new insights into the hydraulics of trees hervé cochard umr547 piaf inra clermont-ferrand france

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New insights into New insights into the hydraulics of the hydraulics of trees trees Hervé Cochard Hervé Cochard UMR547 PIAF UMR547 PIAF INRA INRA Clermont-Ferrand France Clermont-Ferrand France

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Page 1: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

New insights into the New insights into the hydraulics of treeshydraulics of trees

New insights into the New insights into the hydraulics of treeshydraulics of trees

Hervé CochardHervé Cochard

UMR547 PIAFUMR547 PIAFINRAINRA

Clermont-Ferrand FranceClermont-Ferrand France

Page 2: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Drought resistance is a major issue for European forests

- Extreme drought events during the recent decades (1976, 1990, 2003)

- Severe forest diebacks across Europe

- The occurrence of extreme droughts is thought to increase in the future (global climate change)

How sustainable are our forests ?

Page 3: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

NOW

2050 2100

Frequency distribution

Distribution of drought resistant species in France for the next century

Quercus ilex

Badeau and Dupouey 2005

Page 4: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

NOW

2050 2100

Frequency distribution

Distribution of drought vulnerable species in France for the next century

Fagus sylvatica

Badeau and Dupouey 2005

Page 5: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Challenging issues from foresters (and researchers)

- Adopt now new cultural practices ?

- Can current species acclimate/adapt to drier conditions ?

- Can we identify genotype/ecotype of current species more resistant to drought ?

- Can we substitute current species with more drought resistant ones ?

Better understanding of the physiological and molecular basis of tree drought resistance

Page 6: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Su

rvival

Gro

wth

Stom

atal Conductance

Ph

oto

synth

esis0

20

40

60

80

100

Inte

nsit

y of

the

proc

esse

s

Time / Drought Intensity

Tree drought «resistance »

Xyl

em C

avit

atio

n

Hyd

raul

ic R

esist

ance

↑ Productivity ↑ Resilience

Hydraulic traits may provide new insights into our understanding of tree drought resistance

Page 7: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The Hydraulic behavior The Hydraulic behavior of treesof trees

The Hydraulic behavior The Hydraulic behavior of treesof trees

Page 8: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The ‘Hydraulic’ behavior of trees

Hours

0 6 12 18 24

le

af

, MP

a

-3

-2

-1

0

Sa

p F

low

De

ns

ity

dm

3 d

m-3

h-1

0.0

0.5

1.0

1.5vp

d, h

Pa

0

5

10

15

20

Rg

, Wm

-2

0

200

400

600

800

1000

P

TSap flow density, dm3 dm-2 h-1

0.0 0.5 1.0 1.5 2.0

le

af ,

MP

a

-3

-2

-1

0

= – RH*Flow

Ohm’s law analog for water transport in trees

RH=1/KH

Cochard et al 1997

Page 9: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The hydraulic limit of sap transport: Cavitation

Water nucleation (cavitation) can occur under negative pressure

Sap is transported in xylem conduits under large negative pressures

Air-seeding process

Page 10: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Trees operate close to the point of xylem cavitation

Per

cent

Xyl

em C

avit

atio

n

Sto

mat

al c

ondu

ctan

ce

Xylem Pressure, MPa

Page 11: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Epicéa

-5 -4 -3 -2 -1 0

0

20

40

60

80

100

Mais

-5 -4 -3 -2 -1 0

Noyer

-5 -4 -3 -2 -1 0

PL

C

0

20

40

60

80

100

Chêne

Potentiel hydrique-5 -4 -3 -2 -1 0

‘Stomatal control of xylem cavitation’

Epicéa

-5 -4 -3 -2 -1 0

0

20

40

60

80

100

Mais

-5 -4 -3 -2 -1 0

0.0

0.2

0.4

0.6

0.8

1.0

Noyer

-5 -4 -3 -2 -1 0

PL

C

0

20

40

60

80

100

Chêne

Potentiel hydrique-5 -4 -3 -2 -1 0

Con

duct

ance

sto

mat

ique

/ T

rans

pira

tion

rela

tive

0.0

0.2

0.4

0.6

0.8

% C

avit

atio

n

Stom

atal

con

duct

ance

Xylem Pressure, MPa induisant 10% d'embolie, MPa

-6 -5 -4 -3 -2 -1 0

in

duis

ant 9

0% d

e fe

rmet

ure

stom

atiq

ue

-5

-4

-3

-2

-1

0

QR

QP

PA

FS

PTJR

CA

CL

CLCBCS

PH

CS

CA

VMZM

Provoking 10 % embolism

P

rovo

king

90

% s

tom

atal

clo

sure

Cruiziat, Cochard, Améglio 2002

Page 12: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Populus cv ‘ peace ’

Experimental evidence for a stomatal control of cavitation

Cochard, Ridolfi, Dreyer 1996

Perc

ent C

avit

atio

n

Distance to apex, cm

Page 13: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Sap flow density, dm3 dm-2 h-1

0.0 0.5 1.0 1.5 2.0

le

af ,

MPa

-3

-2

-1

0

RH=1/KH

CAVITATION

Hydraulic traits with high functional significance

More efficient

Safer

Page 14: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The significance of The significance of hydraulic efficiency for hydraulic efficiency for

treestrees

The significance of The significance of hydraulic efficiency for hydraulic efficiency for

treestrees

Page 15: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Brodribb et al, 2007

How significant is the hydraulic efficiency for trees ?

Plant Hydraulic Conductance

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Rel

ativ

e T

rans

pira

tion

0.0

0.2

0.4

0.6

0.8

1.0

1.2

ChillingPressurizationDrought

Cochard et al, 2002

Walnut BryophytesFernsConifersAngiosperms

Hydraulic efficiency scales with leaf gas exchanges

Page 16: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Where are the located the main hydraulic resistances along the sap pathways ?

Veins ≈ 10-50% of leaf Resistance

Cochard et al, 2004 Root Resistance ≈ Shoot Resistance

Résistance Hydraulique, %0 20 40 60 80 100

C. atlanticaC. libani

Q. ilexQ. petraea

Q. roburF. sylvatica

P. persicaP. malusS. fragils

B. verrucosaJ. regia

F. exelsior

Tiges Feuilles

Leaves ≈ 80% of shoot Resistance

Page 17: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Sap pathways in leaves

ApoplasmicMesopyll cell wall

SymplasmicMesopyll cell symplasm

GaseousEvaporation in

stomatal chambers

Page 18: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Temperature, °C

0 10 20 30 40

Kle

af,

0

5

10

15

20

Leaf conductance is variable and under environmental control

PAR

0 500 1000 1500 2000

Kle

af,

10

15

20

25

Cochard et al 2007Nardini, unpublished

Page 19: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Leaf conductance can vary rapidly

Cochard et al 2007

Sack et al (2002) : light decreases leaf hydraulic resistance

A variable Symplasmicpathway

Page 20: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Tajkhorshid et al 2002Cochard et al 2007

Molecular basis of variable leaf conductance :

Aquaporins

Page 21: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

- Aquaporins

Cochard et al 2007

+Aquaporins

Functional significance of leaf aquaporins

Page 22: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Querc

us ro

bur

Betula

Fagus

Robini

a

Fraxin

usAce

rAlnu

s

Populu

s delt

oides

Populu

s tre

mula

Populu

s X

Salix

alba

Kle

af

0

5

10

15

20

25

DarkLight

Aquaporins do not transport only H20 “CO2-porins” Uehlein et al 2003 Control CO2 diffusion in the leaf mesophyll (photosynthesis)

Future issues for aquaporins and leaf

hydraulics

Great diversity of leaf response to light

Great diversity of aquaporins

unpublished

Page 23: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Hydraulic efficiency

• Key parameter• Correlates tightly with gas exchanges• Highly variable across species• Highly sensible to environmental factors• Under biological control : Aquaporins

Hydraulic conductances are tightly regulated to optimized leaf gas exchanges

Page 24: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The significance of The significance of xylem cavitation for xylem cavitation for

treestrees

The significance of The significance of xylem cavitation for xylem cavitation for

treestrees

Page 25: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Xylem pressure, MPa0-2-4-6-8-10-12

% X

ylem

cav

itat

ion

Populus

Quercus robur

Pinus

Prunus

JuniperusBuxus

Xylem vulnerability to cavitation across species

Page 26: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Xylem pressure inducing 50% cavitation, MPa-8 -7 -6 -5 -4 -3 -2 -1 0

Buxus sempervirensTaxus baccataCrataegus monogynaPrunus spinosaAmelanchier ovalisPinus HalepensisQuercus ilexLonicera etruscaQuercus suberPinus corsicanaCedrus atlanticaEuonymus europaeusCarpinus betulusPinus mughoAbies albaPinus pinasterPicea abiesCytisus scopariusPseudotsugaQuercus petraeaPinus cembraPinus sylvestrisFagus sylvaticaPopulus nigraFraxinus excelsiorQuercus roburPinus nigraPopulus tremulaQuercus rubraBetula pendulaSalix capreaJuglans regiaSalix capreaAlnus glutinosaPopulus albaPopulus trichocarpaSalix fragilisPopulus euphratica

HygrophilousMesophilousXerophilous

Maherali et al 2004

Cavitation resistance correlates with species ecological preferences

Page 27: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Cochard et al 2007

Cavitation resistance across Prunus species

Page 28: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Salges

ch, S

w

Vallce

bre,

Sp

Prades

, Sp

Fontfr

eyde

, Fr

Granad

a, Sp

Jeizi

nen,

Sw

Potenz

a, It

Leuve

numse

, Nl

Scotla

nd

Kootw

ijk, N

l

Hyytia

la,Fi

P50,

MPa

-4.0

-3.5

-3.0

Pinus sylvestris

Cochard et al unpublished

Page 29: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Cavitation resistance seems an adaptive trait for drought resistance

How cavitation could cause tree dieback ?(Still speculative)

Direct effects in the short term:- ‘run-away cavitation’- bud and meristem mortality by dehydration

Indirect effects in the longer term:- lower carbohydrate reserves

(frost resistance; bud growth)- Impair impairment by loss of hydraulic conductance (less competitive)

Can ‘cavitation resistance’ be used as a criterion for screening more drought-resistent genotypes ?

Page 30: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Intrinsic, structural property of the xylem

• Do we have fast and reliable techniques for screening hundred of genotypes ?

• Can we identify more accessible traits correlated with cavitation resistance ?

• Can we identify genes involved in cavitation resistance ?

Screening cavitation-resistant genotypes

Page 31: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Techniques for measuring cavitation

www.bronkhorst.fr

XYL’EM

Loss of hydraulic conductance (Sperry et al 1988) :

Reliable but not fast (1genotype/week)

Acoustic emissions (Tyree et al 1985)

Not reliable and not fast

Page 32: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Techniques for measuring cavitation

Air injection(eg, Cochard et al 1992)

Rather Fast , reliable ?(1genotype/day)

0r0.5

1

Centrifuge technique(Cochard et al 2005)

Very fast, reliable ?(5 genotypes/day)

Page 33: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Betula

Prunus

Quercus

PLC

20

40

60

80

100

PLC

20

40

60

80

100

17.5 cm water27.5 cm water37.5 cm water

Xylem Pressure, MPa-6 -5 -4 -3 -2 -1 0

PLC

0

20

40

60

80

100

Evaluation of the ‘cavitron’ technique

With this technique about 5 genotypes/day.More accessible traits ?

Max vessel length

3 different sample length

‘true curve’ 15 cm

30 cm

140 cm

Reliable for conifers and species with short vessels

Page 34: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

P50, MPa

-7 -6 -5 -4 -3

Inte

r-ve

ssel

wal

l thi

ckne

ss

of la

rger

ves

sels

, µm

3.0

3.5

4.0

4.5

5.0

5.5

6.0P. padus

P. cerasus

P. avium

P. persica

P. spinosa

P. mahaleb

P. domestica

P. armeniaca

P. amygdalusP. cerasifera

Densité du bois, g cm-30.3 0.4 0.5 0.6 0.7 0.8

Ten

sion

de

sève

, MP

a in

duis

ant 5

0% d

'em

boli

e

-8

-7

-6

-5

-4

-3

-2

-1

Wood density

P50,

MP

aAnatomical traits correlated with cavitation across species

Hacke et al 2001

Page 35: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

P50, MPa

-2.4 -2.2 -2.0 -1.8 -1.6 -1.4

Inte

r-ve

ssel

wal

l thi

ckne

ss, µ

m

2

3

4

5

6

Poplar clonesSalix clones

P50, MPa

-2.4 -2.2 -2.0 -1.8 -1.6 -1.4

Woo

d de

nsity

, kg

dm-3

0.30

0.35

0.40

0.45

0.50

Poplar clonesSalix clones

Anatomical traits do not seem to correlate with cavitation across genotypes

Cochard et al 2007

Page 36: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

The molecular basis of xylem cavitation ?

A better understanding of the mechanism of cavitation

Angiosperms

Conifers

P50

, MP

a

-6

-5

-4

-3

-2

-1

0

ControlTween 40Triton X100Merpol

PinusCedrus PiceaFagus

Cochard unpublished

Effect of water surface-tension on cavitation

Page 37: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Identify the structural/textural characteristics of pit membranes determining cavitation

Page 38: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

How to identify genes involved xylem cavitation ?

UPD-glucose dehydrogenase(UGHD).UPD-glucuronate 4-epimerase.Pectine methylesterase.Glycosyltransferase.

Glucosyltransferase.UPD-glucose pyrophosphorylase.

Cellulose synthase(CSL).

Boron + Boron -

Boron links in pectins

Manipulate plants

Screen mutant banks for specific genes coding for the primary cell wall (Arabidopsis)

Experimentally

Fagus sylvatica

Potentiel Hydrique, MPa

-5 -4 -3 -2 -1P

LC

0

20

40

60

80

100

Ombre

Lumière

shade

Full light

Global techniques cDNA-AFLP

Page 39: New insights into the hydraulics of trees Hervé Cochard UMR547 PIAF INRA Clermont-Ferrand France

Conclusion

Aquaporins Cavitation

- Two keys aspects of tree hydraulics- Physiological implications - Molecular basis- Ecological significance

- More drought performing forests