How does rising atmospheric CO2 affect marine organisms?

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Desiccation-Tolerant Plants and Elevated CO2
Tuba, Z., Csintalan, Z., Szente, K., Nagy, Z. and Grace, J.  1998.  Carbon gains by desiccation-tolerant plants at elevated CO2Functional Ecology 12: 39-44.

What was done
The authors rehydrated and regreened detached and desiccated leaves of Xerophyta scabrida(a woody shrub that grows in arid regions of east Africa) in air of 350 and 700 ppm CO2, after which they slowly desiccated them at the same CO2 concentrations within Plexiglas chambers to determine the effects of elevated CO2 on a typical poikilochlorophyllous desiccation-tolerant plant during desiccation.  In addition, two homoiochlorophyllous desiccation-tolerant plants --a moss and a lichen-- were grown in open-top chambers at 350 and 700 ppm atmospheric CO2 for five months, after which the effects of elevated CO2 on their desiccation processes were assessed.

What was learned
Elevated CO2 did not affect the amount of chlorophyll loss, the functioning of thylakoid membranes, or the time to complete drying during the desiccation of Xerophyta scabrida.  However, elevated CO2 allowed positive photosynthetic carbon gains in the leaves of this woody shrub to continue three times longer than it did in leaves exposed to ambient air.  This phenomenon resulted in the CO2-enriched leaves gaining more than ten times the amount of carbon from photosynthesis over the entire period of desiccation than was gained by the leaves exposed to normal air. 

Similar desiccation response patterns were observed in the moss and lichen grown at elevated CO2.  Positive photosynthetic carbon gains, for example, were maintained 14% longer with atmospheric CO2 enrichment; and total assimilation during the dry-down in elevated CO2 was increased by 52 and 69% for the lichen and moss, respectively.

What it means
As the CO2 content of the air continues to rise, desiccation-tolerant plants, of which there are many (18 genera of ferns, 23 genera of monocotyledons and 10 genera of dicotyledons), should be able to maintain positive rates of photosynthesis for a much longer duration than they do currently during times of desiccation.  The additional carbon gained at these times should lead to greater increases in biomass; and in some extreme cases, it may actually determine whether or not they survive a particularly long dry period.  Consequently, in the words of the authors, "desiccation-tolerant plants will be among the main beneficiaries of a high CO2 future."

Reviewed 15 December 1998