CADMIUM TOLERANCE IN A METAL-CONTAMINATED POPULATION OF THE GRASSLAND MOSS RHYTIDIADELPHUS-SQUARROSUS

Two populations of Rhytidiadelphus squarrosus, from metal-contaminated and uncontaminated habitats, differed in their intra- and extracellular Cd contents but had similar cellular levels of Cu. Moss shoots were supplied with a pulse of toxic metal by incubating in Cu or Cd nitrate solutions and effects on respiration, photosynthesis and intracellular K loss were monitored with time after initial exposure. Increasing intracellular Cu levels correlated most closely with a concurrent decline in intracellular K. Photosynthesis also declined in proportion to intracellular Cu; significant Cu-induced stimulation of respiration was observed. The most significant effect of Cd treatment was a decline in photosynthesis in proportion to the intracellular concentration of Cd. Apical segments from both populations showed similar sensitivity to Cu, whereas the metal-contaminated population showed increased resistance to Cd. Sensitivity to Cd increased in the more basal portions of moss gametophores, indicating that apparent resistance of Cd might reflect shoot Vitality and age effects. After laboratory growth to eliminate differences in the physiological status of apical segments, it was confirmed that the metal-contaminated population of the moss was photosynthetically more tolerant to Cd at intracellular Cd concentrations found to cause considerable photosynthetic inhibition in the uncontaminated population. The metal-contaminated population of the moss that was tolerant to Cd was not cotolerant to Cu.