Carl Strohmenger (
Sat, 4 Mar 1995 21:16:14 -0500 (EST)

It is probable that high concentrations of CO2 are poisonous to plants.
Plants in existence today, did not evolve in a high (5+%) concentration
of CO2. As with any nutrient, a little more is usually a good thing, but
often a *LOT* more is not so good. Have you ever tried to breathe a 100%
oxygen supply for more than a few minutes? It can do very bad things to
your lungs and other tissues. Plants are no different. Try enhancing the
CO2 up to 2% of the gas mixture. This level is probably OK.
- Carl