Seasonal variations in monoterpene emissions from Eucalyptus species

Abstract

To understand the long-term and short-term variations in monoterpene emissions from Australian native trees and the factors which influence these variations, the seasonal variations in monoterpene emissions for 15 Eucalyptus species as well as the monthly and diurnal variations in monoterpene emissions for E. globulus were investigated using a dynamic flow chamber technique. Distinct seasonal variations both in chemical characteristics of monoterpene emissions and the monoterpene emission rates (normalised to 30°C) were characterised. The normalised monoterpene emission rates showed high emission rates during summer and low rates during other seasons for many Eucalyptus species. For example, the average normalised total monoterpene emission rate on a leaf mass basis (μg g⁻¹ h⁻¹) for E. globulus in summer was 5.4, 2.9 in autumn, 2.3 in spring and 1.5 in winter. The seasonal variation patterns appeared to be species-specific. The maximum values of monthly average total emission rates for E. globulus occurred in January (9.4 μg g⁻¹ h⁻¹ or 1.6 mg m⁻² h⁻¹), and the minimum values were in July (0.74 μg g⁻¹ h⁻¹ or 0.16 mg cm⁻² h⁻¹). The measured diurnal emission rates showed that there was a maximum emission rate at noon and two emission peaks at midnight and pre-dawn. Leaf temperature could be responsible for the diurnal variation in monoterpene emission rate under nonwetting leaf conditions. Temperature, light and relative humidity showed correlations with the variation in the average normalised monoterpene emission rate in E. globulus, but not with the variation in monoterpene emission composition. The variation in emission composition may be mainly controlled by the factors associated with leaf age. An algorithm for estimating monthly temperature-independent mean monoterpene emission rate from E. globulus was developed.