On the Osmotic Pressure and Resistance to Desiccation of Epiphytic Mosses From a Beech Forest, South-West Japan

Abstract

Measurements are given of the vertical range of the predominant epiphytic moss species which form tufts on 2 trees of Fagus crenata on Mt. Hiko, S.W. Japan, one at 930 m altitude and the other at 1160 m altitude. With increasing altitude, some alteration is observed in the type of vertical range displayed by moss tufts. There is in general a correlation between the osmotic values of the leaf-cells, (which range from about 0.6 atmospheres to about 1.7 atmosphere), and the limits of vertical distribution of the species on the trees. The resistance of each species to desiccation was expressed in terms of the length in days of the period of survival of shoots in containers maintained at constant levels of relative humidity ranging from saturation to absolute dryness. At relative humidities between about 30% and 70%, 3 types of resistance were shown: 1st, species belonging to the trunk bases died quickly, e.g., Hylocomium cavifolium and Thuidium cymbifollum; 2nd, species growing mainly higher on the trunks survived longer, e.g. Anomodon giraldii and Neckera yezoana; 3rd, species of the upper parts of the trunk and boughs remained alive at the end of the experiments, e.g. Boulaya mlttenii. The resistance of epiphytic mosses to desiccation becomes greater in winter than in summer, a fact which may relate to their physiological activity.