How does rising atmospheric CO2 affect marine organisms?

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The Virtues of Thyme
Vurro, E, Bruni, R., Bianchi, A. and di Toppi, L.S. 2009. Elevated atmospheric CO2 decreases oxidative stress and increases essential oil yield in leaves of Thymus vulgaris grown in a mini-FACE system. Environmental and Experimental Botany 65: 99-106.

The authors write that thyme (Thymus vulgaris L.) has "a considerable economic value in the nutraceutical and pharmaceutical industry (Vardar-Uenlue et al., 2003; Konyalioglu et al., 2006)," and that "thyme essential oil possesses per se considerable antioxidant capacity (Economou et al., 1991), and may therefore contribute towards the control of antioxidant status in the leaves."

What was done
Vurro et al. grew well-watered one-year-old thyme plants for three additional months (10 June - 10 September) in pots (filled with 40% sand, 25% clay and 35% silt) out-of-doors within a mini-FACE (free-air CO2-enrichment) system at Ravenna, Italy, where the air's CO2 concentration was maintained at approximately 500 ppm (during daylight hours only), and where control plants were continuously exposed to air of approximately 370 ppm CO2, while they measured a number of plant parameters at the ends of each of the three months of the study.

What was learned
The four researchers report that "none of the plants grown under high levels of CO2 for 90 days presented either significant differences in fresh weight and dry weight compared with controls, or macroscopic alteration of morphogenesis (number and length of nodes/internodes, branching, leaf area and chlorosis, etc.), at any of the sampling times." However, they did find that "in plants grown under elevated CO2, a relative increase in oil yield of 32, 34 and 32% was, respectively, recorded in the first, second and third sampling-time (July, August and September)," and they observed a "general depression of the oxidative stress under elevated CO2" that led to a "down-regulation of leaf reactive oxygen species-scavenging enzymes under elevated CO2."

What it means
In the words of the Italian scientists, their results point to "a 'low cost' life strategy for growth under elevated CO2, not requiring synthesis/activation of energy-intensive and expensive metabolic processes," which thus allows the plants to invest more energy in the production of essential plant oils.

Economou, K.D., Oreopoulou, V. and Thomopoulos, C.D. 1991. Antioxidant activity of some plant extracts of the family Labiatae. Journal of the American Oil Chemists' Society 68: 109-113.

Konyalioglu, S., Ozturk, B. and Meral, G.E. 2006. Comparison of chemical compositions and antioxidant activities of the essential oils of two Ziziphora taxa from Anatolia. Pharmaceutical Biology 44: 121-126.

Vardar-Uenlue, G., Candan, F., Soekmen, A., Daferera, D., Polissiou, M., Soekmen, M., Doenmez, E. and Tepe, B. 2003. Antimicrobial and antioxidant activity of the essential oil and methanol extracts of Thymus pectinatus Fisch. et Mey var. pectinatus (Lamiaceae). Journal of Agricultural and Food Chemistry 51: 63-67.

Reviewed 22 April 2009