All plant species reach a low temperature range limit when either low temperature extremes exceed their freezing tolerance or when their metabolism becomes too restricted. In this study, we explore the ultimate thermal limit of plant tissue formation exemplified by a plant species that seemingly grows through snow. By a combination of studies in alpine snowbeds and under controlled environmental conditions, we demonstrate and quantify that the clonal herb Soldanella pusilla (Primulaceae) does indeed grow its entire flowering shoot at 0 °C. We show that plants resume growth under 2–3 m of snow in mid-winter, following an internal clock, with the remaining period under snow until snow melt (mostly in July) sufficient to produce a flowering shoot that is ready for pollination. When snow pack gets thin, the flowering shoot intercepts and re-radiates long-wave solar radiation, so that snow and ice gently melt around the fragile shoot and the flowers emerge without any mechanical interaction. We evidence bud preformation in the previous season and enormous non-structural carbohydrate reserves in tissues (mainly below ground) in the form of soluble sugars (largely stachyose) that would support basic metabolism for more than 2 entire years under snow. However, cell-wall formation at 0 °C appears to lack unknown strengthening factors, including lignification (assessed by confocal Raman spectroscopy imaging) that require between a few hours or a day of warmth after snow melt to complete tissue strengthening. Complemented with a suite of anatomical data, the work opens a window towards understanding low temperature limits of plant growth in general, with potential relevance for winter crops and trees at the natural climatic treeline.

中文翻译：

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0°C时的生命：高山雪床植物Soldanella pusilla的生物学

当低温极限超过其冷冻耐受性或它们的新陈代谢变得过于受限时，所有植物物种均达到低温范围极限。在这项研究中，我们探索了植物组织形成的最终温度极限，例如看起来像是在雪中生长的植物物种。通过对高山雪床和受控环境条件下的研究相结合，我们证明并量化了克隆药草Soldanella pusilla（樱草科）确实确实在0°C下生长了整个开花枝。我们表明，在内部时钟之后，植物在冬季中旬在2–3 m的雪中恢复生长，其余时间在雪中直至雪融化（大部分在7月），足以产生准备授粉的开花芽。当积雪变薄时，开花的枝条会截获并重新辐射长波太阳辐射，因此，雪和冰在脆弱的枝条周围轻轻融化，而花朵则没有任何机械相互作用。我们证明了前一个季节的芽形成和组织中（主要是地下的）组织中大量非结构性碳水化合物的储存（以可溶性糖（主要是水苏糖）的形式），可在雪下支持超过2年的基本代谢。然而，0°C时的细胞壁形成似乎缺乏未知的增强因子，包括木质化（通过共焦拉曼光谱成像评估），融雪后需要几个小时或一天的温暖才能完成组织增强。与一系列解剖学数据相辅相成，这项工作为了解一般植物生长的低温极限打开了一个窗口，该极限与自然气候树线下的冬季作物和树木具有潜在的相关性。