Chlorophyll fluorescence as an exploratory tool for ecophysiological studies on mosses and other small poikilohydric plants

Abstract

Photosynthetic pigment content (chlorophylls and carotenoids), slow chlorophyll fluorescence parameters (F_M and F_T at 690 and 735 nm) and net CO₂ assimilation rate were measured in the moss Tortuia ruralis (Hedw.) Gaertn. et al., and the lichens Cladonia convoluta (Lam.) P. Coul. and C. jurcata (Huds.) Schrad.

Chlorophylls, carotenoids and net CO₂ assimilation (P_N) were lower (on a dry-mass basis), and F₆₉₀/F₇₃₅ was higher, in all three cryptogams than average values reported for vascular plants. Within the moss shoots and lichens, chlorophylls, carotenoids, the fluorescence-decrease ratio (Rfd = [F_M–F_T]/F_T) and net photosynthesis (P_N) were higher, and F₆₉₀/F₇₃₅ was lower, in the apical/marginal, younger parts than in the basal, older ones. F₆₉₀/F₇₃₅ was inversely related to chlorophyll a+b, higher values indicating lower chlorophyll content.

There was a good correlation between the Rfd and P_N (measured at optimal water content) in the different parts of the moss and lichens, and in samples of T. ruralis which had been exposed for two months to different levels of atmospheric pollution in a transplant experiment, a correlation also found in published work on the same species in the course of desiccation-remoistening cycles.

Chlorophyll fluorescence provides a non-invasive and relatively quick measure of overall photosynthetic function for ecophysiological studies, using either slow fluorescence kinetics (as here), or measurements from fast or modulated fluorometers.