Development of acute frost drought in Rhododendron ferrugineum at the alpine timberline.

Acute winter frost drought in Rhododendron ferrugineum at the alpine timberline was provoked by removing the snow that had covered the shrubs and by irradiating and rewarming the twigs in situ in a climatized chamber simulating snow melt conditions. Water potential decreased to -2.3 MPa within three days. After activation of photosynthesis on the 1st day, the COr-uptake decreased during the 2nd day and approached zero at the 3rd day. With advanced desiccation, the internal COr concentration of the leaves increased indicating an impairment of chloroplast functions. The procedure of the disturbances appears to be similar to that of other acute drought events.