Effects of Carbon Dioxide, Water Supply, and Seasonality on Terpene Content and Emission by Rosmarinus officinalis

Rosmarinus officinalis L. plants were grown under carbon dioxide concentrations of 350 and 700 μmol/mol (atmospheric CO2 and elevated CO2) and under two levels of irrigation (high water and low water) from October 1, 1994 to May 31, 1996. Elevated CO2 led to increasingly larger monthly growth rates than the atmospheric CO2 treatments. The increase was 9.5% in spring 1995, 23% in summer 1995, and 53% in spring 1996 in the high-water treatments, whereas in low-water treatments the growth response to elevated CO2 was constrained until the second year spring, when there was a 47% increase. The terpene concentration was slightly larger in the elevated CO2 treatments than in atmospheric CO2 treatments and reached a maximum 37% difference in spring 1996. There was no significant effect of water treatment, likely as a result of a mild low water treatment for a Mediterranean plant. Terpene concentration increased throughout the period of study, indicating possible age effects. The most abundant terpenes were α-pinene, cineole, camphor, borneol, and verbenone, which represented about 75% of the total. No significant differences were found in the terpene composition of the plants in the different treatments or seasons. The emission of volatile terpenes was much larger in spring (about 75 μg/dry wt/hr) than in autumn (about 10 μg/dry wt/hr), partly because of higher temperature and partly because of seasonal effect, but no significant difference was found because of CO2 or water treatment. The main terpene emitted was α-pinene, which represented about 50% of the total. There was no clear correlation between content and emission, either quantitatively or qualitatively. More volatile terpenes were proportionally more important in the total emission than in total content and in autumn than in spring.