Life at 0 °C: the biology of the alpine snowbed plant Soldanella pusilla
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.
KeywordsAnatomy Development Growth Low temperature Non-structural carbohydrates Phenology Tissue formation
We thank Sandra Schmid for carbohydrate (NSC) analysis in the lab, Patrick Möhl and Sven Trecco for field assistance and Rolf Siegwolf (PSI, Brugg, Switzerland) for mass-spectrometer data. The Alpine Research and Education Station (ALPFOR) on Furka Pass provided the essential local infrastructure.
CK designed the study, conducted the field- and phytotron-work, and wrote the manuscript. EH helped with field work, provided macro-photographs, and contributed to the manuscript. SR conducted the light microscopy work and contributed the artwork. TK provided Raman spectroscopy scans, which would not have been possible unless FS managed to obtain microtome cuts of unembedded stem tissue and he verified lignification histochemically. AR and JW provided chromatography data for Table 3.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The work for this paper meets all ethical standards.
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