Flooding, gas exchange and hydraulic root conductivity of highbush blueberry


Davies, F.S.; Flore, J.A.

Physiologia Plantarum 67(4): 545-551

1986


Highbush blueberry plants (Vaccinium corymbosum cv. Bluecrop) growing in containers were flooded in the laboratory for 1-2, 10-14 or 35-40 days. The effects on carbon assimilation, photosynthetic response to varying CO2 and O2 concentrations, and apparent quantum yield were measured in an open flow gas analysis system, and the hydraulic conductivity of the root was measured using a pressure chamber. Root conductivity was lower, and the effect of increasing CO2 levels on carbon assimilation was less, for flooded than for unflooded plants. A reduction in O2 levels surrounding the leaves, from 21 to 2%, increased carbon assimilation in unflooded plants by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO2 fixed/mol CO2. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O2, averaging 0.005 mol CO2 fixed/mol CO2. Apparent quantum yield decreased from 2.2 x 10-1 mol of CO2 fixed/mol light for unflooded plants to 2.0 x 10-3 and 9.0 x 10-4 for intermediate- and long-term flooding durations, respectively. Short-term flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf, indicating that the highbush blueberry is physiologically intolerant to flooding and appears to survive prolonged flooding via stomatal closure rather than through morphological or anatomical adaptations as observed in other plants.

PHYSIOL.
PLANT.
67:
545-551.
Copenhagen
1986
Flooding,
gas
exchange
and
hydraulic
root
conductivity
of
highbush
blueberry
Frederick
S.
Davies
and
James
A.
Fiore
Davies,
F.
S.
and
Fiore,
J.
A.
1986.
Flooding,
gas
exchange
and
hydraulic
root
con-
ductivity
of
highbush
blueberry.
Physiol.
Plant.
67:
545-551.
Highbush
blueberry
plants
(Vaccinium
corymbosum
L.
cv.
.
Bluecrop)
growing
in
con-
tainers
were
flooded
in
the
laboratory
for
various
durations
to
determine
the
effect
of
flooding
on
carbon
assimilation,
photosynthetic
response
to
varying
CO
2
and
0,
con-
centrations
and
apparent
quantum
yield
as
measured
in
an
open
flow
gas
analysis
sys-
tem.
Hydraulic
conductivity
of
the
root
was
also
measured
using
a
pressure
chamber.
Root
conductivity
was
lower
and
the
effect
of
increasing
CO,
levels
on
carbon
assimi-
lation
less
for
flooded
than
unflooded
plants
after
short-(1-2
days),
intermediate-
(10-14
days)
and
long-term
(35-40
days)
flooding.
A
reduction
in
0,
levels
surround-
ing
the
leaves
from
21
to
2%
for
unflooded
plants
increased
carbon
assimilation
by
33%
and
carboxylation
efficiency
from
0.012
to
0.021
mol
CO
2
fixed
(mol
CO
2
)
-
.
Car-
boxylation
efficiency
of
flooded
plants,
however,
was
unaffected
by
a
decrease
in
per-
centage
0
2
,
averaging
0.005
mol
CO,
fixed
(mol
CO,)
-
'.
Apparent
quantum
yield
de-
creased
from
2.2x
10
-
`
mol
of
CO,
fixed
(mol
light)
-1
for
unflooded
plants
to
2.0x
10'
and
9.0x
10'
for
intermediate-
and
long-term
flooding
durations,
respectively.
Short-
term
flooding
reduced
carbon
assimilation
via
a
decrease
in
stomatal
conductance,
while
longer
flooding
durations
also
decreased
the
carboxylation
efficiency
of
the
leaf.
Additional
key
words
Carbon
assimilation,
photosynthesis,
stomatal
conductance,
transpiration,
Vaccinium
corymbosum.
E
S.
Davies,
(reprint
requests),
Dept
of
Fruit
Crops,
Univ.
of
Florida,
Gainesville,
FL
32611,
USA;
J.
A.
Fiore,
Dept
of
Horticulture,
Michigan
State
Univ.,
East
Lansing,
MI
48824,
USA.
Introduction
Highbush
blueberries
are
native
to
bogs
of
the
north-
eastern
and
northern
United
States.
Cultivated
high-
bush
plants
are
generally
flooding-sensitive
under
field
conditions
(Kender
and
Brightwell
1966);
however,
they
are
flooding-tolerant
under
controlled
conditions
unless
Phytophthora
root
rot
becomes
a
problem
(Ab-
bott
and
Gough
1985,
Davies
and
Fiore
1986).
Korchak
(1983)
found
highbush
plants
to
be
more
sensitive
to
low
0
2
levels
in
the
soil
than
other
Vaccinium
species.
Growth
of
highbush
and
rabbiteye
(V.
ashei)
species
generally
ceases
after
4-7
days
of
flooding
(Davies
and
Wilcox
1984,
Davies
and
Fiore
1986).
Gas
exchange
characteristics
of
many
plant
species
are
altered
under
flooded
conditions.
Stomata]
conduct-
ance
decreased
due
to
flooding
within
6
days
for
Citrus
aurantium
(Syvertsen
et
al.
1983),
Prunus
sp.
(Ander-
sen
et
al.
1984a),
Populus
seedlings
(Periera
and
Koz-
lowski
1977)
and
Liquidambar
styraciflua
(Pezeshki
and
Chambers
1985).
Flooding
also
adversely
affects
carbon
assimilation
in
a
wide
range
of
species
including
Malus
domestica
(Childers
and
White
1942),
Lycopersicon
es-
culentum
(Brix
1962),
Populus
deltoides
(Regehr
et
al.
1975),
Citrus
sinensis
(Phung
and
Knipling
1976),
Liqui-
dambar
styraciflua
(Pezeshki
and
Chambers
1985)
and
Vaccinium
ashei
(Davies
and
Flore
1985).
The
decrease
in
carbon
assimilation
was
attributed
to
stomata]
factors
in
some
species
(Regehr
et
al.
1975,
Phung
and
Knipling
1976)
and
non-stomatal
factors
in
others
(Childers
and
White
1942,
Guy
and
Wample
1984),
including
feed-
Received
15
September,
1985;
revised
30
January,
1986;
in
final
state
19
March,
1986
Physiol.
Nam.
67,
1986
545
back
inhibition
of
photosynthesis
due
to
starch
accumu-
lation
during
flooding
(Wample
and
Thornton
1984).
Pereira
and
Kozlowski
(1977)
suggested
that
stomatal
closure
resulted
from
an
interruption
of
hormone
trans-
location
from
root
to
shoot.
In
contrast
Davies
and
Wil-
cox
(1984)
observed
a
rapid
increase
in
V
(values
be-
came
less
negative)
of
rabbiteye
blueberry
with
root
ex-
cision
and
suggested
that
hydraulic
conductivity
of
the
root
and
cell
turgor
were
regulating
g,.
Similarly,
flood-
ing
has
been
shown
to
decrease
root
conductivity
of
to-
bacco
(Kramer
and
Jackson
1954),
citrus
(Syvertsen
et
al.
1983)
and
Pyrus
sp.
(Andersen
et
al.
1984b).
Studies
by
Davies
and
Flore
(1986)
suggested
that
the
stomata'
sensitivity
of
blueberries
to
flooding
varies
with
duration.
Stomata!
conductance
and
transpiration
of
flooded
blueberries
were
responsive
to
changes
in
the
environment
after
1-2
days,
but
became
less
responsive
after
longer
flooding
durations.
Moreover,
carbon
as-
similation
decreased
after
short-term
flooding
(1-2
days),
becoming
zero
or
negative
after
longer
durations
(11-14
days).
Our
objectives
were
to
study
the
effects
of
short-
(1-2
days),
intermediate-
(10-14
days)
and
long-term
(35-40
days)
flooding
on
gas
exchange
of
highbush
blueberries
under
controlled
conditions.
Stomatal
conductance
and
carbon
assimilation
were
monitored
prior
to
gas
ex-
change
measurements
in
the
laboratory
to
minimize
plant-to-plant
variability
observed
in
previous
studies
(Davies
and
Wilcox
1984).
This
ensured
that
plants
would
be
at
similar
physiological
stages
to
those
sug-
gested
by
Davies
and
Flore
(1986).
Abbreviations
-
g'„
residual
conductance
to
CO
2
;
g,,
stomatal
conductance
to
water
vapor;
g'„
stomatal
conductance
to
CO2;
leaf
water
potential.
Materials
and
methods
Plant
material
One-year
old
rooted
cuttings
of
cv.
Bluecrop
highbush
blueberry
(Vaccinium
corymbosum
L.)
were
obtained
from
a
commercial
nursery
in
June
1984
and
placed
into
3.81
plastic
containers
in
a
sand:peat
moss
(1:1,
vlv)
me-
dia.
Plants
were
grown
in
a
polyethylene
greenhouse
at
ca
50%
of
full
sunlight
until
October
18,
after
which
26
uniform
plants
were
transferred
to
the
laboratory
(pho-
ton
flux,
130
umol
20-25°C)
for
flooding
studies.
Plants
were
ca
20-30
cm
in
height
and
had
formed
ter-
minal
buds.
Additional
plants
used
to
determine
the
ef-
fect
of
0
2
on
carbon
assimilation
were
maintained
in
the
greenhouse
until
they
were
moved
to
the
laboratory
on
16
November
1984.
Flooding
Plants
were
paired
visually
for
size
and
vigor,
and
one
plant
from
each
pair
was
flooded
by
placing
the
3.8
I
container
into
a
larger
container
lined
with
plastic
and
applying
tap
water
(20-25°C)
slowly
to
the
root
system.
Plants
were
flooded
on
various
days
from
October
20-24
in
a
staggered
fashion
to
insure
that
there
would
be
plants
at
various
stages
of
flooding
stress
as
outlined
by
Davies
and
Flore
(1986):
a)
Short-term
flooding
where
g,
of
flooded
plants
re-
sponded
to
changes
in
the
environment,
but
was
less
than
that
of
unflooded
plants
(ca
1-2
days).
b)
Intermediate-term
flooding
where
g,
and
carbon
as-
similation
approached
zero
for
flooded
plants
(ca
10-14
days).
c)
Long-term
flooding
where
g,
no
longer
responded
to
the
environment.
Stomata'
conductance
was
zero
and
carbon
assimilation
was
zero
or
negative
(ca
35-40
days).
Leaves
of
plants
were
monitored
daily
beginning
2
days
before
each
stage
using
a
LI
1600
steady
state
porometer
(LI-COR
Inc.
Lincoln,
Nebraska)
for
g,
measurements
and
an
ADC
model
LCA-2
portable
CO,
analyzer
(Analytical
Development
Company,
Hert-
shire,
England)
for
carbon
assimilation
measurements.
Plants
were
selected
for
further
studies
based
on
these
preliminary
measurements
rather
than
duration
of
flooding.
This
system
reduced
plant-to-plant
variability
found
in
previous
flooding
studies
(Davies
and
Wilcox
1984)
and
ensured
that
plants
would
be
at
similar
phys-
iological
stages
during
subsequent
gas
exchange
studies.
Gas
exchange
measurements
Four
flooded
and
4
unflooded
plants
for
short-term
flooding
and
2
plants
each
for
intermediate
and
long-
term
flooding
studies
were
used
for
gas
exchange
meas-
urements.
One
shoot
with
fully
expanded
leaves
was
en-
closed
in
one
of
4
environmentally
controlled
plexiglass
chambers
(15.3
x
10x
10
cm,
length
x
width
x
height)
and
allowed
to
equilibrate
for
1
h
prior
to
measurements.
Gas
exchange
was
monitored
using
an
open
flow
system
consisting
of
a
Beckman
865
infrared
gas
analyzer
and
2
General
Eastern
1100
dew
point
hygrometers
as
de-
scribed
previously
(Sams
and
Flore
1982).
Measure-
ments
were
made
within
optimum
ranges
for
highbush
blueberries
(J.
W.
Moon,
Jr.
1985.
Thesis,
Michigan
State
Univ.,
E.
Lansing,
MI,
USA):
photon
flux,
1
000
jimol
m
-2
s
-
';
leaf
temperature
25°C;
leaf-to-air
vapor
pressure
deficit
1.0-1.5
kPa.
Carbon
assimilation,
g'„
g',
and
g„
were
calculated
as
described
by
Moon
and
Flore
(1986).
Effect
of
CO,
concentration
on
carbon
assimilation
The
effect
of
various
CO,
concentrations
on
carbon
as-
similation
was
studied
for
flooded
and
unflooded
plants
at
each
flooding
stage.
Leaves
were
equilibrated
in
chambers
at
ambient
CO,
(330-350
µl
l
-
'),
and
meas-
urements
performed
stepwise
at
ca
350,
250
and
150
1
-
'
of
ambient
CO,.
Non-ambient
CO,
concentrations
were
prepared
by
mixing
ambient
air
from
which
the
546
Physiol.
Plant.
67,
1996
Y=-0.13+0.021x
r
2
=0.98
0
Y=-0.43+0.014x
r
2
=0.95
8.0
e:
6.0
E
4.0
-
0"
E
2.0
E
e
E
E
00
C01
E
0
E
E
50
40
30
=33
3
20
.9-0.018x
r
2=0.31
0
20
15
10
5
0-ff
too
0
-41
Y=62.7-0.046x
-
r2=0.88
Y=5.9+0.04x
r2=0.96
200
300
400
CCO
2
3
E
(P11-1)
0
Y=9.1+0.01x
r2=0.77
0
CO,
had
been
scrubbed
using
soda
lime
with
air
from
a
compressed
air
tank
which
contained
4
000-5
000
CO,.
The
CO,
concentration
was
continuously
moni-
tored
with
a
Beckman
865
infrared
gas
analyzer
as
pre-
viously
described
by
Sams
and
Flore
(1982)
or
using
an
ADC
Model
LCA-2
infrared
gas
analyzer.
This
range
of
CO,
values
corresponds
to
the
RUP,
saturated
(linear)
phase
of
CO,
response
curves
as
described
by
Farquhar
and
Sharkey
(1982)
and
Moon
and
Flore
(1986)
for
highbush
blueberries.
Effect
of
0,
concentration
on
carbon
assimilation
Two
unflooded
and
2
flooded
(1.5
days)
plants
were
used
to
study
the
effects
of
low
0,
concentration
on
car-
bon
assimilation
of
flooded
and
unflooded
plants.
The
CO,
system
was
adapted
to
use
varying
concentrations
of
CO,
and
0,
by
connecting
0
2
and
N
2
tanks
to
a
gas-
mixing
system
using
needle
valves.
The
0,
flowed
through
a
LIDAR
oxygen
meter
and
then
through
the
system
where
it
was
mixed
with
CO,
and
N,.
The
output
of
the
chambers
was
minitored
continuously
with
an
ADC
CO,
analyzer
as
described
above.
In
this
way
CO,
and
0
2
concentrations
around
the
shoot
could
be
con-
trolled
and
monitored,
Plants
were
allowed
to
equili-
brate
at
330-350
Id
1
-
'
CO,
and
21%
0,
(ambient
condi-
tions).
Carbon
dioxide
concentration
was
then
changed
stepwise
as
above,
after
which
0,
concentration
was
lowered
to
10
and
2%
and
the
procedure
repeated.
Changes
in
carbon
assimilation
occurred
within
1
min
of
changes
in
gas
concentrations.
Apparent
quantum
yield
The
same
plants
used
in
the
CO,
response
studies
were
also
used
to
develop
light
response
curves
and
for
cal-
culation
of
apparent
quantum
yield.
Stomata
were
al-
lowed
to
open
until
stable
values
were
obtained
(ca
1
h;
photon
flux,
1
000
umol
m'
s
-
';
25°C,
vapor
pressure
deficit
1.0-1.5
kPa).
Neutral
density
filters
were
then
placed
over
each
chamber
sequentially
giving
photon
fluxes
of
ca
600,
300,
180,
100
and
50
umol
Plants
were
allowed
to
stabilize
at
each
light
level
for
30
min
prior
to
measurements.
Apparent
quantum
yield
was
calculated
as
the
slope
of
the
linear
portion
of
light
sat-
uration
curves
(Ehleringer
and
BjOrkman
1977).
Hydraulic
conductivity
of
the
root
Following
light
and
gas
exchange
measurements
plants
were
detopped
and
roots
placed
into
a
large
pressure
chamber.
Hydraulic
conductivity
of
the
root
was
meas-
ured
using
a
modified
pressure
chamber
as
described
by
Fiscus
(1975).
The
cut
stem
was
pushed
through
a
cir-
cular
opening
in
the
chamber
lid
to
make
a
tight
seal
and
the
root
submerged
in
18-20°C
water
in
the
cham-
ber
which
was
sealed.
A
pipet
was
attached
to
the
stem
end
via
rubber
tubing
and
0.31
MPa
pressure
was
ap-
plied
to
the
chamber.
Water
movement
through
the
root
was
monitored
for
1
h,
after
which
roots
were
re-
moved
and
cross
sectional
area
of
the
stem
measured.
The
root
was
divided
into
structural
and
fibrous
roots
and
weighed.
We
found
no
effect
of
time
in
the
chamber
on
root
conductivity
within
the
limits
of
our
experiment.
Flow
through
the
root
was
linear
for
pressures
within
0.1-1,0
MPa;
however,
a
pressure
of
0.31
MPa
was
cho-
sen
as
a
realistic
value
based
on
similar
studies
(Wilcox
and
Davies
1983).
Results
and
Discussion
Effect
of
CO
2
concentration
on
carbon
assimilation
Carbon
assimilation
was
linearly
correlated
with
CO,
concentration
for
flooded
and
unflooded
plants
within
the
range
of
150
to
400
ul
I
-
';
however,
carbon
assimila-
tion
was
significantly
less
for
flooded
plants
at
all
flood-
ing
stages
(Figs
1-3).
The
slopes
of
the
CO,
response
curves
differed
for
unflooded
and
flooded
plants
after
short-term
flooding
(Fig.
1)
and
became
substantially
less
for
flooded
plants
after
intermediate-
(Fig.
2)
and
long-term
flooding
(Fig.
3).
During
short-term
flooding,
carbon
assimilation
of
flooded
plants
was
lower
than
that
of
unflooded
plants
and
was
associated
with
lower
although
g',
was
also
significantly
lower
(Fig.
1).
Fig.
1.
Effects
of
CO,
concentration
on
carbon
assimilation
(A),
stomatat
conductance
to
CO,
(g%)
and
residual
conduct-
ance
(g',)
of
unflooded and
flooded
Bluecrop
blueberry
plants.
Plants
were
flooded
for
1-2
days.
unflooded;
0,
flooded.
Physiol.
Plant.
67,
1986
547
8.0
6.0
1.2=0.98
Y=-1.18+0.023x
E
7,
4.0
Y=-0.15+0.005x
r2=0.93
=.
2.0
re
Y=115-0.07x
r2=0.36
Y=36.9-0.05x
r2=0.97
0
30
1=11.31-0.04x
20
10
0
100
200
300
400
1CO
2
7
E
(pl
I
-1
)
E
E
E
f
100
0.1
80
E
60
E
40
ern
20
a
=0.91
y=
3.9+0.01a
r2=0.34
0
Y
=-
0.77+
0.007x
r2=
0.98
'
Y=-0.32+0.001x
r2=0.94
.
Y=42.6+0.034x
in
r2=0.26
60
-
E
z
40
-
E
20
e-
r2=0.88
0I
O
0
if
8.0
-
cf
6.0
£
;4.0
Y=-1.5+0.007x
2.0
-
L
0-1
100
200
300
400
[CO
2
3
E
(II11-1)
Fig.
3.
Effects
of
CO,
concentration
on
carbon
assimilation
(A),
stomata!
conductance
to
CO,
(g',)
and
residual
conduct-
ance
(g',)
of
unflooded
and
flooded
Bluecrop
blueberry
plants.
Plants
were
flooded
for
35-40
days.
IIII,
unflooded;
0,
flooded.
4
1
3.0
Y=7.5-0.01x
Y=1.7+
0.03x
r2=0.99
Stomatal
conductance
tended
to
decrease
at
400
µ1
-1
1
-
'
CO,
possibly
due
to
elevated
internal
CO,
levels
which
approached
260-300
pi
I
-
'.
Transpiration
and
g,
were
also
significantly
less
for
flooded
than
unflooded
plants
at
all
flooding
stages
(data
not
shown).
Similar
re-
sponses
to
flooding
were
noted
by
Davies
and
Flore
(1985)
with
rabbiteye
blueberries.
Stomatal
conduct-
ance
to
CO,
continued
to
decrease
during
intermediate
and
long-term
flooding
and
was
independent
of
CO,
concentration
over
the
ranges
studied
(Figs
2
and
3).
Changes
in
carbon
assimilation
due
to
ambient
CO,
concentration
were
associated
with
g',
for
unflooded
plants
at
all
stages
but
were
independent
of
g',
for
flooded
plants.
It
appears
that
flooding
has
a
rapid
(1-2
days)
effect
on
but
that
carboxylation
efficiency
is
also
limited,
particularly
after
long-term
flooding.
Da-
vies
and
Flore
(1985)
observed
similar
responses
during
short-term
flooding
of
rabbiteye
blueberry.
They
found
that
flooding
for
24
h
decreased
g',
and
g'„
again
sup-
porting
the
idea
that
carbon
assimilation
is
under
stom-
ata!
control
during
early
flooding.
Regehr
et
al.
(1975)
and
Phung
and
Knipling
(1976)
also
suggested
that
car-
bon
assimilation
is
controlled
primarily
by
g',
under
flooded
conditions.
Fig.
2.
Effects
of
CO,
concentration
on
carbon
assimilation
(A),
stomata]
conductance
to
CO,
(g',)
and
residual
conduct-
ance
(g',),
of
unflooded
and
flooded
Bluecrop
blueberry
plants.
Plants
were
flooded
for
10-14
days.
,
unflooded;
0,
flooded.
Effect
of
0,
concentration
on
carbon
assimilation
Carboxylation
efficiency
[mol
CO,
fixed
(mol
ambient
CO,)
-
']
of
flooded
plants
was
less
than
that
of
unflooded
plants
as
indicated
in
Figs
1-3,
and
influenced
differ-
ently
by
low
0,
levels
(Fig.
4).
Carbon
assimilation
and
response
to
varying
CO,
concentrations
(slope
of
the
line)
were
greater
for
unflooded
than
flooded
plants
at
10%
OF
21%
OF
10%
F
2%
F
21%
F
100
200
300
400
CCO2301
111-1
)
Fig.
4.
Effects
of
CO
2
and
0
2
concentrations
on
carbon
assimi-
lation
of
unflooded
and
flooded Bluecrop
blueberry
plants.
Linear
regression
equations:
21%
0
2
unflooded
y
=
-0.82
+
0.012x
r
2
=
0.94,
flooded
y
=
-0.93
+
0.004x
r
2
=
0.98;
10%
0,
unflooded
y
=
-0.67
+
0.016x
r
2
=
0.96,
flooded
y
=
-0.16
+
0.005x
r
2
=
0.98;
2%
0,
unflooded
y
=
-1.54
+
0.021x
r
2
=
0.98,
flooded
y
=
-0.31
+
0.005x
r
2
=
0.81,
F,
flooded;
UF,
unflooded.
6.0
-
2%UF
5.0
-
4.0
-
7
3.0
-
E
12.0
1.0
-
-1.0
548
Physiol.
Plant.
67,
1986
all
0,
concentrations.
Moreover,
a
reduction
in
the
con-
centration
of
0,
from
21
to
2%
increased
carbon
assimi-
lation
of
unflooded
plants
by
33%
at
330
µI
CO
2
1
-1
.
The
carboxylation
effiency
also
increased
from
0.012
mol
CO,
fixed
(mol
of
CO
2
)
-
'
at
21%
0
2
to
0.021
at
2%.
In
contrast,
although
carbon
assimilation
of
flooded
plants
increased
substantially
as
percentage
0
2
decreased,
the
slopes
of
the
CO,
response
curves
were
similar
and
low
at
all
0,
concentrations.
Carbon
dioxide
compensation
point
changed
very
little
for
unflooded
plants
(40-80
µI
1
-
'),
but
was
signifi-
cantly
reduced
for
flooded
plants
under
low
0
2
condi-
tions
from
232
(21%
0
2
)
to
20
(2%
0
2
).
Changes
in
0
2
concentration
affected
carbon
assimilation
through
changes
in
g',
not
g',.
This
situation
would
be
expected
since
0
2
is
a
competitive
inhibitor
of
CO
2
for
RuBP
car-
boxylase:
oxygenase.
The
response
to
low
0,
is
similar
to
that
reported
for
other
C,
plants
(Brown
1976).
Moreover,
the
rate
of
change
in
carbon
assimilation
per
unit
0,
(-0.117)
is
within
the
range
of
values
reported
by
Brown
(1976).
Carbon
dioxide
compensation
points
are
typical
of
other
C,
plants
and
much
greater
than
those
of
C
4
plants
(Orgen
1976).
Apparent
quantum
yield
Apparent
quantum
yield
was
significantly
less
for
flooded
than
unflooded
plants
at
all
flooding
durations
and
continued
to
decrease
with
flooding
duration
(Tab.
1).
Similarly,
Davies
and
Fiore
(1985)
observed
that
flooding
decreased
apparent
quantum
yield
of
rabbiteye
blueberry
plants.
The
reduction
in
apparent
quantum
yield
appears
to
be
a
function
of
decreases
in
g',
and
g',.
Apparent
quantum
yield
of
unflooded
plants
also
de-
creased
during
the
study,
possibly
because
plants
had
Tab.
1.
Effects
of
various
flooding
durations
on
apparent
quan-
tum
yield
of
Bluecrop
highbush
blueberry
plants.
Apparent
quantum
yield
values
are
calculated
as
the
slope
of
the
linear
portion
(50-300
Imot
nr
2
s
-
')
of
light
response
curves.
Carbon
assimilation
was
measured
at
50,
100,
180
and
300
µmot
m's
'
for
2
unflooded
and
flooded
plants
at
each
flooding
duration.
Calculated
light
compensation
points
represent
the
y
intercept
of
linear
regression
equations,
while
experimental
values
(exp.)
represent
those
observed
in
the
laboratory.
Flooding
duration
Treatment
Days
Light
comp.
pi
Apparent
quantum
yield
(umol
m
=
s
-
')
Exp.
Calc.
mol
CO,
(mol
Unflooded
1-2
25
0.06
0.22
0.81
Flooded
26
-0.52
0.12
0.36
Unflooded
10-14
25
0.16
0.16
0.88
Flooded
80
-0.26
0.002
0.86
Unflooded
35-40
35
-1.24
0.13
0.99
Flooded
102
-0.06
0.0009
0.71
acclimated
to
lower
light
levels
in
the
laboratory
during
the
incubation
period.
Nevertheless,
the
magnitude
of
carbon
assimilation
and
slope
of
CO
2
response
curves
for
flooded
plants
were
consistently
less
than
those
of
unflooded
plants.
Apparent
quantum
yields
for
highbush
blueberries
are
similar
to
those
calculated
from
studies
by
Teramura
et
al.
(1979)
for
rabbiteye
blueberries
and
Moon
et
al.
(1984)
for
highbush
blueberries.
However,
values
are
considerably
lower
for
highbush
blueberry
than
those
of
peach
(0.30;
DeJong,
1983),
or
citrus
(0.29;
Sybertsen
1984).
Calculated
light
compensation
points
are
unreal-
istically
low
because
they
are
based
on
best-fit
linear
re-
gressions.
However,
observed
light
compensation
points
ranged
from
25-35
umol
m'
s'
for
unflooded
plants
to
80-102
for
plants
flooded
more
than
10
days.
Carbon
assimilation
is
one
half
to
one
third
of
that
observed
for
apple
(Avery
1977),
sour
cherry
(Sams
and
Fiore
1982)
or
peach
(Byers
et
al.
1984)
and
is
also
lower
than
that
reported
previously
for
highbush
blue-
berries
(Moon
et
al.
1984).
Light
levels
during
devel-
opment
in
the
greenhouse
and
laboratory
were
lower
in
our
study,
which
may
account
for
lower
carbon
assimila-
tion
levels.
Hydraulic
conductivity
of
the
root
Root
conductivity
expressed
on
a
root
weight
basis
was
lower
for
flooded
plants
within
1-2
days
of
flooding
and
continued
to
decrease
to
low
levels
after
long-term
flooding
(Tab.
2).
Studies
by
Syvertsen
et
al.
(1983)
for
citrus
also
showed
decreases
in
root
hydraulic
conduc-
tivity
for
flooded
plants
within
3
days.
Leaf
water
poten-
tial
in
this
study
did
not
differ
between
unflooded
and
flooded
plants
during
short-
or
intermediate-term
flood-
ing.
Leaf
water
potential,
however,
averaged
-0.86
and
-1.52
MPa
for
unflooded
and
flooded
leaves,
respec-
tively,
after
long-term
(35-40
days)
flooding.
In
con-
trast,
leaf
water
potential
generally
remained
un-
changed
during
flooding
in
other
plant
species
(Periera
and
Kozlowski
1977,
Davies
and
Wilcox
1984,
Pezeshki
and
Chambers
1985).
Highbush
blueberry
grows
poorly
under
flooded
con-
ditions
in
the
field
(Kender
and
Brightwell
1966),
how-
ever,
it
is
flooding
tolerant
under
controlled
conditions
Tab.
2.
The
effect
of
various
flooding
durations
on
root
hy-
draulic
conductivity
I(cm'
H,0
11
-4
MPa'
(g
root
DW)
-
'I
of
Bluecrop
highbush
blueberry.
Each
value
represents
the
mean
of
2
unflooded
and
2
flooded
plants/duration
±
SD.
Flooding
duration
Root
hydraulic
conductivity
(days)
Unflooded
Flooded
1-2
0.016±0.003
0.007±0.001
10-14
0.006±0.001
0.004±0.002
35-40
0.005±0.002
0.001
±0.001
Physiol.
Plant.
67,
1986
549
if
Phytophthora
root
rot
is
not
a
problem
(Abbott
and
Gough
1985,
Davies
and
Flore
1986).
Previous
studies
indicate
that
g,
and
transpiration
are
affected
within
4-5
days
of
flooding
(Davies
and
Wilcox
1984).
However,
studies
with
rabbiteye
blueberry
(Davies
and
Flore
1986),
citrus
(Phung
and
Knipling
1976)
and
Liqui-
dambar
(Pezeshki
and
Chambers
1984)
indicate
effects
on
gas
exchange
within
24
h.
It
appears
that
root
hy-
draulic
conductivity
is
significantly
reduced
within
1-2
days
of
flooding,
which
directly
or
indirectly
causes
de-
creased
g,
and
transpiration.
Such
a
mechanism
would
limit
transpirational
losses
(Coutts
1981).
This
mecha-
nism
also
leads
both
to
reduced
carbon
assimilation
and
starch
accumulation
(Wample
and
Thornton
1984).
Other
studies
indicate
that
carbon
assimilation
of
high-
bush
blueberry
becomes
negative
after
10-14
days
of
flooding,
particularly
at
temperatures
above
28°C
(Da-
vies
and
Flore
1986),
suggesting
that
highbush
blue-
berry
does
not
adapt
to
flooded
conditions
as
observed
for
Populus
(Periera
and
Kozlowski
1977)
and
Liqui-
dambar
styraciflua
(Pezeshki
and
Chambers
1985).
Therefore
highbush
blueberry
is
physiologically
intol-
erant
to
flooding
and
appears
to
survive
prolonged
flooding
via
stomata]
closure
rather
than
through
mor-
phological
or
anatomical
adaptations,
as
observed
in
other
plants
(Periera
and
Kozlowski
1977,
Wenkert
1981).
Acknowledgement.
-
We
thank
J.
Hancock
for
his
help
in
ob-
taining
and
growing
plant
material.
Michigan
Agr.
Expt.
Sta.
Jour.
Article
No.
11674.
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R.
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1985.
Effects
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gas
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Gas
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1984.
Waterlogging
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1977.
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