Revista Chilena de Historia Natural 75 (3): 603-612, 2002
RESEARCH ARTICLE
Importance of the chemical form and type of substrate for copper toxicity in Noticastrum
sericeum (Less.) Less. ex Phil.
The increase of copper concentration in soils due to human activities may result in plant
toxicity, particularly in sensitive species. However, it has been postulated that some edaphic factors may determine the bioavailable
copper fraction in soils and thus the intensity of fitotoxicity, such as the physicochemistry of the substrate, besides the intrinsic
solubility of the chemical form in which copper is incorporated to soil. To determine the importance of the metal buffering capacity of
the plant-growth substrate and the copper form on the intensity of copper toxicity, seedlings of a sensitive plant species were exposed
to increasing copper concentrations, added as a high water soluble form (CuSO<sub>4</sub>) or as a low water soluble
form (CuO) to substrates with high (commercial compost, high content of organic matter and neutral pH) and low (solution of 2 mmol
L<sup>-1</sup> calcium nitrate with no organic matter and slightly acidic pH) copper buffering capacity. Significant effects of
copper toxicity were found in roots of seedlings grown in solutions spiked with either CuSO<sub>4</sub> or CuO, at both
experimental concentrations, as growth of primary roots was inhibited and the number of secondary roots was reduced. Shoots
showed less effects of toxicity as expected, but a significant reduction in the number of leaves was detected on seedlings grown in
solutions spiked with CuSO4, at both concentrations, and with high concentration of CuO. No toxicity effects were detected on
seedlings grown in commercial compost spiked either with copper sulphate or copper oxide, at any experimental concentration,
because the high buffering capacity of the organic matter and the neutral pH of the substrate resulted in low availability of copper ions
for plant uptake. Therefore, plant response to elevated copper concentrations is multifactorial and cannot be only assessed from the
total copper levels added to soils.
Key words:
bioavailability,
fitotoxicity, soil pollution, metals
