How does rising atmospheric CO2 affect marine organisms?

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Stomatal Responses of Temperate Woodland Plants to Elevated CO2
Beerling, D.J. and Kelly, C.K.  1997.  Stomatal density responses of temperate woodland plants over the past seven decades of CO2 increase: A comparison of Salisbury (1927) with contemporary data.  American Journal of Botany 84: 1572-1583.

What was done
Stomatal densities of 60 tree, shrub, and herb species from temperate woodlands located within the United Kingdom were examined and compared with similar data recorded by Salisbury in 1927 to determine if the rising CO2 content of the air over the past 70 years has influenced this leaf characteristic.

What was learned
Over the past seven decades, the rising CO2 content of the air caused a significant decrease in the stomatal densities of woodland species growing in the United Kingdom.  This response was found to be independent of plant form but dependent upon initial leaf stomatal density, with species that historically had higher densities exhibiting greater current density reductions than species that historically had relatively lower stomatal densities.

What it means
Over the past seven decades, the rising CO2 content of the air caused a significant reduction in the stomatal densities of 60 temperate woodland species.  Consequently, this phenomenon likely lowered stomatal conductance and transpirational water loss, which likely contributed to an increase in plant water-use efficiency over this period.  As the atmospheric CO2 concentration continues to rise, it is therefore likely that stomatal densities will continue to drop, thereby facilitating even greater reductions in transpirational water loss, which phenomenon can provide a biological impetus for expanding vegetation within arid and semi-arid desert regions.

Reviewed 15 September 1999