Effects of copper, zinc and cadmium on the pigments and photosynthesis of black spruce (Picea mariana (Mill.) B.S.P) seedlings

Abstract

The purpose of this study was to quantify the effects of heavy metals on pigments and photosynthesis in four and a half month old black spruce (Picea mariana (Mill.) B.S.P.) seedlings. Photosynthetic pigment analysis by HPLC and reflectance red edge methods were compared to chi a fluorescence and net oxygen evolution measurements to assess their effectiveness in diagnosing plant stress. Copper, zinc and cadmium were applied as 0, 10 and 20 mM Cu(N03)2, Zn (N03)2 and Cd(N03)2, for 214 weeks. Response to the treatments was examined by measuring pigment content, reflectance red edge, (see document) net oxygen evolution, net water content and needle element content. No treatment differences were found for pigment content or red edge. In contrast, (see document) of seedlings treated with 20 mM Cd was significantly lower than all other treatments and net oxygen evolution decreased m metal-treated seedlings compared to untreated control seedlings. Net water content did not differ between treatments. Needle element content did not change, except for increases m Cu, Zn and Cd in the seedlings treated with these elements. It was concluded that pigment content was unaffected by the treatments but that photosynthetic efficiency (i.e. oxygen evolved) decreased. Possible explanations include inhibition of enzyme activity by Cu2+, Zn2+ and Cd2+, or overloading of defense mechanisms, such as phytochelatins. The use of HPLC analysis of pigments and remote spectroradiometry may prove useful in assessing seedling quality.