Effects of Cadmium on Laminaria saccarina in Culture

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Abstract
Cd effects were tested on 50 day old laboratory-grown spororophytes of the kelp L. saccharina under continuous-flow laboratory conditions. In standard 6 day experiments, the rapid rate of growth of the plants (30% length increase day-1 in controls) provided a suitable parameter for the measurement of Cd effects. Over a 6 day period a concentration of 4.5 ppm Cd was lethal. A lower concentration might be lethal over a longer period of exposure. In the range of 0.2-4.5 ppm Cd the reduction in growth rate with increasing Cd concentration was nearly linear. The growth rate diminished to 50% of the controls at .apprx. 2.15 ppm Cd. When plants exposed to Cd for 6 days were measured after a further 8 days in unpolluted seawater, the concentration causing growth-rate reduction to 50% of the controls was 0.86 ppm Cd. Long-term aftereffects are more serious than is immediately evident and exposure time is more important than concentration. Cd uptake begins almost immediately and is apparently unregulated, indicating potentially very high tissue concentrations. Over 100 ng Cd mg dry wt-1 was accumulated by plants in 6 days from a 0.78 ppm Cd solution. Saturation was not reached. Relatively more Cd is taken up from lower ambient concentrations. Slower-growing plants and slower-growing regions of the thallus (stipe/holdfast; distal blade region) take up relatively more Cd. At concentrations > 2.3 ppm Cd the blades show a sharply delimited distal loss of pigment. Cd inhibits photosynthesis and dark C assimilation. The degree of inhibition depends on time and concentration. In distal plant regions the photosynthetic potential is more sensitive to Cd. The reduction in photosynthesis in the most actively growing region with increasing Cd concentration follows a curve very similar to that for the reduction in growth. The decrease in growth and photosynthetic potential caused by Cd is not correlated with pigment loss or Cd accumulation.