A broad survey on hydraulic and mechanical safety in the xylem of conifers.
Pauline Bouche, Maximilien Larter, Jean-Christophe Domec, Régis Burlett, Peter Gasson, Steven Jansen, Sylvain Delzon
Pittermann et al. 2010
High variability between genera Evolution
Delzon et al. 2010
Funtional and evolutionary role of torus margo pits in conifers
Objectives
1- Better understand mechanism of cavitation in conifers
2- What are the consequences of increasing cavitation resistance? Hydraulic safety
Hydraulic efficiency mechanical safety
a)Trade-off hydraulic vs. Mechanical safety?
b)Trade-off hydraulic safety vs. efficiency?
Materials and methods Bordered pit properties
Tracheid properties
Anatomical database : 115 species
-Relationships
Cavitation database : 236 species
- Phylogenetic analyses
Cavitation Air-seeeding in angiosperms Rupture of meniscus => Air-seeding Ψ=0 MPa
Ψ =-2,5 MPa
Ψ=0 MPa
Ψ=0 MPa
Pit membrane of Populus fremontii Jansen et al. (2009)
Hacke et al. (2004)
What about conifers? torus Rupture of air-sap meniscus Ψ=0 MPa
Ψ=-1 MPa
=> Air-seeding
Cochard et al. (2009)
Cavitation Air-seeeding in angiosperms Rupture of meniscus => Air-seeding Ψ=0 MPa
Ψ =-2,5 MPa
Ψ=0 MPa
Ψ=0 MPa
Pit membrane of Populus fremontii Jansen et al. (2009)
Hacke et al. (2004)
What about conifers? torus
Cochard (2006)
Part 1: Mechanism of cavitation in conifers
Cochard et al. (2009) Delzon et al. (2010)
Part 1: Mechanism of cavitation in conifers
H1 Magic air-seeding Cochard et al. 2006
Cochard et al. (2009) Delzon et al. (2010)
H2 Seal capillary-seeding Delzon et al. 2010
H3 Torus capillary-seeding Jansen et al. 2012
Part 1: Mechanism of cavitation in conifers
H1 Magic air-seeding Cochard et al. 2006
Cochard et al. (2009) Delzon et al. (2010)
H2 Seal capillary-seeding Delzon et al. 2010
H3 Torus capillary-seeding Jansen et al. 2012
Part 1: Mechanism of cavitation in conifers C)
Torusoverlap overlap Torus
0.6
s = 0.46 , p < 0.0001
0.06
12
2
20
P50 (-MPa)
Seal capillary-seeding = most likely hypothesis Convergent evolution Overlap = best proxy of cavitation resistance
Part 1: Mechanism of cavitation in conifers Family
Punctured torus species/total species*
Araucariaceae Cephalotaxaeae
1/3
Cupressaceae
3/32
Pinaceae
15/17
Podocarpaceae
0/15
Sciadopityaceae
0/1
Taxaceae
0/4
Total
Torus capillary-seeding Torus capillary-seeding pressure (-MPa) pressure (-MPa)
-
19/72
s = 0.52, p = 0.046 8
Seal capillary-seeding = most likely hypothesis
Except for Pinaceae 4 2
4
(-MPa) PP5050 (-MPa)
6
8
Torus capillary-seeding
Part 2- Trade-offs : hydraulic vs. mechanical safety How mechanical properties of xylem conduits alter cavitation resistance?
-Cavitation-induced embolism associated with high mechanical constraint TW
Strong tracheid needed -Thickness to span ratio TW/DT
DT
Sperry et al. (2006)
Constant wall thickness to reduce carbon investment
Part 2- Trade-offs : hydraulic vs. mechanical safety B)
a)
Diameter
r = - 0.3 , p = 0.008
10 10
r = 0.41 , p = 0.0003
Thickness
r = 0.58 , p < 0.0001
0.1 1.5
15
P50 (-MPa)
0.1 0.1
0.4
11
Thickness to span ratio
-Indirect trade-off: High cavitation resistance = high mechanical resistance = carbon cost - Maintain a minimum level of hydraulic conductance
Wall thickness or Lumen diameter (µm)
Thickness to span ratio
0.5
Part 2- Trade-offs : hydraulic vs. mechanical safety Sperry et al. (2006) Diameter
r = - 0.3 , p = 0.008
10 10
Thickness
r = 0.58 , p < 0.0001
0.1 0.1
0.4
11
Thickness to span ratio
-Indirect trade-off: High cavitation resistance = high mechanical resistance = carbon cost - Maintain a minimum level of hydraulic conductance
Wall thickness or Lumen diameter (µm)
B)
Part 3- Trade-offs hydraulic safety vs. efficiency Specific hydrualic conductance (m² MPa -1 s-1)
0.003 0.0025
No trade-off between hydraulic safety and efficiency Delzon et al. Unpublished data
0.002 0.0015 0.001
Confirmed by anatomical investigations ?
0.0005 0 0
5
10
P50 (MPa)
15
20
Part 3- Trade-offs hydraulic safety vs. efficiency Specific hydrualic conductance (m² MPa -1 s-1)
0.003 0.0025
No trade-off between hydraulic safety and efficiency Delzon et al. Unpublished data
0.002 0.0015 0.001
Confirmed by anatomical investigations ?
0.0005 0 0
5
10
15
20
10 0.0001
0.001
kS (m²
MPa-1 s-1)
- No impact of conduit size
Margo pores diameter (µm)
Lumen diameter (µm)
Pit aperture diameter (µm)
P50 (MPa)
2 0.0001
0.001
kS (m²
MPa-1 s-1)
1
0.1 0.0001
0.001
kS (m²
MPa-1 s-1)
- Trade-off at pit membrane level?
Conclusion boreal
temperate
tropical
0.45
Seal capillary-seeding: most likely hypothesis Overlap
Overlap = best proxy of cavitation resistance strong evolutionary correlation
b
0.4 0.35
a a
0.3 0.25 0.2
mediterranean
a
Conclusion boreal
temperate
tropical
0.45
Seal capillary-seeding: most likely hypothesis Overlap
Overlap = best proxy of cavitation resistance strong evolutionary correlation
Maintain of a minimum lumen diameter
a a
0.3 0.25 0.2
Cavitation resistance and thickness to span ratio Indirect link to resist to mechanical stress
b
0.4 0.35
mediterranean
a
Conclusion boreal
temperate
tropical
mediterranean
0.45
Seal capillary-seeding: most likely hypothesis
0.4
Overlap
Overlap = best proxy of cavitation resistance strong evolutionary correlation
b
0.35
a a
0.3
a
0.25 0.2
Cavitation resistance and thickness to span ratio Indirect link to resist to mechanical stress Maintain of a minimum hydraulic conductance
consistant with lack of trade-off at conduit level Trade-off between cavitation resistance and hydraulic efficiency at pit level?
Estimation of the total hydraulic resistivity
A broad survey of hydraulic and mechanical safety in the xylem of conifers Pauline Bouche, Maximilien Larter, Jean-Christophe Domec, Régis Burlett, Peter Gasson, Steven Jansen, Sylvain Delzon
Thanks for your attention
13
Thanks for your attention
1- … and trade-off(s)
DT
a)
B)
r = - 0.3 , p = 0.008
10 10
r = 0.58 , p < 0.0001
r = 0.41 , p = 0.0003 0.1 1.5
15
0.1 0.1
0.4
11
Wall thickness or Lumen diameter (µm)
TW
Thickness to span ratio
0.5
Thickness to span ratio
P50 (-MPa)
- Maintain a minimum level of hydraulic conductance
- Collapse unlikely in xylem of branch
Wall implosion pressure (-MPa)
- Trade-off : Construction cost of a safe xylem C) 20
r = 0.51 , p < 0.0001 2
1.5 1.5
15 15
P50 (-MPa)
