• chlorophyll concentration;
  • chlorophyll a/b ratios;
  • desiccation;
  • irradiance;
  • mosses


Leaves of shade plants typically have higher concentrations, and lower a/b ratios of chlorophyll than do leaves of sun plants. In poikilohydric mosses as in vascular plants, such differences in concentration have been interpreted either as adaptations which enhance light capture or, in the more exposed mosses, as degradation of chlorophyll owing to water stress. There were no significant correlations between degree of hydration and either concentration or a/b ratios of chlorophyll in tissues of Leucobryum glaucum (Hedw.) Angustt. ex Fr. and Thuidium delicatulum (Hedw.) B.S.G. exposed to increasing water stress. As these data do not support the latter hypothesis, it is concluded that the former explanation is probably valid.