Ice Propagation in Dehardened Alpine Plant Species Studied by Infrared Differential Thermal Analysis (IDTA)

Abstract

Infrared differential thermal analysis (IDTA) was used to study ice propagation and whole plant freezing patterns in dehardened intact individuals of various alpine plant species, including a shrub (Rhododendron ferrugineum), a herbaceous plant (Senecio incanus), a cushion plant (Silene acaulis), and two graminoids (Poa alpina and Juncus trifidus). Freezing patterns differed markedly among species and reflected peculiarities of the shoot structure and the vascular system. In graminoids, each single leaf required a separate ice nucleation event, as the polystele prevents ice propagation between leaves via the stem. Additionally, enhanced supercooling resulted in a temperature range of whole plant freezing of up to 10°C, which corroborates the high summer frost resistance of graminoids. This could have ecological significance for frost survival. In contrast, in dicotyledonous species one nucleation event was usually sufficient for whole plant freezing. Controlled ice-seeding experiments on leaves with droplets of water and bacterial water suspension (Pseudomonas syringae) showed that ice propagation into the leaf tissue from the surface was inhibited as long as the leaves were undamaged. The rate of ice propagation in veins was significantly higher at lower temperatures and reached up to 24 cm s−1 in J. trifidus, which is much higher than reported in earlier findings. Ice propagation in graminoids was much faster, which may indicate that ice propagates within the protoxylem lacunae of large vessels.