Abstract
Ranunculus glacialis grows and reproduces successfully, although the snow-free time period is short (2–3 months) and night frosts are frequent. At a nival site (3185 m a.s.l.), we disentangled the interplay between the atmospheric temperature, leaf temperatures, and leaf freezing frequency to assess the actual strain. For a comprehensive understanding, the freezing behavior from the whole plant to the leaf and cellular level and its physiological after-effects as well as cell wall chemistry were studied. The atmospheric temperatures did not mirror the leaf temperatures, which could be 9.3 °C lower. Leaf freezing occurred even when the air temperature was above 0 °C. Ice nucleation at on average −2.6 °C started usually independently in each leaf, as the shoot is deep-seated in unfrozen soil. All the mesophyll cells were subjected to freezing cytorrhysis. Huge ice masses formed in the intercellular spaces of the spongy parenchyma. After thawing, photosynthesis was unaffected regardless of whether ice had formed. The cell walls were pectin-rich and triglycerides occurred, particularly in the spongy parenchyma. At high elevations, atmospheric temperatures fail to predict plant freezing. Shoot burial prevents ice spreading, specific tissue architecture enables ice management, and the flexibility of cell walls allows recurrent freezing cytorrhysis. The peculiar patterning of triglycerides close to ice rewards further investigation.
Highlights
In the nival life zone, the snow-free time slot is short, not exceeding 2–3 months [1,2]
At our investigation site in the nival zone, atmospheric temperatures insufficiently describe the environmental strain of leaves of R. glacialis
Ranunculus glacialis is outstanding in maintaining a high degree of freezing resistance during the reproduction growth period
Summary
In the nival life zone, the snow-free time slot is short, not exceeding 2–3 months [1,2]. During this time, freezing temperatures are frequent. At 3450 m a.s.l. on Mt. Brunnenkogel (Pitztal Glacier) in a canopy of Ranunculus glacialis, night frosts were recorded on 68% of 74 snow-free nights [4]. Brunnenkogel (Pitztal Glacier) in a canopy of Ranunculus glacialis, night frosts were recorded on 68% of 74 snow-free nights [4] After such nights, plants can be found stiffly frozen in the morning. In the nival life zone, the environmental forces driving the leaf temperature below air temperature may be even stronger. The leaf temperatures of nival plants close to their upper elevational distribution range have not been recorded, it is inevitably necessary to gain insight into frost survival
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