AbstractThis study has combined laboratory and greenhouse based experiments using sitka-spruce seedlings, with field studies to examine the effects by heavy metals upon tree growth.
Water culture techniques were used to determine the upper critical tissue concentrations for cadmium, copper, lead, nickel and zinc ions: these being the lowest concentrations at which shoot yields were affected. Concentrations of these heavy metals in the soil and foliage at the South Wales forestry sites were found to be elevated with respect to a control site in Mid Wales (Tywi). A comparison of these foliar levels with the critical tissue concentrations showed several sites to be at risk to nickel toxicity (Burton et al 1983).
The interactive effects of heavy metals, studied by means of factorial experiments in water culture, did not reveal any synergistic or antagonistic reductions in the yields of the seedlings. However, the interactive effects of these metals were found, in some cases to be additive. Several sites had foliar levels of cadmium and lead which approached their upper critical tissue concentrations. The effects upon tree growth may be even greater at these sites. These experiments also showed that heavy metals can influence the uptake into the shoots and roots of other heavy metals and nutrients.
The field situations were more closely modelled using greenhouse experiments with seedlings grown in a typical forestry soil with added heavy metals. Effects upon the growth of the seedlings, as measured by yields of shoots and roots and root lengths, were demonstrated. At soil concentrations of cadmium and lead which were similar to those found at the forestry sites, there were disturbances in the root-mycorrhizal associations indicating that tree growth may also be indirectly affected by the heavy metals in the soil.
|Date of Award||Jun 1993|