• Cadmium;
  • chlorophyll;
  • mercury;
  • methyl-Hg;
  • photosynthesis;
  • transpiration;
  • water content;
  • zinc

Spruce seedlings [Picea abies (L.) Karst.] were exposed to a range of concentrations of Zn, Cd, Hg and methyl-Hg for 5 weeks. The chlorophyll and water content of the needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plant were determined using a Li-cor portable photosynthesis measuring system. Chlorophyll and water contents of needles decreased in response to all metal treatments, as did CO2 uptake. At 1 μM Cd, 0.1 μM Hg and 30 and 60 μM Zn, the decrease in CO2 uptake could be accounted for by decreased chlorophyll concentrations. Decreased transpiration was only found at 5 μM Cd and 0.01 μM methyl-Hg. At 5 μM Cd most of the decrease in CO2 uptake could be explained by decreased chlorophyll levels and stomatal closure induced by water stress. At 0.01 μM methyl-Hg, besides a decrease in chlorophyll concentration and partial stomatal closure, photosynthetic reactions may have been directly affected. Respiration rates were not influenced by exposure to heavy metals.