BIOLOGIA PLANTARUM 53 (2): 351-354, 2009
Increase in isoprene and monoterpene emissions after re-watering
of droughted Quercus ilex seedlings
J. PEÑUELAS*, I. FILELLA, R. SECO and J. LLUSIÀ
Unitat d’Ecofisiologia i Canvi Global CSIC-CEAB-CREAF, Universitat Autònoma de Barcelona,
E-08193 Bellaterra, Barcelona, Spain
We followed the diurnal cycles of isoprenoid emissions from Quercus ilex seedlings under drought and after re-
watering. We found that Quercus ilex, generally considered a non-isoprene emitter, also emitted isoprene although at
low rates. The emission rates of isoprene reached 0.37 ± 0.02 nmol m-2 s-1 in controls, 0.15 ± 0.03 nmol m-2 s-1 under
drought and 0.35 ± 0.04 nmol m-2 s-1 after re-watering, while emission rates of monoterpenes reached 11.0 ± 3.0,
7.0 ± 1.0 and 23.0 ± 5.0 nmol m-2 s-1, respectively. Emission rates recovered faster after re-watering than photosynthetic
rate and followed diurnal changes in irradiance in controls and under drought, but in leaf temperature after re-watering.
Additional key words: light-dependent emissions, net photosynthetic rate, PTR-MS, stomatal conductance, temperature-dependent
Plant volatile organic compounds (VOCs) include
isoprene, terpenes, alkanes, alkenes, alcohols, esters,
carbonyls and acids (Peñuelas and Llusià 2003). VOCs
have many protective and ecological functions for the
plant species that produce them and have important
effects on the photochemistry and radiative properties of
the atmosphere (Zimmerman et al. 1978, Kavouras et al.
1998, Peñuelas and Llusià 2003, Owen and Peñuelas
2005). Consequently there is great interest in determining
the emission capacities of the different species and how
environmental factors affect the volatile isoprenoid
emissions (Peñuelas and Llusià 2001).
Oaks belong to the greatest VOC emitters (Harley
et al. 1999). The holm oak (Quercus ilex L.), a widely
distributed species in the Mediterranean basin, is
considered a monoterpene and non-isoprene emitter
(Kesselmeier and Staudt 1999, Loreto 2002) although
Owen et al. (1997) reported small emission rates of
isoprene. Variations in the emission of volatiles can also
be triggered by changing environmental conditions
(Peñuelas and Llusià 1999a, 2001, Niinemets et al. 2004).
Received 8 September 2007, accepted 20 January 2008.
Abbreviations: VOCs - volatile organic compounds; PTR-MS - proton-transfer-reaction mass spectrometer, PN - net photosynthetic
rate; gs - stomatal conductance.
Acknowledgements: This research was partially supported by Spanish MCYT grants CSD2008-00040 Consolider-Montes and
CGL-2006-04025/BOS, the European Commission RTN “ISONET” contract MC-RTN-CT-2003-504720, the European Science
Foundation “VOCBAS” program and a Catalan government SGR2005-00312 grant. Roger Seco gratefully acknowledges a FPI
fellowship (BES-2005-6989) from MEC (Spanish Government).
* Corresponding author; fax: (+34) 93 5814151, e-mail: firstname.lastname@example.org
No specialized storage structures for monoterpenes have
been found in its leaves or bark, and emissions appear to
be mainly influenced by temperature, irradiance and
water availability (Loreto et al. 1998, Llusià and Peñuelas
1998, 1999, 2000, Peñuelas and Llusià 1999a,b, Staudt
et al. 2002).
In Mediterranean areas, drought driven changes in
emission may be even more relevant under the future
climate, since water availability in the Mediterranean
region is likely to be reduced in the near future by the
predicted increases in temperature and the consequent
increases in evapotranspiration rates (Sabaté et al. 2002,
Peñuelas et al. 2005). These changes in emissions may
have important consequences in the formation of photo-
chemical pollutants in this Mediterranean area (Filella
and Peñuelas 2006).
The aim of this study was to describe the changes in
isoprenoid emission rates induced by drought conditions
and after subsequent re-watering together with physiolo-
gical variables such as CO2 and water exchange.
J. PEÑUELAS et al.
a nursery (Forestal Catalana, S.A., Breda, Spain) under
typical Mediterranean environmental conditions (mean
annual average temperature 16 ºC and mean annual
precipitation 600 mm). They were grown in 2-dm3 pots
with a substrate composed of peat and sand (2:1), prior to
being brought into the laboratory, where they were kept
some days for an acclimation before starting the
experiment. Control (well watered) plants were measured
over one day at soil moisture of 25 % (volume of water
per volume of dry soil; v/v), measured by time domain
reflectometry (Tektronix 1502C, Beaverton, Oregon,
USA) and left un-watered until soil water content reached
5 %. After one new day of measurements under these
drought conditions, plants were re-watered until soil
water content reached 25 % and measured again over
another day. Three replicates were conducted, all at room
temperature (25 ºC).
Intact leaves were clamped in a Parkinson leaf cuvette
(Std Broad 2.5, PP Systems, Hitchin, England). The air
entering the system was sampled at 4 m above ground
from the outside of the building, filtered with glass wool
to prevent any dust intake and passed through a
polyethylene terephthalate (PET) recipient to buffer
exterior CO2 and VOC fluctuations. All tubing used was
made of inert polytetrafluoroethylene (PTFE). A diurnal
cycle of irradiance was programmed to simulate a typical
sunny day, photosynthetic photon flux density (PPFD)
ranging from 0 to 1500 µmol m-2 s-1. The leaf temperature
ranged between 25 and 32º C. A calibrated Ciras-2
IRGA-porometer (PP Systems) was used for determining
rates of CO2 and H2O exchange. Part of the air exiting the
leaf cuvette flowed through a T-system to the PTR inlet.
We used a highly sensitive proton-transfer-reaction
mass spectrometer (PTR-MS-FTD, Ionicon Analytik,
Innsbruck, Austria) as described by Lindinger et al.
(1998). The PTR-MS drift tube was operated at 0.21 kPa
and 40 ºC, with a drift field of 600 V cm-1. The parent ion
signal was maintained at around 3 × 106 counts s-1 during
the measurements. We measured isoprene (m69) and
monoterpenes (m137). The quantification of isoprene and
monoterpenes was based on the use of 3 times replicated
calibration standards of isoprene and α-pinene (Sigma-
Aldrich, Barcelona, Spain).
For volatile isoprenoid determination and quanti-
fication, both the air entering and exiting the leaf cuvette
were analysed by (PTR-MS), at alternate 5-min intervals,
and continuously monitored with flow meters. The
difference between the concentration of volatile
isoprenoids before and after passing through the cuvette
(with leaves and without leaves), along with the flow
rates, was used to calculate the volatile isoprenoid
exchange (Peñuelas et al. 2007). Leaves were excised
after emission sampling to measure leaf area (LI 3100,
leaf area meter, Li-Cor, Lincoln, NE, USA). Leaves were
then dried in an oven at 70 °C until constant weight
(usually for 72 h) to determine dry mass.
We used one way ANOVA, and Bonferroni post-hoc
tests to compare the leaf emissions in the three different
We used two-year-old Quercus ilex L. plants grown in
treatments. Regression and correlation analyses were also
conducted for the studied variables. In all cases we used
Statistica (Statsoft Inc., Tulsa, OK, USA) programme
Q. ilex seedlings emitted isoprene in all three
replicates both under control watered conditions and in
the three replicate measurements of the diurnal cycle
during drought/re-watering experiment (Fig. 1 shows one
of those replicates). The emission rates of isoprene
reached 0.37 ± 0.02 nmol m-2 s-1 in control conditions,
0.15 ± 0.03 nmol m-2 s-1 in drought conditions and 0.35 ±
0.04 nmol m-2 s-1 in re-watering conditions (significantly
different at, P < 0.01, n = 3). Those of monoterpenes
reached 11.0 ± 3.0, 7.0 ± 1.0, and 23.0 ± 5.0 nmol m-2 s-1,
respectively. Q. ilex was thus emitting low but significant
amounts of isoprene, and the emissions ranged between
1.5 and 3.4 % of monoterpene emissions. These
emissions of isoprene were slightly higher than those
reported in the previous study (Owen et al. 1997).
There was a clear diurnal cycle in emissions of both
isoprene and monoterpenes. Both emissions were
stimulated during day and declined in the dark. As in
recent physiological studies of oaks (Schnitzler et al.
2004) these isoprenoid emissions by Q. ilex were largely
associated to net photosynthetic rate (PN) and stomatal
conductance (gs) which presented two peaks, one in the
morning and another one in the afternoon when
irradiance and temperature started to decrease (Fig. 1).
The concurrently performed
photosynthesis revealed that Q. ilex leaves lost about 0.7 -
1.5 ‰ of the assimilated carbon via isoprenoid emission;
lower than reported under field conditions in several
other studies (Sharkey and Loreto 1993, Kesselmeier and
Staudt 1999, Peñuelas and Llusià 1999a,b, 2001, Llusià
and Peñuelas 2000).
The relative water content of Q. ilex leaves in the
control, drought and re-watering treatments were 93.0 ±
2.2, 77.1 ± 4.0 and 91.8 ± 0.3 %, respectively (signifi-
cantly different, P < 0.01). The early morning values of
PN and gs were high even under drought since these plants
take advantage of a short window of activity in the
mornings after the night water status recovery. PN and gs
in the afternoon followed the changes in water
availability rapidly; they increased by more than twice
the day after re-watering (Fig. 1). The emissions of
isoprene and monoterpenes increased even more, ca.
3 times, after re-watering the droughted plants (Fig. 1).
They responded immediately to changes in leaf
temperature but not to changes in PN or gs as occurred in
controls and under drought. This is another manifestation
of the uncoupling between volatile isoprenoid emissions
and photosynthesis described in several previous studies
that showed that short term drought caused substantial
reduction in photosynthesis, whereas isoprene emissions
were either not inhibited or only slightly reduced (Tingey
et al. 1981, Sharkey and Loreto 1993, Fang et al. 1996,
Funk et al. 2005). The changes in the emissions’
dependence on temperature after re-watering (Fig. 1)
indicated that the temperature was the factor driving
ISOPRENE AND MONOTERPENE EMISSIONS
increases in the emission rates, probably as a result of
enhanced isoprenoid synthesis, diffusivity and volatility
(Peñuelas and Llusià 2001). Our results also indicate that
emissions recovered to previous unstressed values faster
than PN or gs which is in agreement with the recent results
reported for isoprene emissions in Populus alba by Brilli
et al. (2007). In addition, our results show very high
terpene emission rates just after the re-watering of plants.
During the recovery, the emission rates reached values in
the higher limit or above the normal range reported for
this species in this Mediterranean region (Llusià and
Peñuelas 2000, Peñuelas et al. 2007). Further studies are
necessary to figure out the mechanisms ruling this high
emission rates temporally uncoupled of photosynthesis
and highly responsive to temperature.
Although the extrapolation of these results to field
conditions is never straightforward, they show that Q. ilex
is able to emit isoprene and that there are complex
responses of isoprene and monoterpene emissions to
drought cycles. The emission of volatile organic
compounds from vegetation is particularly sensitive to
temperature (e.g. Peñuelas and Llusià 2001, 2003,
Guenther et al. 1995, Filella et al. 2007), but the effects
of drought that accompany high temperatures must also
be considered to estimate the consequences of climate
change on isoprenoid emissions, especially because of the
Fig. 1. Daily time course dynamics of PFD, leaf temperature, net photosynthetic rates, stomatal conductance and isoprene and
monoterpene emissions in a Quercus ilex potted seedling submitted to drought and re-watering. Vertical line indicates the moment of
re-watering. Replicated three times (see text).
J. PEÑUELAS et al. Download full-text
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