functionnal and ecological significance of cavitation in trees umr piaf inra-université blaise...
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Functionnal and ecological significance of cavitation in trees
UMR PIAFINRA-Université Blaise Pascal
Clermont-Ferrand
Louuvain, 7-02-2013
Hervé Cochard
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Salt & Water Stress in Plants
Newry August 2014
Cohesion-Tension Theory (Dixon 1896)
Hours
0 6 12 18 24
le
afle
t
, M
Pa
-3
-2
-1
0
Fd, d
m3 d
m-3 h-1
0.0
0.5
1.0
1.5
vp
d, h
Pa
0
5
10
15
20
Rg
, W
m-2
0
200
400
600
800
1000-a-
-b-
-c-
0
Pxy
lem
, M
Pa
Daily time course of xylem pressure
Ash trees
CAVITATION
Cavitation: a common phenomenon
Cavitation in trees? Positive? Negative?What is its biological significance?
% C
AV
ITA
TIO
N
Sap pressure, MPa
P50
Xylem vulnerability curves to cavitation
P50 = Sap pressure provoking 50% cavitation
Methods to measure cavitation
Acoustic Emissions Tyree et al 1985
Hydraulic conductance lossSperry et al 1988
Air injectionCochard et al 1992
0r0.5
1Centrifuge techniqueAlder et al 1997, Cochard 2002
Dehydration
How vulnerable are tree species to cavitation?
% c
avita
tion
Sto
mat
al C
ondu
ctan
ceMartin St Paul et al (in press)
Highly cavitation-resistant species
Sap pressure, MPa
Quercus ilex
Px-min
Sigmoidal curve
Jacobsen & Pratt 2012
Vitis
Zufferey, et al 2011%
cav
itatio
nS
ap p
ress
ure
, M
Pa
Low cavitation-resistance species
Sto
mat
al C
ondu
ctan
ce
% c
avita
tion
Px-min
Exponential curve
Sap pressure, MPa
Xylem pressure, MPa
-5 -4 -3 -2 -1 0
PL
C
0
20
40
60
80
100
ExponentialSigmoidal
Two ‘strategies’ for tree hydraulics
Sto
mat
al c
on
du
ctan
ce
% c
avita
tion
Sap pressure, MPa
Low cavitation-resistance:- Cavitation forms as soon as Px<0- Cavitation and repair are routine on
a daily basis- Water release by cavitation sustain
stomatal opening & carbon gain
High cavitation-resistance:- Cavitation forms when Px<Pcav
- Stomatal control of cavitation- Cavitation occurs only under intense
drought conditions- Refilling is seasonal
The same species have been found to display both strategies !!!
50/50
Cochard & Delzon 2013
What is the biological significance of cavitation ?
Px-min
Pitfalls in hydraulic methods ?
Xylem pressure, MPa
-5 -4 -3 -2 -1 0
PL
C
0
20
40
60
80
100
ExponentialSigmoidal
Air
deh
ydra
tion
Air
inje
ctio
nC
entr
ifuga
tion
Coniferous Diffuse-porous Ring-porous
Sigmoidal
Exponential
Sigmoidal Sigmoidal
Sigmoidal
Sigmoidal Exponential
ExponentialExponential
Sigmoidal
Literature survey > 1000 curves > 500 species
Cochard et al 2013
Open vessel artifact?Cochard et al 2010
Refilling artifactJacobsen et al 2012
Open vessel artifact?Ennajeh et al 2011
Ind
ire
ct a
nd
inva
sive
met
ho
ds
Need for a Reference technique : X-ray Tomography (HRCT)
Direct observation, non-invasive, non-destructive
High resolution (<1µm), measures density variations
Affordable laboratory systems now available(more invasive)
Experiments using synchrotron light and living trees
S Jansen
B ChoatS Delzon
E Badel
H CochardR Burlett
T Brodribb
Oak
HR-CT
Deh
ydra
tion
unpublished
-2.9 MPa -5.1 MPa-3.5 MPa
Cen
trifu
gatio
n
% c
avita
tion
Px-min
Air injection
% c
avita
tion
OliveSap pressure, -MPa
Torres et al (in press)
HR-CT Px-min
HR-CT
Laurel (Laurus nobilis)
Sap pressure, MPa
% c
avita
tion
Cochard et al (in press)
Px-min
?
Tension sample
Relaxed sample
Tension sample
Relaxed sample
But see Trifilo et al (in press)!
% c
avi
tatio
n
Xylem tension (MPa)
0,4 1,55 3 3,6 4,1
Deg
ree
of e
mbo
lism
(%
)
0
10
20
30
40
50
60
70
A. campestre E. pauciflora
Incr
emen
t of t
he d
egre
e of
em
bolis
m (
%)
0
10
20
30
40
IP CUT IP CUT IP CUT IP CUT IP CUT
b
a
E. pauciflora
- - - - - MPa
Intact
Cut under tension
Intact Cut under
tension
Cut under tensionIntact
unpublished
-3.6MPa
Eucalyptus potted plants
Cutting artifactWheeler et al
Refilling artifactTrifilo et al
% c
avi
tatio
n
Xylem pressure, MPa
-5 -4 -3 -2 -1 0
PL
C
0
20
40
60
80
100
ExponentialSigmoidal
% c
avita
tion
Sap pressure, MPa
Px-min
High cavitation-resistance strategy has been validated(Oak, Eucalypt, Laurel, Olive, Poplar, Acer, Pinus, Abies,Vitis, Pteris)
Low cavitation-resistance strategy still needs to be confirmed
What is the biological significance of cavitation in trees ?
?
Oak
Xylem Pressure, MPa
Sto
mat
al c
on
du
ctan
ce
Stomatal / Hydraulic Coordination
Cochard et al 1996
Xylem pressure, MPa
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
% c
avita
tion
0
10
20
30
40
50
60
70
Rel
ativ
e pl
ant w
ater
loss
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Maize
Wheat
Xylem Pressure, MPa
-6 -5 -4 -3 -2 -1 0
Lea
f ev
apor
atio
n ra
te
0
1
2
3
4
5
% C
avit
atio
n
0
20
40
60
80
100
Cochard 2002
Neghliz, Cochard & Martre unpublished
% C
avit
atio
n
“Stomatal control of cavitation”
Xylem pressure, MPa%
Cav
itat
ion
0-3-6
Sto
mat
al c
ond
uct
aceXerophilous species
0-3-6
Hygrophilous species
0-3-6
Mesophilous species
Sto
mat
al c
ond
uct
ace
Sto
mat
al c
ond
uct
ace
% C
avit
atio
n
% C
avit
atio
n
Xylem pressure, MPa
Xylem pressure, MPa
Stomatal / Hydraulic coordination across species
unpublished
Xylem pressure at 10% Cavitation, MPa
Xyl
em p
ress
ure
at 9
0%
sto
mat
al
clos
ure,
MP
a
Populus x cv ‘peace’
+ABA
-ABA
Cochard, Ridolfi, Dreyer 1996
% C
avita
tion
Distance to apex, cm
% C
avita
tion
Sto
mat
al
con
du
cta
nc
e
Xylem Pressure, MPa
Why trees do their best to avoid cavitation at the cost of less carbon uptake ?
Water-stress
Hydraulic failure kills trees under extreme drought conditions
Fagus sylvatica
Weeks after drought onset
0 2 4 6 8 10 12
% E
mbo
lism
0
20
40
60
80
100
% M
orta
lity
0
20
40
60
80
100
% Mortality% Embolism
Barigah et al 2013
% c
avita
tion
Dry till death experiment
Taux de cavitation
0 20 40 60 80 100
Tau
x d
e m
ort
alit
é
0
20
40
60
80
100
% Cavitation
% M
orta
lity
Critical cavitation level for mortality after extreme drought event:
50% cavitation Gymnosperms(Brodribb & Cochard 2010; Brodribb et al 2011)
90% cavitation Angiosperms(Ulri et al 2013, Barigah et al 2013)
Gymnosperms
Angiosperms
Cavitation can delay mortality
Hydraulic failure-induced mortality
Lethal xylem pressure, MPa
-12 -10 -8 -6 -4 -2 0
Xyl
em p
ress
ure
at 5
0 P
LC
, MP
a
-12
-10
-8
-6
-4
-2
0AngiospermsGymnosperms
Vul
nera
bilit
y to
cav
itatio
n, P
50 M
Pa
0
% C
avita
tion
0
50
100
Drought stress intensity
Decennial Seasonal No droughtCentennial
PcavP50P90<<0
Delzon & Cochard 2014
Sap pressure, MPa
Gymnosperms
Angiosperms
Pmin : Minimum field xylem pressure under drought conditions
Tree safety margin for hydraulic failure-induced mortality
Gymnosperms:Pmin-P50
Angiosperms:Pmin-P90
Safety margins are >0 but constant across forest biomes
Modified from Choat et al. Nature 2012
Global convergence in the vulnerability of forests to drought
Vulnérabilité à la cavitation P50, MPa
-8 -6 -4 -2 0
StipeBrachypodeMéliqueChiendent cRay-grassFlouvePhléoleDactyleFétuqueFromentalChiendent rVulpinBlé récitalMaïsRizPanicGlycérieRoseauBaldingère
Vulnérabilité des Poacées à la cavitation (P50, MPA)
Xerophilous
Mesophilous
Hygrophilous
Crops
Cochard, Picon-Cochard, unpublished
Cavitation resistance in Poaceae (grasses)
Vulnerability to cavitation, P50 MPa
Tixier et al 2013
% c
avita
tion
% c
avita
tion
% c
avita
tion
% c
avita
tion
S Herbette
Melzer et al 2008
Lens et al 2013
“Woody” Arabidopsis (soc1-6 ful7 mutants)
% c
avita
tion
Xylem Pressure (Pmin, MPa)
0
% F
unct
ion
inte
nsity
0
50
100
Cavitatio
n
Tran
spir
atio
nP
ho
tosy
nth
esis
Mo
rta
lity
Drought stress intensity
Decennial Seasonal No droughtCentennial
PcavP50P90<<0 Pmidday
Take-home-doggy-bag message
1. Cavitation and repair and not routine in trees (plants?)
2. Coordination between stomatal and hydraulic functions
3. Cavitation forms under intense drought conditions
4. Hydraulic failure can induce tree mortality under extreme drought conditions
5. There is a future for Arabidopsis (in plant hydraulics)
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