presentation: transpiration during avocado flowering: how
TRANSCRIPT
Transpiration during avocado flowering: How much water do
the flowers use?
Mike Clearwater, Sam Ong, Mary Black, Bill
Snelgar, Peter Minchin
1
Water stress during flowering?• What are the causes of alternate bearing?
• Does water stress contribute to poor fruit set?
• “Flowers use 80% of the water”
• Pollen tube growth is sensitive to water potential
2
Previous studiesWhiley et al. (1988)
• Inflorescences increase canopy surface area of ‘Fuerte’ by 90%
• Estimated that flowers add 13% to tree transpiration
Blanke and Lovatt (1993)
• Compared the surface morphology and transpiration of leaves and flowers
• No estimates of total water use
Our hypothesis:
• Inflorescences add significantly to tree transpiration, leading to
soil moisture deficits and plant water stress
3
Methods• Hass Avocado in the Bay of Plenty, New Zealand
• Flower and leaf removal from whole trees and branches
• Measured - inflorescence and leaf area- inflorescence and leaf stomatal conductance- tree and branch transpiration using sap flow
- soil moisture, water potentials, photosynthesis
• Compared transpiration estimated from surface area and
conductance with transpiration measured using sap flow
4
Measuring inflorescence surface area
5
• Fluidized bed of ‘Ballotini beads’
• Dip in glue – weigh – dip in beads – reweigh
• Area = change in weight added by coating of glass beads
y = 18.84xR² = 0.94
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
Inflo
rescence s
urf
ace
are
a (c
m2)
Inflorescence fresh weight (g)
Inflorescence surface area correlated
with fresh weight
6
0
0.1
0.2
0.3
0.4
0.5
0.6
Infl
ore
sce
nce
are
a /
To
tal a
rea
One-sided
inflorescence area
Total
inflorescence area
Inflorescence area as a proportion of total
surface area
7
Measuring stomatal conductance
• Stomatal conductance was measured using a gas exchange
system
• Response to humidity was measured as an indicator of the
level of stomatal control over transpiration
8
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.5 1.5 2.5 3.5
Sto
mata
l conducta
nce (
molm
-2s
-1)
Vapour Pressure Deficit (kPa)
leaves
inflorescences
Stomatal response to humidity
9
Low humidity
High temperature
High humidity
Low temperature
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0.5 1.5 2.5 3.5
Tra
nspiration (
molm
-2s
-1)
Vapour Pressure Deficit (kPa)
leaves
inflorescences
Transpiration response to humidity
10
Low humidity
High temperature
High humidity
Low temperature
Measuring transpiration in the field
11Paired branches, deflowering and deleafing
Heat pulse sap flow probes
Transpiration from sap flow
12
0
2
4
6
8
10
300 305 310 315 320
Tra
nspiration (
L h
our-
1)
Day of the year
tree 1tree 2
Tree 2 deflowered
Tree 1 deleafed
13
0
2
4
6
8
10
300 305 310 315 320
Tra
nspiration (
L h
our-
1)
Day of the year
tree 1tree 2
Tree 2 deflowered
Tree 1 deleafed
0
0.5
1
1.5
2
300 305 310 315 320
Ratio (
Tre
e 1
/ T
ree 2
)
Day of the year
De-flowering = 8% reduction in transpiration
De-leafing = 78% reduction in transpiration
Comparison – Area vs Transpiration
14
y = 0.53x0
0.04
0.08
0.12
0.16
0.2
0.1 0.2 0.3 0.4
Infl. T
ransp.
/ Tota
l T
ransp.
Infloresecence area / Total area
Soil moisture and plant water potentials
• Experiment conducted under mild conditions with adequate
rainfall
• No significant decline in soil water content over flowering
• Plant water potentials and stomatal conductance were unaffected by flower removal, even with heavy flowering
15
Conclusions• Inflorescences contribute up to 35% of the total transpirational
surface area during flowering
• Inflorescence surface conductance is half or less that of
leaves
• Inflorescences contribute up to 15% of the total transpirational
water loss during flowering
• The flowers do not use 80% of the water, but soil moisture
and irrigation management still matter
• Soil moisture deficits and tree water stress are unlikely to
contribute to alternate bearing if carefully managed
• Flower water relations may still be a factor in fruit set
16
Acknowledgements
NZ Avocado Industry Council
Jonathan Dixon
NZ Foundation for Research, Science and Technology
Mike Clearwater
17