in the first autumn was considerable and greatest at the average (15 °C) temperature, irrespective of the preceding summer temperature; germination was also substantial in winter after a warmer autumn. Germination in G. nivalis was greatest in the warmest first autumn and influenced by preceding summer temperature (average > warmer > cooler); the majority of seeds that germinated over the whole study did so during the two autumns but also in year 2's cooler summer after a warm spring.
Warmer autumns and winters delay first autumn germination of N. pseudonarcissus to winter but advance it in G. nivalis; overall, warming will deplete the soil seed bank of these species, making annual seed influx increasingly important for recruitment and persistence. This study provides a comprehensive account of the effects of temperature changes in different seasons on seed germination in these early spring-flowering geophytes and consequently informs how these and other temperate woodland species with complex seed dormancy may respond to future climate change.
温带落叶林地中的林下物种，如野生水仙花（Narcissus pseudonarcissus）和普通雪花莲（Galanthus nivalis），具有复杂的休眠特性：春季晚期脱落的种子需要温暖的夏季气温来促进胚伸长和休眠缓解，但随后在秋季需要更凉爽的温度来发芽。随着季节变暖和树冠变化，不同季节温度序列将如何影响这些复杂的休眠反应？
研究了不同季节温度序列（夏季到春季变暖+5°C、当前或变冷-5°C）对连续七个季节种子发芽模式的影响，所有序列均进行组合因子分析，以确定季节性温度变化对发芽时间模式（因此对幼苗补充）的影响。
在任何处理中，第一个夏季中种子的发芽率都很低（<1%，G. nivalis）或没有（N. pseudonarcissus）。N. pseudonarcissus 在第一个秋季的发芽率相当高，在平均（15°C）温度下最大，而与前一个夏季温度无关；在温暖的秋季之后，冬季的发芽率也相当高。G. nivalis 的发芽率在最温暖的第一个秋季最大，并受前一个夏季温度的影响（平均>温暖>凉爽）；在整个研究过程中，大多数发芽的种子在两个秋季发芽，但也在温暖春季后的凉爽夏季的第二年发芽。
温暖的秋季和冬季会延迟 N. pseudonarcissus 在第一个秋季的发芽时间至冬季，但会提前在 G. nivalis 中发芽；总体而言，变暖将耗尽这些物种的土壤种子库，使年度种子流入对补充和生存变得越来越重要。本研究全面描述了不同季节温度变化对这些早春开花的球茎植物种子发芽的影响，从而为了解这些和其他具有复杂种子休眠的温带林地物种如何应对未来气候变化提供了信息。
