>Note: a number of materials such as the heavy metals, were once thought >to be "toxic" in an absolute sense. They are now considered, at least >by some, as being essential plant nutrients BUT IN VERY SMALL QUANTITIES.
In this vein, I would add that nutritional needs vary by species of plant as do
tolerances for nutrient excess. Some plants are bioaccumulators: that is,
they accumulate heavy metals at high concetrations in their tissues with no
adverse affect on the plant. There is a species of brake fern native to Florida
that is a hyperaccumulator for arsenic. Scientists are testing it for use in
soil clean up. What is interesting to me is that they find that it appears to
grow bigger and healthier in the presence of arsenic!
But arsenic is not a "vitamin". I have never heard that plants actually
*absorb* vitamins--I was under the impression that they are synthesized by the
plants themselves. I know soil contains minerals, micronutrients, phosphates,
nitrogen, and potassium salts, but vitamins? Maybe the original poster needs to
clarify whether she means vitamins or nutrients. There is a big difference.