This is an extract:

"the mechanisms of CO2 nutrient depletion may already be causing a decline in the quality of our
food supply. Josep Penuelas of the Centre for Ecological Research and Forestry Applications in
Barcelona, Spain, compared historical plant samples grown at preindustrial levels of atmospheric
CO2 with modern equivalents. He found that today's plants had the lowest levels of calcium,
copper, iron, potassium, magnesium, sodium, sulphur, and zinc than at any time in the last three
centuries."

The fill story is well woth reading:

http://www.grist.org/news/maindish/2005/07/12/scherer-plantchem/

Keith