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Re: Mineral Nutrients
For all essential mineral nutrients, there is a concentration range in
which a small increase in a particular nutrient results in a large
increase in growth. This is the area of nutrient deficiency. At a
slightly higher concentration, there is a range in which a large increase
in concentration of a particular nutrient results in no noticeable
increase in growth at all. This is the area of nutrient sufficiency. In
this area, plants absorb and retain excess nutrients so that, though the
growth rate doesnt change, the amount of any particular nutrient within
the tissue increases dramatically. Finally, at the highest range, an
increase in a particular nutrient will produce a reduction in growth.
This is the area of nutrient toxicity.
If you see no change in growth when you add a particular nutrient such as
N or Fe, this means that you are in the area of nutrient sufficiency. If you
measured the content of N and Fe in the plant tissue, you would find
that they increase as you increase the external concentration.
Your result with CO2 is fascinating and underscores the importance of
inorganic carbon in controlling the growth of aquatic plants ... this
despite the fact that it is usually phosphorus that we try to limit in
aquaria. Next time you feel like experimenting, try increasing water
movement in the tank when you turn off the CO2 and see if the results are
as dramatic.
dave.