>On Tue, 2 Aug 2005 23:07, Thomas Bridgeland wrote:
>
>>On Tuesday, August 2, 2005, at 08:09  PM, Keith Thomas wrote:
>>> ...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."
>>
>>This may just be a fertilization effect. CO2 is a plant nutrient. When
>>the level is high, plants grow faster and so other nutrient levels are
>>lower. Same thing is true if you use lots of N. Anything that speeds
>>plant growth will have this effect.

I received the following comment on The Scherer paper:

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

and thought I should post it here to round out the discussion:
-----------------------------------------
The Scherer paper shows the risk of drawing false conclusions
from looking at a single factor rather than systems ecologies.
Sure under non-limiting glasshouse conditions plants can fix
more carbon as as CO2 goes up making plants grow faster and
bigger. Similarly, as nutrient uptake does not increase
correspondingly the nutrient concentrations and food
value of these products declines.

However what they ignore is that in the
field, CO2 concentrations rarely limit plant growth.
Although water availability and temperature can limit
growth it is the availability of essential nutrients
(as distinct from their levels in soil) that most
dramatically limit plant growth. Availabilities are
substantially governed by microbial processes.
Consequently the effects of climate change on these
processes will be the key determinant on plant growth
rather than any increased CO2 levels. Temperature has
a major effect on the microbiology of both nutrient
cycling and disease organisms which need to be defined
on a case by case basis. So don't put your money on
expecting bumper crops in response to climate change.
-------------------------------------
Keith