Effects of soil water content and elevated CO concentration on the monoterpene emission rate of Cryptomeria japonica.

Monoterpenes emitted from plants contribute to the formation of secondary pollution and affect the climate system. Monoterpene emission rates may be affected by environmental changes such as increasing CO concentration caused by fossil fuel burning and drought stress induced by climate change. We measured monoterpene emissions from Cryptomeria japonica clone saplings grown under different CO concentrations (control: ambient CO level, elevated CO: 1000μmolmol). The saplings were planted in the ground and we did not artificially control the SWC. The relationship between the monoterpene emissions and naturally varying SWC was investigated. The dominant monoterpene was α-pinene, followed by sabinene. The monoterpene emission rates were exponentially correlated with temperature for all measurements and normalized (35°C) for each measurement day. The daily normalized monoterpene emission rates (E) were positively and linearly correlated with SWC under both control and elevated CO conditions (control: r=0.55, elevated CO: r=0.89). The slope of the regression line of E against SWC was significantly higher under elevated CO than under control conditions (ANCOVA: P<0.01), indicating that the effect of CO concentration on monoterpene emission rates differed by soil water status. The monoterpene emission rates estimated by considering temperature and SWC (Improved G93 algorithm) better agreed with the measured monoterpene emission rates, when compared with the emission rates estimated by considering temperature alone (G93 algorithm). Our results demonstrated that the combined effects of SWC and CO concentration are important for controlling the monoterpene emissions from C. japonica clone saplings. If these relationships can be applied to the other coniferous tree species, our results may be useful to improve accuracy of monoterpene emission estimates from the coniferous forests as affected by climate change in the present and foreseeable future.