Paper Reviewed
Mochizuki, T., Watanabe, M., Koike, T. and Tani, A. 2017. Monoterpene emissions from needles of hybrid larch F1 (Larix gmelinii var. japonica x Larix Kaempferi) grown under elevated carbon dioxide and ozone. Atmospheric Environment 148: 197-202.

Monoterpenes constitute a major fraction of the biogenic volatile organic compounds or BVOCs given off by plants. From a climatic perspective their emissions are important because they contribute to the formation of photochemical oxidants (e.g., ozone) and are thought by some to represent a positive feedback to global warming (Boucher et al., 2013).

Introducing their contribution to the subject, Mochizuki et al. (2017) write that "to estimate the effect of monoterpenes emitted from larch species on the atmospheric chemistry of the northeastern Eurasian continent in the present and foreseeable future, it is necessary to investigate how emissions and composition of monoterpenes emitted from larch species vary against climate change." Thus, the four Japanese researchers designed an experiment to investigate the effects of CO2 and ozone (O3), both alone and in combination, on monoterpene emissions from the hybrid larch F1 (Larix gmelinii var. japonica x Larix Kaempferi). More specifically, they grew 2-year-old seedlings in open-top chambers, subjecting them to control or elevated CO2 (380 ppm control, 600 ppm elevated) and/or O3 (<6 nmol mol^-1 control, 60 nmol mol^-1 elevated) concentrations during the daylight hours of two growing seasons, measuring their monoterpene emissions from 5-cm-long shoots.

So what did their experiment reveal?

Mochizuki et al. report that" total monoterpene emission rate decreased by 36% in response to elevated CO2 when compared with control (P < 0.05)." In the combined elevated CO2 x O3 treatment total monoterpene emissions also declined, and by nearly the same amount (32%), whereas it experienced a nonsignificant 23% increase in the elevated O3 treatment.

In light of the above findings, the negative effect of elevated CO2 on total monoterpene emissions observed in the saplings of the hybrid larch F1 should be welcomed by those concerned about future global warming for its potential to mitigate some of that warming.

Reference
Boucher, O., Randall, D., Artaxo, P., Bretherton, C., Feingold, G., Forster, P., Kerminen, V.M., Kondo, Y., Liao, H., Lohmann, U., Rasch, P., Satheesh, S.K., Sherwood, S., Stevens, B., Zhang, X.Y., 2013. Clouds and aerosols. In: Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex, V., Midgley, P.M. (Eds.), Climate Change 2013: the Physical Science Basis, Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.