How does rising atmospheric CO2 affect marine organisms?

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CO2 and Plant Root Growth
Crookshanks, M., Taylor, G. and Dolan, L.  1998.  A model system to study the effects of elevated CO2 on the developmental physiology of roots: the use of Arabidopsis thalianaJournal of Experimental Botany 49: 593-597.

What was done
Seeds of the small, fast-growing Arabidopsis thaliana - the plant scientist's version of the medical "lab rat" - were sprouted on agar medium in Petri dishes and grown in controlled environment chambers maintained at atmospheric CO2 concentrations of either 355 or 700 ppm.  Visual assessments of root growth were made over a number of days following the emergence of the roots from the seeds.  Microscopic investigations of root cell properties were also conducted; and plants were periodically harvested to determine their total dry weight production.

What was learned
The CO2-enriched plants directed a greater proportion of their newly produced biomass into root, as opposed to shoot, growth.  In addition, they produced longer primary roots and more and longer lateral roots.  These effects were related to CO2 induced stimulation of mitotic activity, accelerated cortical cell expansion, and increased cell wall placticity.

What it means
The results of this study demonstrate that, even in a situation where nutrients are readily available to a plant and may thus be acquired with ease, atmospheric CO2 enrichment still enhances root growth, sometimes even more than it stimulates shoot growth.  In addition to the obvious benefits that enhanced water- and nutrient-collecting root systems provide for plants in real-world situations where water and nutrients may not be readily available, this finding suggests that more carbon than has previously been thought may be removed from the atmosphere and sequestered in the ground in a high CO2 world of the future.  This phenomenon, if demonstrated to be a common plant response to atmospheric CO2 enrichment, may in turn reduce the rate of rise of the air's CO2 content and thereby provide a natural "biospheric brake" upon the progression of potential CO2-induced global warming.

Reviewed 15 September 1998