A comparison of carbon and water vapor gas exchange characteristics between a diploid and highbush blueberry


Moon, J.W.; Flore, J.A.; Hancock, J.F.

Journal of the American Society for Horticultural Science 112(1): 134-138

1987


CO2 assimilation (A), leaf conductance to water vapor (g1), mesophyll conductance (gm), and water use efficiency (WUE) were compared for two cultivars of highbush (Vaccinium corymbosum L.) and a wild diploid lowbush blueberry species (Vaccinium darrowii Camp.) in response to PPF, CO2, temperature, and vapor prssure deficit (VPD) to determine if apparent tolerance of V. darrowii to high temperature and drought conditions resulted from differences in gas exchange characteristics. Cultivars differences between 'Bluecrop' and 'Jersey' in A were not significant when expressed on a leaf area, leaf dry weight, or total chlorophyll basis. Maximum CO2 assimilation rates for V. darrowii were about 35%, 50%, or 40% lower than highbush cultivars when expressed on a leaf area, leaf dry weight, or total chlorophyll basis, respectively. Differences between 'Bluecrop' and 'Jersey' were also non-significant for mesophyll conductance, transpiration, CO2 compensation points, and water use efficiency. CO2 assimilation maximized between 600-800 .mu.mol .cntdot. s-1 .cntdot. m-2 photosynthetic photon flux (PPF) for all three genotypes and the temperature optima ranged between 18.degree. and 26.degree. C for 'Jersey', 14.degree. and 22.degree. for 'Bluecrop', and 25.degree. and 30.degree. for V. darrowii. As temperature was increased from 20.degree. to 30.degree., leaf conductance (g1) to water vapor was lower and water use efficiency was higher for V. darrowii, compared to 'Bluecrop' but not 'Jersey'. There was a 50-65% reduction in g1 as VPD was increased, but only 10-20% reduction was observed in A. Leaf conductance to water vapor was reduced for V. darrowii, which restricted intercellular CO2. Since crosses are possible between highbush and V. darrowii, it is possible that heat tolerance and/or drought resistance could be improved in Highbush blueberry through the incorporation of genes from V. darrowii.

of
intercellular
spaces
in
plant
tissues.
Acta
Soc.
Bot.
Pol.
33:247-
262.
10.
Czerski,
J.
1968.
Gasometric
method
of
water
deficit
measure-
ment
in
leaves.
Biol.
Plant.
10:275-283.
11.
Eaks,
I.L.
and
W.A.
Ludi.
1960.
Effects
of
temperature,
wash-
ing,
and
waxing
on
the
composition
of
the
internal
atmosphere
of
orange
fruits.
Proc.
Amer.
Soc.
Hort.
Sci.
76:220-228.
12.
Smith,
W.H.
1947.
A
new
method
for
the
determination
of
t
h
e
composition
of
the
internal
atmosphere
of
fleshy
plant
o
rgans.
Ann.
Bot.
11:363-368.
13.
Spector,
W.S.
1956.
Handbook
of
biological
data.
Tech,
R
pt,
Wright
Air
Development
Center,
No.
56-273.
14.
Vaz,
R.L.
1982.
Factors
influencing
gas
exchange
characteristic%
of
fruits.
MS
Thesis,
Univ.
of
California,
Davis.
J.
AMER.
SOC.
HORT.
Sci.
112(1):134-138.
1987.
A
Comparison
of
Carbon
and
Water
Vapor
Gas
Exchange
Characteristics
Between
a
Diploid
and
Highbush
Blueberry
J.W.
Moon,
Jr.',
J.A.
Fiore,
and
J.F.
Hancock,
Jr.
Department
of
Horticulture,
Michigan
State
University,
East
Lansing,
MI
48824
Additional
index
words.
residual
conductance,
CO
2
compensation
point,
light
saturation Vaccinium
darrowii,
Vaccinium
corymbosum
Abstract.
CO
2
assimilation
(A),
leaf
conductance
to
water
vapor
(g
1
),
mesophyll
conductance
(g
m
),
and
water
use
efficiency
(WUE)
were
compared
for
two
cultivars
of
highbush
(Vaccinium
corymbosum
L.)
and
a
wild
diploid
lowbush
blueberry
species
(Vaccinium
darrowii
Camp.)
in
response
to
PPF,
CO
2
,
temperature,
and
vapor
pressure
deficit
(VPD)
to
determine
if
apparent
tolerance
of
V.
darrowii
to
high
temperature
and
drought
conditions
resulted
from
differences
in
gas
exchange
characteristics.
Cultivar
differences
between
`Bluecrop'
and
'Jersey'
in
A
were
not
significant
when
expressed
on
a
leaf
area,
leaf
dry
weight,
or
total
chlorophyll
basis.
Maximum
CO
2
assimilation
rates
for
V.
darrowii
were
about
35%,
50%,
or
40%
lower
than
highbush
cultivars
when
expressed
on
a
leaf
area,
leaf
dry
weight,
or
total
chlorophyll
basis,
respectively.
Differences
between
`Bluecrop'
and
'Jersey'
were
also
non-
significant
for
mesophyll
conductance,
transpiration,
CO
2
compensation
points,
and
water
use
efficiency.
CO
2
assim-
ilation
maximized
between
600-800
µmol•s
-
l•m
-2
photosynthetic
photon
flux
(PPF)
for
all
three
genotypes
and
the
temperature
optima
ranged
between
18°
and
26°C
for
'Jersey',
14°
and
22°
for
`Bluecrop',
and
25°
and
30°
for
V.
darrowii.
As
temperature
was
increased
from
20°
to
30°,
leaf
conductance
(g
1
)
to
water
vapor
was
lower
and
water
use
efficiency
was
higher
for
V.
darrowii,
compared
to
`Bluecrop'
but
not
'Jersey'.
There
was
a
50-65%
reduction
in
g
1
as
VPD
was
increased,
but
only
10-20%
reduction
was
observed
in
A.
Leaf
conductance
to
water
vapor
was
reduced
for
V.
darrowii,
which
restricted
intercellular
CO
2
.
Since
crosses
are
possible
between
highbush
and
V.
darrowii,
it
is
possible
that
heat
tolerance
and/or
drought
resistance
could
be
improved
in
Highbush
blueberry
through
the
incorporation
of
genes
from
V.
darrowii.
Environmental
effects
on
CO
2
assimilation
and
related
gas
exchange
parameters
have
been
widely
investigated
in
fruit
crops
(8,
9,
11,
14,
27,
28).
These
investigations
provide
useful
in-
formation
for
evaluating
environmental
limitations
to
productiv-
ity,
as
well
as
providing
insight
into
cultural
or
genetic
means
for
improving
their
water
and
carbon
efficiency.
Gas
exchange
characteristics
differ
in
plants
adapted
to
dif-
ferent
environmental
habitats
(8),
and
their
successful
adapta-
tion
may
depend
upon
differences
in
CO
2
assimilation
(A),
transpiration
(E),
or
water
use
efficiency
(WUE).
Highbush
blueberry
(Vaccinium
corymbosum)
is
well-adapted
to
sandy
organic
soils
of
low
pH,
and
plants
are
reported
to
perform
poorly
under
drought
conditions
and
high
temperature
(10).
In
contrast,
V.
darrowii,
a
wild
diploid
blueberry
species,
is
well-
adapted
to
dry
sites
and
high
air
temperature
in
the
Southeastern
United
States
(3,
10,
19).
The
objectives
of
this
study
were
a)
to
characterize
the
gas
exchange
response
of
'Jersey'
and
`Bluecrop'
highbush
blue-
Received
for
publication
9
Oct.
1985.
Michigan
Agricultural
Experiment
Station
Article
no.
11673.
A.D.
Draper,
USDA,
Beltsville,
Md.
provided
plant
material
used
in
this
study.
The
cost
of
publishing
this
paper
was
defrayed
in
part
by
the
payment
of
page
charges.
Under
postal
regulations,
this
paper
therefore
must
be
hereby
marked
advertisement
solely
to
indicate
this
fact.
'Present
address:
Department
of
Plant
Science,
Univ.
of
Arizona,
Tucson,
AZ
85721.
berry
and
V.
darrowii
in
relation
to
light,
CO
2
,
temperature,
and
vapor
pressure
deficit;
b)
to
evaluate
the
role
of
stomata'
control
over
water
use
efficiency
under
conditions
of
high
tem-
perature
and
high
vapor
pressure
deficits
(environmental
con-
ditions
often
associated
with
drought);
and
c)
to
determine
if
there
are
differences
between
V.
darrowii
and
highbush
blue-
berry
in
response
to
temperature
or
vapor
pressure
deficit.
if
useful
adaptations
in
gas
exchange
properties
occur
and
if
they
are
heritable,
they
might
be
incorporated
into
highbush
blue-
berry
to
broaden
its
horticultural
range.
Materials
and
Methods
Plant
material.
One-year-old
rooted
cuttings
of
Bluecrop'
,
`Jersey',
and
a
selection
of
V.
darrowii
(Fla.
4B)
were
grown
under
14-hr
photoperiods
in
a
glasshouse,
and
supplemental
light
was
provided
by
1000-W
metal
halide
lamps
(GE
1000W
M47
BU/H36).
Photosynthetic
photon
flux
(PPF)
at
plant
level
during
the
growth
and
maturation
of
the
vegetative
flush
used
for
measurements
ranged
from
maxima
of
650-1400
to
mirtinla
of
85-225
[Lmobs
-1
•111
-2
.
The maximum
day
temperatures
rang
from
18°-36°C,
and
the
minimum
night
temperatures
from
18
27°.
Fertilizer
[200
ppm
N,
100
ppm
P,
100
ppm
K,
50
ppm
Mg,
100
ppm
Fe,
(by
weight)]
was
added
to
water
used
tbor
irrigation
as
needed
to
maintain
healthy
leaf
tissue.
Phosphori
c
acid
was
used
to
adjust
the
pH
of
the
water
to
5.0.
Gas
exchange
measurements.
Measurements
were
made
01.1
134
J.
Amer.
Soc.
Hort.
Sci.
112(0:134-138.
198r71
A
r
2
=0.936
a
y=1
4.62(1
-e
-0
00282
)
-1
.3
B
r2=0.959
,
a
a
v
a
.11
y=1
5.58(1
-e
-0
3
2,51
x)
-2
C
r
2
=0.976
a
y=1
0.33(1
-e
-0
0038
x)
-1
.3
0
400
'
800
'
12
t
00
1
600
Table
1.
A
comparison
of
gas
exchange
characteristics
between
o
uc
crop',
'Jersey',
and
V.
darrowii
under
optimum
environmental
eonditions.4
Gas
exchange
parameter
Bluecrop
Jersey
V.
darrowii
A
(
p,rnol
CO
2
/m
2
per
sec)
A
(Pool
CO
2
/kg
dry
wt
per
sec)
A
(p.mol
CO
2
/g
chlorophyll
per
see)
(owl
H
2
0/m
2
per
sec)
yttJE
(p.mol
COilmmol
H
2
O)
gra
(
m
mol
CO
2
/m
2
per
sec)
co
t
compensation
point
(p.l.liter
-
I)
park
respiration
(Imo!
CO
2
/m
2
per
sec)
,m
cs
ophyll
conductance
(g,,)
and
CO
2
compensation
point
were
esti-
mated
from
the
linear
portion
of
the
response
of
CO
2
assimilation
(A)
I
to
increasing
intercellular
CO,,
whereas
mean
values
for
A,
transpir-
at
ion
(E),
and
water
use
efficiency
(WUE)
were
determined
from
rep-
i
ca
tions
having
the
highest
rate
of
A
as
taken
from
light
and
CO
2
response
curves.
'Jersey'
and
`Bluecrop'
were
measured
at
21.2°C
1,50),
a
leaf-to-air
vapor
pressure
deficit
(VPD)
of
1.06
kPa
0.26),
s
aturating
PPF
of
1020.6
woks
-1
.m
-
2
(
±
37.4),
and
at
ambient
CO
2
levels
of
328.5
p.1.1iter
-
I
5.1).
V.
darrowii
was
measured
at
30.7°
0.5°),
a
VPD
of
1.08
kPa
0.37),
saturating
PPF
of
1017
p,mol•s
-
I
•m
-2
24.4),
and
at
ambient
CO
2
levels
of
337.7
pl•liter
-
11.4).
11.86
11.51
8.55
1.90
2.00
1.04
19.03
19.39
13.45
2.37
2.20
1.71
4.89
5.43
5.00
96.50
77.50
53.30
42.30
41.90
88.80
1.57
1.61
1.06
16
4
0
16
tn
12
8
0
16
If)
12
E
6
8
E
4
0
attached
leaves
of
8-
to
12-week-old
terminal
shoots
of
lateral
branches.
The
terminal
18
to
20
leaves
of
an
actively
growing
shoot
of
V.
darrowii
and
the
terminal
one
to
three
fully
ex-
panded
leaves
of
highbush
cultivars
were
enclosed
in
environ-
mentally
controlled
leaf
chambers.
Measurements
were
made
in
an
open
gas
exchange
system
previously
described
by
Sams
and
Fiore
(21),
in
which
light
intensity
(0-2000
limol•s
-l
•m
-2
),
am-
bient
CO
2
(0-1000
µ1.1iter
-1
),
temperature
(10°-45°C),
and
va-
por
pressure
deficit
(0.5-3.5
kPa)
could
be
monitored
and
controlled.
Measurements
were
made
on
four
different
plants,
and
20
determinations
were
made
per
leaf
per
treatment
level.
Light
response
curves
were
determined
by
exposing
leaves
to
saturating
PPF
and
subsequently
decreasing
the
PPF
stepwise.
The
data
were
fitted
by
computer
to
an
asymptotic
curve
of
the
form
y
=
a*ebx
(21).
The
temperature
response
curves
were
determined
by
measuring
gas
exchange
after
initially
exposing
the
plant
material
to
10°-15°C.
Leaf
temperature
subsequently
was
increased
in
to
increments.
Vapor
pressure
deficit
was
maintained
at
<1
kPa
as
temperature
was
increased.
The
data
were
fitted
to
quadratic
equations
using
normal
equations
as
described
by
Little
and
Hills
(15).
The
response
to
differing
levels
of
ambient
CO
2
was
derived
by
exposing
plant
material
to
a
low
CO
2
concentration
(90-120
[kl•liter
-1
)
and
subsequently
increasing
CO
2
concentration
step-
wise
to
800-900
µ1.1iter
-1
.
A
logarithmic
curve
was
fitted
to
the
data
for
CO
2
assimilation
vs.
increasing
intercellular
CO
2
.
Mesophyll
conductance
and
CO
2
compensation
points
were
de-
termined
from
linear
regression
between
intercellular
CO
2
(0-
250
111.liter
-1
)
and
CO
2
assimilation.
Gas
exchange
response
to
vapor
pressure
deficit
was
deter-
mined
by
exposing
plant
material
to
low
vapor
pressure
deficits
(0.5-I
kPa)
and
subsequently
increasing
the
vapor
pressure
def-
telt
in
step
increments
(035-1
kPa)
up
to
3
kPa.
Chlorophyll
determination.
Chlorophyll
was
extracted
from
a
2.0-cm
2
leaf
disk
or
four
to
six
leaves
of
V.
darrowii
using
NN-dimethylformamide
as
described
by
Moran
and
Porath
(20),
using
100
ml
of
solvent
per
5
to
10
g
fresh
weight
of
tissue.
Samples
were
kept
in
the
dark
at
5
°
C
for
48
hr,
then
absorbance
PPFD
µm01
s
-1
M
-2
Fig.
1.
Effects
of
photosynthetic
photon
flux
(PPF)
on
CO
2
assimi-
lation
(A)
in
`Bluecrop'
(A),
'Jersey'
(B),
and
V.
darrowii
(C).
Measurements
were
made
at
20°C
for
`Bluecrop'
and
'Jersey'
and
30°
for
V.
darrowii.
Each
value
is
the
mean
of
20
determinations
and
different
symbols
represent
different
plants.
was
read
at
both
663
and
645
nm
using
a
Beckman
spectropho-
tometer.
Calculations
of
total
chlorophyll
were
made
using
the
equations
of
Arnon
(1).
Data
analysis.
Gas
exchange
parameters
were
calculated
as
molar
fluxes
using
the
mole
fractions
of
water
vapor
and
CO
2
as
suggested
by
Cowan
(4).
The
calculations
were
made
using
computer
programs
described
by
Moon
and
Flore
(18).
Data
were
analyzed
as
a
completely
randomized
design
with
each
plant
being
a
replication
(n
=
4).
Unless
otherwise
indicated,
gas
exchange
measurements
were
made
at
saturating
light
intensities
(1000
pumol•s
-
l•m
-2
),
a
leaf
temperature
of
30°C
for
V.
darrowii
and
20°
for
the
highbush
cultivars,
ambient
CO
2
concentrations
of
320-345
fil•liter
-1
,
and
a
leaf-to-air
vapor
pressure
deficit
of
<1
kPa.
Plant
material
was
allowed
to
equilibrate
for
at
least
1
hr
under
the
respective
initial
treatment
(PPF,
CO
2
,
temperature,
or
VPD)
level
before
measurements
were
made.
Following
a
step
change
in
treatment
level,
plant
material
was
allowed
to
equilibrate
for
2
hr
to
assure
a
steady
state
condition
to
allow
for
calculations
of
intercellular
CO
2
.
Results
Maximum
CO
2
assimilation
rate
(A)
was
similar
for
'Jersey'
and
`Bluecrop'
whether
expressed
on
a
leaf
area,
leaf
dry
weight,
or
a
total
chlorophyll
basis
(Table
1),
whereas
maximum
rate
for
V.
darrowii
was
lower.
Transpiration
(E)
was
also
lower
for
V.
darrowii
than
for
highbush
blueberry,
but
this
lower
rate
of
water
loss
did
not
improve
calculated
water
use
efficiencies
(Table
1).
Dark
respiration
was
about
10-15%
of
A
(Table
1).
Carbon
dioxide
assimilation
for
leaves
approached
light
sat-
J.
Amer.
Soc.
Hort.
Sci.
112(1):134-138.
1987.
135
A
r
2
=
0
.
898
.
a
_
0.9
7,
e
-00044,x
y=159.5(1
—0.0001
2*X
2
)
B
r
2=
.
89
9
y=33.8(1-1.2*e
-
°.°
5
*X-0.001
1
0(
2
)
C
r
2
=
0
.
63
2
a
°
y=718.7(1-1.1*e
-00
°
2
*X-0.00004*X
2
)
200
400
6'0
INT
CO
2
p,mol/mol
800
250
um
200
3
150
3
0
100
3
4
50
C
250
200
3
150
9
0
100
3
50
.
1
.
•••
250
200
3
150
0
3
1003
,
50
1.
18
0)
15
t
E
12
75
9
E
3.
tn
a
9
co
15
E
12
<
3
0
6
3
0
18
6
3
0
18
15
12
9
6
8
0
7
ri)
12
O
E
E
0
N
12
E
E
0
8
0
10
20
30
40
TEMPERATURE
°
C
Fig.
2.
Effects
of
leaf
temperature
CO
2
assimilation
(A)
in
`Bluecrop'
(A),
'Jersey'
(B),
and
V.
darrowii
(C).
Measurements
were
made
at
1000
1.1.,mol•s
-
LIT1
-2
PPF.
Each
value
is
the
mean
of
20
determi-
nations
and
different
symbols
represent
different
plants.
uration
level
at
PPF
of
600-800
limol.S
-1
.n1
-2
for
'Jersey'
and
V.
darrowii
(Fig.
1
B
and
C),
whereas
the
light
saturation
level
for
'Bluecrop'
was
observed
to
be
at
a
slightly
higher
PPF
of
700-900
p,mol.s
-1
.m
-2
(Fig.
1A).
CO
2
assimilation
increased,
then
declined
with
increasing
temperature
in
all
three
genotypes
(Fig.
2).
The
optimum
temperature
for
A
ranged
between
18°
to
26°C
for
'Jersey'
(Fig.
2B),
between
14°
to
22°
for
`Bluecrop'
(Fig.
2A),
and
between
25°
to
30°
for
V.
darrowii
(Fig.
2C).
Carbon
dioxide
assimilation
increased
and
gi
decreased
(Fig.
3)
in
all
three
genotypes
as
CO
2
levels
were
increased.
CO
2
com-
pensation
points
were
lower
and
mesophyll
conductance
(g
m
)
was
higher
for
highbush
cultivars
than
for
V.
darrowii
(Table
1).
Increasing
leaf
temperature
from
20°
to
30°
significantly
re-
duce
A
and
g1
in
`Bluecrop'
but not
in
'Jersey'
(Table
2),
whereas
there
was
a
small
insignificant
increase
in
A
and
decrease
in
g
i
for
V.
darrowii
(Table
2).
Transpiration
increased
in
all
three
genotypes
with
a
temperature
increase
from
20°
to
30
°
,
but
the
increase
was
only
significant
for
V.
darrowii
(Table
2).
How-
ever,
calculated
WUE
was
reduced
significantly
in
all
three
genotypes
with
the
temperature
increase
from
20°
to
30°
(Table
2).
As
temperature
increased,
residual
conductance
(g
r
)
de-
creased
significantly
for
`Bluecrop'
but
not
'Jersey',
whereas
there
was
a
significant
increase
for
V.
darrowii
(Table
2).
Increasing
VPD
from
1
to
3
kPa
significantly
reduced
A
in
`Bluecrop'
(Fig.
4A
and
Table
3),
and
V.
darrowii
(Fig.
4C
and
Table
3),
but
not
in
'Jersey'
(Fig.
4B
and
Table
3),
whereas
g
1
declined
in
all
three
genotypes
as
VPD
increased
from
1
to
3
kPa
(Fig.
4
and
Table
3).
Increasing
VPD
from
1
to
3
kPa
increased
transpiration
rates
significantly
and
decreased
WUE
Fig.
3.
Effects
of
intercellular
CO
2
levels
on
CO
2
assimilation
(A)
and
stomatal
conductance
(g
s
)
in
`Bluecrop'
(A),
'Jersey'
(B),
and
V.
darrowii
(C).
Measurements
were
made
at
saturating
PPF
(1000
ilmol•s
-I
•m
-2
)
and
at
20°C
for
13luecrop'
and
'Jersey'
and
at
30°
for
V.
darrowii.
Each
value
is
the
mean
of
20
determinations
with
open
symbols
representing
A
and
solid
symbols
representing
g
s
.
Different
symbols
represent
different
plants.
(Table
3).
Increasing
VPD
decreased
intercellular
CO
2
levels
(Table
3).
Discussion
Maximum
CO
2
assimilation
rates
under
optimum
conditions
were
25-35%
higher
for
highbush
than
rates
for
V.
darrowii
blueberry
and
were
about
2
times
those
reported
for
rabbiteye
blueberry
(24),
50%
lower
than
rates
reported
for
apple
(2,
26);
and
15%
lower
than
maximum
rates
reported
for
peach,
plumi
and
cherry
(7).
Carbon
dioxide
assimilation
increased
in
an
asymptotic
man-
ner
with
increasing
PPF
for
all
three
genotypes.
The
light
sat-
uration
range
of
600-800
p,mol.s
-
I
.m
-2
was
similar
to
saturation
levels
reported
for
other
fruit
crops
(5,
7,
9,
13,
26)
and
for
rabbiteye
blueberry
(24).
The
mesophyll
conductance
of
`Bluecrop'
(96.5
mmol
CO2/
m
2
per
sec)
and
'Jersey'
(77.5
mmol
CO
2
/m
2
per
sec)
was
similar
to
values
reported
for
almond,
plum,
peach,
and
cherry
(7)
and
CO
2
compensation
points
were
typical
of
those
reported
for
C-3
spp.
Mesophyll
conductance
was
lower
(53.3
mmo1
CO
2
/m
2
per
sec)
in
V.
darrowii
compared
to
the
highbush
ad"
tivars.
This
lower
capacity
for
A
may
reflect
the
lower
range
of
g
1
observed,
which
restricts
intercellular
CO
2
concentration
.
A
similar
restriction
in
g
m
due
to
stomatal
aperture
has
been
reported
for
apricot,
some
cultivars
of
which
are
adapted
t
°
,
desert
conditions
(8).
CO
2
assimilation
increased
rapidly
in
a
h
'
three
genotypes
in
response
to
increasing
intercellular
CO2
con"
centrations
up
to
250
pl.liter
-
I
,
and
then
the
rate
of
increase
declined
due
to
limitations
presumably
imposed
by
the
turno
ver
of
the
carboxylase
enzyme.
136
J.
Amer.
Soc.
Hort.
Sci.
112(1):134-138.
198i
Change
30°C
(%)
Change
20°C
30°C
(%)
20°C
8.2
-19.6
175.7
ab
143.4
ab
-18.4
1.90
b
7.6
-29.0*
237.3
a
155.8
a
-34.3*
2.69
a
8.8
8.6
117.5
b
93.1
b
-20.8*
1.45
b
A
(p.mol•s
-1
.m
-2
)
Change
gr
(Minas
-1
.m
-2
)
Change
E
(mmol•s
-2
-m
-2
)
Change
CO2i
WUE
(Rmol•mol
-1
)
(p,mol
CO
2
/mmol
H
2
0)
Change
Change
tn
240
3
3
160
(2
3
-80
240
3
3
160
c2
80
ID
240
3
160
-
o
3
0
bit
2,
Effect
of
leaf
temperature
on
the
gas
exchange
characteristics'
of
'Jersey',
`Bluecrop',
and
V.
darrowii
blueberry.
Gas
exchange
parameter
A
g,
(Rmol.s
-1
.m
-2
)
(mmol.s
-1
.m
-2
)
Genotype
20°C
J
e
rsey
10.2
abY
Bluecrop
10.7
a
V.
darrowa
8.1
b
E
(mmol.s
-1
.m
-2)
Change
30°C
(%)
20°C
30°C
2.38
25.3
46.5
43.6
3.04
13.0
42.5
32.3
2.39
64.8*
29.6
49.9
WUE
(µn&
CO
2
/mmo1H
2
O)
Change
(%)
-29.6*
-37.5**
-33.9**
gr
(mmol.s
-
I.m
-2
)
Change
(%)
20°C
30°C
-6.2
5.4
3.8
a
-24.0**
4.0
2.5
b
68.6*
5.6
3.7
a
/CO
2
assimilation
w
ere
measured
at
deficits
<1
kPa.
YMea
n
separation
(A),
leaf
conductance
to
water
vapor
(g
1
),
transpiration
(E),
residual
conductance
to
CO
2
(g
r
),
and
water
use
efficiency
(WUE)
a
saturating
PPF
of
1012
p.mol.s
.-
I.in
-2
(
±
22.3),
ambient
CO
2
concentrations
of
332-343
p.l.liter
-1
,
and
at
vapor
pressure
within
columns
by
Tukey's
w-test,
5%
level;
separation
between
vapor
pressure
deficit,
*
=
5%
level,
**
=
1%
level.
able
3.
Effect
of
vapor
pressure
deficit
on
the
gas
exchange
characteristics'
of
'Jersey',
`Bluecrop',
and
V.
darrowii
blueberry.
Gas
exchange
parameter
G
e
notype
1
kPa
3
kPa
(%)
1
kPa
3kPa
(%)
1
kPa
3
kPa
(%)
1
kPa
3
kPa
(%)
1
kPa
3
kPa
(%)
ersey
9.1
8.3
-8.8
236.4
by
104.8
b
-55.7*
1.95
a
3.45
a
79.9*
267.2
a
202.1
ab
-24.4*
4.7
2.6
-44.7*
Bluecrop
10.6
8.4
-20.8*
323.1
a
130.4
a
-59.6*
2.25
a
3.75
a
66.7*
281.6
a
225.7
a
-
19.9*
4.8
2.6
-45.8*
.
darrowii
8.9
7.4
-
16.9*
168.2
b
85.4
c
-49.2*
1.38
b
2.68
b
94.2*
244.1
b
190.1
b
-22.1*
6.5
2.8
-56.9*
zCO
2
assimilation
(A),
leaf
conductance
to
water
vapor
(g
1
),
transpiration
(E),
intercellular
CO
2
(CO
2i
),
and
water
use
efficiency
(WUE)
were
measured
at
26.2°C
for
'Jersey'
and
13lueerop'
and
29.8°
for
V.
darrowii,
a
PPF
of
1009
p.mol.s
-
'•m
-2
36),
and
at
ambient
CO
2
concentrations
of
328.8
t..1,1•1iter
-1
4.0).
Mean
separation
within
columns
by
Tukey's
w-test,
5%
level;
separation
between
vapor
pressure
deficit,
*
=
5%
level.
A
• •
B
C
0
5
1.5
2.5
3.5
VPD
KPa
Fig.
4.
Effects
of
vapor
pressure
deficit
(VPD)
on
CO
2
assimilation
(A)
and
stomatal
conductance
(g
5
)
in
'Elluecrop'
(A),
'Jersey'
(B),
and
V.
darrowii
(C).
Measurements
were
made
at
saturating
PPF
(1000
p.mol
s
-
'•
m
-2
)
and
at
26°C
for
`Bluecrop'
and
'Jersey'
and
at
30°
for
V.
darrowii.
Each
value
is
the
mean
of
20
determinations
with
open
symbols
representing
A
and
solid
symbols
representing
g
i
.
Different
symbols
represent
different
plants.
Amer.
Soc.
Hort.
Sci.
112(1):134-138.
1987.
Stomatal
closure
in
response
to
increasing
VPD
has
been
observed
in
most
species
of
plants
investigated
(22,
23).
How-
ever,
studies
with several
woody
perennials
have
indicted
that
g1
effects
on
E
due
to
increasing
VPD
were
small,
and
that
substantial
increases
in
E
occurred
in
these
species
at
high
VPDs.
With
the
highbush
blueberry
cultivars
and
V.
darrowii,
g
1
was
reduced
by
about
50%
when
VPD
was
increased
from
1
to
3
kPa,
but
there
was
only
a
modest
reduction
in
A
of
10-20%
(Table
3).
Thus,
reduction
of
g
i
in
blueberry
due
to
increasing
VPD
imposed
a
greater
restriction
on
E
per
unit
of
VPD
than
on
A.
Similar
responses
have
been
observed
in
douglas-fir
(16,
17)
and
Sitka
spruce
(28).
The
fact
that
g
i
was
more
sensitive
to
VPD
than
A
suggests
that
blueberry
does
not
possess
a
strong
feedback
on
stomatal
aperture
that
maintains
intercellular
CO
2
constant
(Table
3).
There
is
a
strong
coupling
between
g1
and
A
in
apple
(14).
The
range
of
g
1
reported
for
deciduous
fruit
trees
is
90
to
320
mmol
H
2
0/m
2
per
sec
and
64
to
220
for
other
deciduous
woody
plants
(12).
Leaf
conductance
values
for
`Bluecrop'
(323.1)
and
`Jersey'
(236.4)
at
26°C
and
1
kPa
were
at
the
upper
limit
of
the
range
reported
for
woody
perennials,
but
compared
favor-
ably
with
g
1
values
reported
for
peach,
plum,
and
cherry,
which
were
measured
under
similar
conditions
(6).
Thus,
the
stomatal
control
of
water
loss
in
highbush
blueberry
was
similar
to
that
observed
in
other
fruit
crops.
Transpiration
rates
and
WUE
for
highbush
blueberry
were
also
similar
to
values
reported
for
Pm-
nus
species
(7).
V.
darrowii
possesses
very
low
values
of
g
1
at
both
1
(168.2)
and
3
kPa
(85.4),
which
may
account
for
the
lower
rates
of
A
and
E
observed,
compared
to
highbush
blue-
berry.
No
evidence
was
obtained
in
this
study
that
inefficient
sto-
matol
control
over
water
loss
under
high
vapor
pressure
deficits
137
12
9
0
6
E
3
0
7
12
co
E
9
To'
6
E
<
0
7
12
I
E
9
-
5
6
E
0
is
responsible
for
highbush
blueberry's
poor
adaptation
to
drought.
However,
the
WUE
of
highbush
blueberry
might
be
improved
through
plant
breeding
if
parents
could
be
identified
that
restrict
transpirational
losses
through
low
values
of
g1
without
imposing
too
large
a
restriction
on
A.
The
general
shape
of
the
temperature
response
curves
was
parabolic
with
a
decline
in
A
at
high
temperature.
The
response
to
temperature
was
independent
of
humidity
up
to
30°C,
as
VPD
was
controlled
at
less
than
1
kPa.
At
temperatures
above
30°,
VPD
could
not
be
stabilized
at
gradients
less
than
1
kPa
because
the
laboratory
temperature
could
not
be
raised
sufficiently
to
prevent
condensation
of
water
vapor
in
the
gas
lines.
VPDs
ranged
up
to
1.7
kPa
at
high
temperatures.
The
reduction
in
net
CO
2
assimilation
rate
at
high
temperature
was
not
as
severe
as
some
reported
in
many
previous
studies,
probably
because
VPD
was
held
constant
as
temperature
increased.
However,
this
heat-
ing
of
the
laboratory
room
may
have
affected
g
i
,
as
most
of
the
plant
was
incubating
at
temperatures
greater
than
leaves
en-
closed
in
sample
chambers.
This
differential
may
explain
the
lower
values
of
g
1
observed
in
Table
2
compared
to
the
VPD
response
(Table
3).
Since
these
experiments
were
several
hours
in
length,
a
message
that
caused
a
reduction
in
g
1
could
have
been
transmitted
to
levels
within
sample
chambers.
The
broad
temperature
optimum
range
(18
°
-26
°
)
for
'Jersey'
was
similar
to
ranges
reported
for
walnut
(25)
and
pecan
(6),
whereas
'Blue-
crop'
had
a
lower
temperature
optimum
(14°-22
°
)
than
those
observed
for
other
fruit
crops
(5,
14,
21).
The
temperature
op-
timum
for
V.
darrowii
was
between
25°-30°,
which
is
8
°
to
10°
higher
than
`Bluecrop'
,
but
similar
to
temperature
optimums
reported
for
peach
(5),
apple
(14),
and
cherry
(21).
Leaf
con-
ductance
at
20
°
and
30°
was
much
lower
for
V.
darrowii
and
`Jersey'
than
for
`13luecrop'.
Thus
'Jersey'
and
V.
darrowii
may
possess
a
greater
tolerance
to
high
temperatures
and
drought
conditions
through
restriction
of
water
loss
by
decreasing
sto-
matal
aperture.
Such
a
response
also
has been
suggested
in
rabbiteye
blueberry,
which
is
reported
to
be
drought
resistant
(10,
19,
24),
and
exhibits
even
lower
ranges
of
g
i
than
V.
dar-
rowii
(24).
The
restriction
of
water
loss
under
conditions
of
high
evaporative
demand
may
more
than
compensate
for
the
slightly
lower
rates
of
A
in
these
drought-resistant
blueberries.
V.
darrowii
and
'Jersey'
may
possess
a
heritable
component
favoring
survival
at
higher
temperatures.
Similar
types
of
eco-
logical
differentiation
have
been
reported
in
other
species
(3).
Literature
Cited
1.
Amon,
D.I.
1949.
Copper
enzymes
in
isolated
chloroplasts.
Plant
Physiol.
24:1-15.
2.
Every,
D.J.
1977.
Maximum
photosynthetic
rate-a
case
in
ap-
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