How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

The Photosynthetic Adjustment of Mosses Exposed to Life-Long Atmospheric CO2 Enrichment
Csintalan, Z., Juhasz, A., Benko, Z., Raschi, A. and Tuba, Z.  2005.  Photosynthetic responses of forest-floor moss species to elevated CO2 level by a natural CO2 vent.  Cereal Research Communications 33: 177-180.

What was done
The authors note that long term growth in air of elevated CO2 concentration "may cause permanent biochemical, anatomical and phenological anomalies" in plants.  Hence, they decided to investigate this subject with cryptogam mosses and lichens growing in the vicinity of a natural CO2-emitting spring in the area of Lajatico (Toscana, Italy), where CO2 concentrations vary between 500 and 1000 ppm during daylight hours and average about 700 ppm over the daylight period, noting that these simple plants "with their rapid turnover and simple morphological characteristics could be one of the best indicators of global climate change."  Specifically, they measured the net CO2 assimilation rates of five well-hydrated forest-floor moss species growing in the vicinity of the CO2-emitting vent, but at a constant CO2 concentration of 350 ppm, in order to determine the nature of any photosynthetic acclimation that may have occurred in response to the plants' multi-generational exposure to an atmospheric CO2 concentration essentially twice that of the current atmosphere, comparing their results against results obtained from similarly-treated control plants growing outside the influence of the CO2 vent.

What was learned
Quoting the Hungarian and Italian researchers, "the CO2 assimilation was higher in the native CO2 vent species."  Reading as best we can from the bar graph of their results, the net CO2 assimilation rates of the plants that had been exposed to a nominally-doubled atmospheric CO2 concentration for their entire lives (but that were measured at a CO2 concentration of 350 ppm), net CO2 assimilation rate was 42% greater for Ctenidium molluscum (Hedw.) Mitt., Hypnaceae Fleisch., 44% greater for Hypnum cupressiforme (Hedw.), Hypnaceae Fleisch., 49% greater for Pseudoscleropodium purum (Hedw.), Brachytheciaceae B.S.G., 80% greater for Pleurochaete squarrosa (Brid.) Lindb., Trichostomaceae B.S.G., and 85% greater for Platygyrium repens (Brid.), B.S.G., Hypnaceae Fleisch.

What it means
Contrary to the results of many shorter-term elevated-CO2-exposure experiments (see Acclimation in our Subject Index), where downward (but typically not complete) acclimation of photosynthesis has been observed, Csintalan et al. were able to report that "native mosses showed upward acclimation," indicative of an extremely positive long-term photosynthetic adjustment of the five species to life-long (indeed, multi-generational) atmospheric CO2 enrichment.

Reviewed 13 July 2005