1. Introduction
In recent years there has been a growing inter- est for introducing so-called alternative crops in
Europe. One such crop is quinoa Chenopodium
quinoa Willd originating from the South Ameri- can highlands, where it has been cultivated by
local farmers for several millennia. The Andes region is characterised by a harsh climate, with
frequent periods of drought, imposing great de- mands on the local flora, and quinoa is therefore
considered a hardy plant with good drought toler- ance Galwey, 1989; Jacobsen, 1993; Jacobsen et
al., 1997a,b, 1998. Previously, several investiga- tions have shown that quinoa is drought tolerant
which has been attributed to morphological char- acteristics such as an extensive ramified root sys-
tem and hygroscopic papillae on the leaf cuticula Canahua, 1977; Espindola, 1986 but data on
physiological response to drought are scarce Vacher, 1998. However, until now few investiga-
tions have been undertaken in order to study the leaf water relations of quinoa in the field and
during the season.
Turgor maintenance during reduction in leaf water status due to drought was thought to be the
means by which a plant maintains its metabolic processes and sustains its growth and survival
e.g. Hsiao et al., 1986; McCree, 1986. Turgor maintenance may be obtained by a sensitive stom-
ata closure response induced by phytohormones generated in the roots Jensen et al., 1998; Ali et
al., 1999, osmotic adjustment Ali et al., 1999 or facilitated by changes in cell wall properties Cut-
ler et al., 1977. Under limited water conditions, higher yield was obtained by wheat genotypes
having high osmotic adjustment than low osmotic adjustment Morgan et al., 1986. Furthermore,
inherent low osmotic potentials will be a mean by which the plants can sustain a potential gradient
for water uptake when the soil water potential is decreased during soil drying Jensen et al., 1993;
Shalhevet, 1993. Finally, high photosynthetic rates and specific leaf area SLA support early
vigour important to drought resistance to a fol- lowing long lasting drought period in Mediter-
ranean-type climate by reducing the amount of water lost by soil evaporation Turner, 1997.
As gas exchange and water relations have not been studied in field quinoa as far as we know,
the purpose of the present investigation was to study the effects of drought on leaf conductance,
net photosynthesis and leaf water relations char- acteristics during drought at different stages of
growth in field grown plants. Gas exchange and water relations characteristics of quinoa were
compared with various cultivated crop species.
2. Materials and methods
A pot and a lysimeter experiment was con- ducted in the field at the experimental station
Højbakkegaard of the Agricultural University, KVL, 20 km west of Copenhagen 55°40 N;
12°18 E; 28 m above MSL. A mobile glass roof automatically protected pots and lysimeter plots
against rain. When rain ceased the roof was re- moved automatically.
2
.
1
. Pot experiment The quinoa variety Chenopodium quinoa Willd.
cv. Kankolla was sown on 20 May 1997, in pots and germinated 1 June 1997. Kankolla is a tradi-
tionally grown variety of the Peruvian altiplano with a high level of drought and frost tolerance.
The pots were fertilised with 3 g N, 1 g P and 3 g K per pot mixed into the soil. The pots contained
a sandy soil a coarse textured melt-water top sand from the Danish Governmental Research
Station, Jyndevad with a water content of 19 vol. at field capacity − 0.01 MPa and 5 vol.
at permanent wilting − 1.5 MPa. The soil water retention curve is shown in Fig. 1. Forty pots
were used and each contained 21.6 kg of dry soil comprising 3.4 organic matter, 4.2 clay 0 – 2
mm, 3.8 silt 2 – 20 mm, 10 fine sand 20 – 200 mm and 78.7 coarse sand 200 – 2000 mm. The
pots had a diameter of 20 cm and a height of 40 cm. Two plants were grown in each pot. Four
pots per treatment was used for final yield deter- mination after drying at 80°C for 24 h. Drought
was imposed during branching eight true leaves stage 0, flowering stage 8 – 12 and grain filling
stage 14 – 18; according to Jacobsen and Stølen,
1993 by withholding watering. The drought treat- ment was undertaken under moderate evaporative
demands Fig. 2.
2
.
2
. Lysimeter experiment Quinoa Chenopodium quinoa Willd. cv. KVL
205 sown on 20 May 1994 and emerged on 3 June 1994, was grown under temperate climatic
conditions Fig. 2. Seeds were sown at a density of 30 grains m
− 1
with a row spacing of 12.5 cm, i.e. 400 seeds m
− 2
. Prior to sowing 120, 30, 90 and 9 kg ha
− 1
of N, P, K and Mg, respectively, was applied. The experiment was established in 12
lysimeter plots each 2 × 2 m
2
area on sandy loam Kristensen and Aslyng, 1971. At the bor-
der of each lysimeter plot the protection areas were treated the same as the lysimeter plots. The
sandy loam contained 3 organic matter, 16 clay 0 – 2 mm, 17 silt 2 – 20 mm, 40 fine sand
20 – 200 mm and 24 coarse sand 200 – 2000 mm in the top soil 0 – 30 cm depth and 20 clay,
17 silt, 43 fine sand and 20 coarse sand in the bottom layer 30 – 100 cm depth. The water
content in this soil is 260 mm at field capacity − 0.01 MPa and 115 mm at permanent wilting
− 1.5 MPa, giving the plant available soil water of 145 mm. The soil water retention curve is seen
in Fig. 1.
Each lysimeter plot was supplied with an indi- vidually operated trickle irrigation system. Six
plots were well-watered and six were equally treated with a single drought treatment and sub-
jected to increasing soil water deficits at the late anthesisearly grain filling stage 12 – 14 according
to Jacobsen and Stølen, 1993. The drought treat- ment was undertaken under moderate evaporative
demands Fig. 2.
2
.
3
. Plant water relations Leaf water relation measurements were made
during 4 h centred around solar noon. The leaf was enclosed in a polyethylene bag after gas ex-
change measurement in the field, and immediately detached for measurement of its water potential
c
l
using a pressure chamber Soil Moisture Equipment, Santa Barbara, CA. After taking the
water potential measurement, the leaf was divided into two parts, one of which was immediately
plunged into liquid nitrogen and then transferred to a freezer of − 20°C for later osmotic potential
determination. The second half of the leaf was used for relative water content determination
[RWC = FW − DWTW − DW]. To this end the leaf sample was weighted FW and then
floated on distilled water for 4 h at 22°C under dim light. The turgid weight TW was determined
after blotting, and the dry weight DW was mea- sured after the samples had been dried for 24 h at
80°C. The one-sided area was measured by a leaf area meter model 3050A, LiCor Inc. Lincoln
NE. Specific leaf area SLA was calculated as leaf area per unit of dry mass.
To determine the osmotic potential, the frozen leaf was allowed to thaw for about 20 min before
being pressed. Then the press sap was removed with a filter paper disc and sealed in a C-52
chamber Wescor Inc. Logan, UT and incubated at 22°C for 10 – 15 min before osmotic potential
Fig. 1. Soil – water characteristic curve in sand Hansen and Jensen, 1986 pot experiment and loam lysimeter experi-
ment. In sand bars indicate 9 S.E.M. n = 24.
Fig. 2. Mean daily values of relative humidity a, air temperature b, irradiance c, and potential evapotranspiration as calculated by the equation of Penman 1956. · · · · · 1994 lysimeter experiment. - - - - 1997 pot experiment.
was read with a dew point microvoltmeter HR – 33T, Wescor Inc., Logan, UT, USA. Leaf turgor
potential c
p
was obtained as: c
p
= c
l
− c
p
. The osmotic potential at full hydration c
p 100
was calculated as: c
p 100
= c
p
× RWC.
Water retention characteristics of leaves were assessed using pressure – volume PV curves ob-
tained with a pressure chamber at the end of the drying period of the lysimeter experiment. Fully
expanded upper leaves selected from the gross boundary layer of the crop were excised in dis-
tilled water at dawn and rehydrated for 3 – 4 h in sealed glass in the dark. Drying of the leaves
between c
l
measurements took place on the bench, and changes in leaf water contents were
determined by weighing immediately after the c
l
determination with six replicates for every treat- ment. Each leaf was partially wrapped in a plastic
sheet in order to decrease the rate of drying. Data for one PV-curve of each single leaf were obtained
within 12 h.
By plotting 1c
l
versus RWC type II transfor- mation a curve was obtained with an initially
non-linear portion followed by and approximately linear section. The beginning of the linear portion
indicates the leaf water potential at the turgor loss point c
leaf
and the RWC value at zero turgor RWC
. Data points belonging to the turgor and zero turgor region were discriminated by eye. The
bulk elastic volumetric modulus o was defined as:
o = V dc
p
dV which is the change in turgor pressure dc
p
for an infinitesimal change in symplastic water con-
tent V Andersen et al., 1991. When RWC = 1 then =
max
. It was assumed that the relation- ship between c
p
and 1RWC
s
, where RWC
s
is relative symplastic water content, can be de-
scribed by an exponential function. Hereby, at RWC
s
= 1 − RWC
a
, where RWC
a
is the relative apoplastic water content, the maximum turgor
c
pmax
is reached. The derivation of RWC
a
is given by Andersen et al. 1991. Turgor in the
turgid region was described as: c
p
= c
pmax
e
b [RWC
s −
1
− 1 − RWC
a −
1
]
where b, the sensitivity factor of elasticity, relates exponential changes in turgor to changes in
RWC
s
Andersen et al., 1991.
2
.
4
. Gas exchange measurement Leaf conductance g
l
and photosynthesis A were measured in 10 – 15 days old fully expanded
upper leaves on attached leaves using the LI-6200 portable photosynthesis system LiCor, Lincoln,
NE and a 250 ml cuvette. The leaves were posi- tioned within the gross boundary layer of the
crop. Inside the cuvette the photosynthetic active radiation PAR, 400 – 700 nm was 87 of that
outside. Only light saturated photosynthesis at PAR \ 800 mmol m
− 2
s
− 1
was used. Leaf tem- perature varied between 27 and 33°C. Relative
humidity in the cuvette was 35 – 45. [CO
2
] in the cuvette was between 320 and 340 ppm. The gas
exchange measurement was undertaken about 0.5 min after the leaf had been inserted into the
cuvette. The standard calibration check was per- formed by the manufacturer before and after the
growing season. No drift had occurred in the water vapour and CO
2
calibration curves. As a daily routine a CO
2
calibration check was per- formed on the instrument. The boundary layer
conductance in the cuvette as measured on leaf- shaped humidified filter paper was 3.0 mol m
− 2
s
− 1
.
2
.
5
. Nitrogen The total nitrogen content in the dry matter
was measured by the Kjeldahl method Bremmer and Mulvaney, 1982.
2
.
6
. Statistics The experiment was arranged in a systematic
block design with four to six replicates of each treatment. Student t-test was used to determine if
the means of the two treatments were different SAS, 1988.
3. Results
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