How does rising atmospheric CO2 affect marine organisms?

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Elevated CO2 and Phosphorus Uptake
Barrett, D.J., Richardson, A.E. and Gifford, R.M.  1998.  Elevated atmospheric CO2 concentrations increase wheat root phosphatase activity when growth is limited by phosphorus.  Australian Journal of Plant Physiology 25: 87-93.

What was done
Wheat seedlings were grown for 20 to 30 days in controlled environment cabinets at atmospheric CO2 concentrations of approximately 380 or 700 ppm.  In addition, transient or continuous phosphorus deficiency treatments were imposed on seedlings to determine if elevated CO2 would increase their phosphorus uptake under either of these regimes.  Furthermore, some seedlings were grown aseptically to determine if any CO2-meditaed increase in phosphorus uptake was plant-derived or microbial in origin.

What was learned
Elevated CO2 increased phosphatase activity in wheat roots grown under continuous, but not transient, phosphorous deficiency, with the largest percentage stimulation (30 to 40%) occurring in the most phosphorus deficient treatment.  As phosphatase is the primary enzyme responsible for the mineralization of organic phosphate, which thereby makes phosphorus available for plant use, an increase in its activity with elevated CO2 could facilitate sustained plant growth responses to elevated CO2 even in areas where growth is currently limited by phosphorous deficiencies.  Furthermore, because these increases in phosphatase activity were also observed under sterile growing conditions, this observation indicates that this response can be mediated directly by plant roots without involving soil microorganisms, which are already known to aid in phosphorus mineralization.

What it means
As the CO2 content of the air continues to rise, phosphatase activity in wheat roots should increase, thereby converting organic phosphorus into inorganic forms that can be used to support increased plant growth and development stimulated by higher CO2 concentrations.  Because a similar increase in phosphatase activity at elevated CO2 has already been reported for a native Australian pasture grass, these results may be applicable to most of earth's vegetation.  If this is the case, then plants that are currently phosphorus limited in their growth might increase their phosphorous acquisition from soil organic supplies as the atmospheric CO2 concentration increases.  This phenomenon, in turn, may allow them to sequester even greater amounts of carbon from the air as the present CO2 concentration climbs ever higher.

Reviewed 15 April 1999