PHYSIOLOGICAL TOLERANCE OF CAMELLIA-RUSTICANA LEAVES TO HEAVY SNOWFALL ENVIRONMENTS - THE EFFECTS OF PROLONGED SNOW COVER ON EVERGREEN LEAVES

Camellia rusticana is an evergreen broad-leaved shrub found only in ar eas of heavy snowfall in Japan. The ecophysiological tolerance of this species to prolonged snow cover was studied in comparison with those of Camellia japonica found in areas of light snowfall. The shoots of C . rusticana and C. japonica were stored under a simulated snow cover f or 1 year. During the experimental period, about 20% of the leaves of C. japonica defoliated after 90-140 days of storage and more than 80% of the leaves browned within 360 days. The proliferation of fungi was observed on all shoots of C. japonica after 200 days. In contrast, the leaves of C. rusticana showed no visible changes throughout the exper imental period. The decline in the rate of soluble carbohydrate conten t in C. rusticana was about one-sixth of that in C. japonica. The phot osynthetic capacity (O-2 exchange rates at saturated light and CO2 at 20 degrees C) of C. japonica dropped to about half its initial value a fter 140 days, while that of the C. rusticana did not change even afte r 360 days. Under dark conditions, the stomata of C. rusticana were al ways closed through the experiment, but those of C. japonica were not completely closed after 90 days. The differences in stomata characteri stics and the consumption rate of soluble carbohydrates under snow-cov ered conditions between the two Camellia species are important factors for determining their habitat segregation by snow depth.