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Abstract
The emission of volatile organic compounds (VOCs) from plants has important effects on atmospheric chemistry and the carbon
dynamics on plants. Eucalypts are amongst the highest emitters of VOCs, yet there are relatively few studies of emissions from
this genus. The few studies published have examined emissions rates in relation to uncontrolled environmental variables. Only one study has examined these effects under controlled conditions. This thesis examined the factors that regulate VOC emissions
from Eucalyptus globulus, one of the most widely cultivated eucalypt species.
The emissions of isoprene, monoterpenes and the short-chained carbonyls formaldehyde, acetaldehyde and acetone were
determined from four eucalypt species. Carbonyl emissions were generally comparable with rates reported for other species.
There was large variation in diurnal isoprene and monoterpene emissions between species, but under standard conditions,
isoprene emissions were much lower than previous reports. Monoterpenes were as much as six times greater than previous
reports for some species. Emission of each carbonyl was correlated with its ambient concentration across different species.
The effects of temperature and light on isoprene and monoterpene emissions from E. globulus were studied under laboratory
conditions. Isoprene emissions exhibited the well described enzymatic response to increasing temperature, with a peak in
emission at around 45 °C. Monoterpenes exhibited a large transient burst in response to incremental increases in leaf temperature.
Analysis of the decay rate suggested a single pool contributed to the transient burst. I argue that emissions occur directly from oil
glands, regulated only by a thin layer of cap cells above the gland. Light-dependent emission of cis-ocimene was also observed.
Fumigation of leaves identified four compounds incorporated 13 C; isoprene (C5), cis-ocimene (C10), trans-caryophyllene (C15)
and the tentatively identified C5 compound iso-valeraldehyde. Emissions were only detected in emitted compounds and no
labelled uptake was identified in either oil glands or the remaining leaf tissue. The fraction of final 13C incorporation in the three
terpenoids appeared to match the established paths of biosynthesis.
Together, these data suggest that isoprene emissions from eucalypts may be a factor of two or more lower than previously
estimated, while the case for monoterpene emissions remains unclear.