In vivo analysis of rapid chlorophyll fluorescence induction effects:: aspects relating to the study of bryophytes

A comparison was made between the rapid fluorescence induction characteristics of bryophytes (mosses, liverworts and hornworts), vascular plants and a microalga under actinic irradiation. The bryophytes studied showed similar induction characteristics to microalgae, with a fast decline from an initial peak (P) to a quasi-stationary fluorescence yield (S). Dark relaxation characteristics of the bryophytes were also comparable with those of algae, showing a rapid decline in fluorescence to the F. value when actinic light was switched off. The degree and duration of the P/S decline was related to the intensity of actinic irradiation, although with increasing irradiance the ratio of P/S remained constant for most species. When actinic light was supplied with no prior dark relaxation, the initial peak (P) was suppressed after registration of the first I-P-S cycle, indicating a dependence of the induction characteristics on the oxygen status of the organism. The implication of these observations of oxygen-dependent electron flow in furthering our understanding of bryophyte photosynthetic physiology is discussed.