College of Forestry, Northwest A&F University, China Institute for Systematic Ecology and Botany, University of Ulm, Germany Recalcitrant vulnerability curve in

Hippophae rhamnoides:

methods of analysis and the concept of fiber bridges for

enhanced cavitation resistance

Jing Cai, Shan Li, Haixin Zhang, Shuoxin Zhang, Melvin Tyree Besse, France

13.05.2014

1.1 Recalcitrant vulnerability curve

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Single Weibull function

rmse = 5.9

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exp1)100(exp1cc

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rmse = 1.4

Dual Weibull function

0

20

40

60

80

100

0 1 2 3 4

Tension (MPa)

PLC

(%

)

0

20

40

60

80

100

0 1 2 3 4Tension (MPa)

PL

C (

%)

0

20

40

60

80

100

0 1 2 3 4

Tension (MPa)

PLC

(%

)

What conduits account for each curve? 0

20

40

60

80

100

0 1 2 3 4

Tension (MPa)

PLC

(%) β" W1

W2

1.2 Vulnerability curve analysis

2. Wood anatomy Vessel grouping hypothesis Solitary vessels-fiber tracheids

Higher level of vessel groupings-libriform fibers

pits between fiber tracheids

solitary vessels

pits between vessels and fiber tracheids

3.1 Vessel-tracheids hypothesis

!  Important role of fiber tracheids in water transport

!  Small lumen of fiber tracheids confers more resistance to cavitation 0

20

40

60

80

100

0 1 2 3 4

Tension (MPa)

PL

C (

%)

Vessels? W1

W2

Fiber tracheids?

β"

3.2 Induced embolism - dye injection

2 cm stem segments

flushed 50% embolism 95% embolism

2 staining time 15 min 30 min 1 hour 2 hours

1 1

3.2 Staining pattern and tempo

0 MPa

-2.1 MPa

-4.5 MPa

15 min 30 min 1 hour 2 hours

100µm

3.3 Stem segment hydraulics

!  Kmax for 2 cm segments in LPFM

!  Plug the vessels by silicon

!  Cut 0.5 mm coating surfaces, flush and remeasure Kmax.

After silicone injection, Kh only accounts for 1.3% of the initial Kmax!

Expectation: fiber tracheids carry half of the whole stem hydraulic conductivity.

Hagen-Poiseuille law

Why did the fiber tracheids acquire the dye so rapidly? Fiber bridge between adjacent vessels? How is the hydraulic resistance of fiber bridges compared with vessel lumen?

The average sap velocity (v):

dxdPr

vη8

2

=

4.1 Introduction of fiber bridge

η = the viscosity of water, dP/dx=pressure gradient

As rv/rf =5, the dye in the fiber tracheids should move 0.04 times as the rate in the average vessel, but it appeared in fiber tracheids within 15 min!

possible water passway by one fiber bridge

4.1 Fiber bridge model

V

V

fiber bridge model

Hydraulic resistance comparison Rfb = Lf/(0.5Lv*EFK), where EFK is equivalent fiber bridge conductance, and where Rf is an average fiber hydraulic resistance and Ni is the number of fibers in a each bridge. Rvl = 0.5Lv/Kv, where Lv=average vessel length, Kv=conductivity of one vessel catena. Fiber bridge resistance is only 1/9 of the vessel lumen resistance of an average vessel!

∑=bridges Ni

1R f

1EFK F

4.2 Fiber bridge safety

Rvl is about 4 Rfb!

possible connections between fiber tracheids & vesselsdashed curve: hydraulic resistance of each vessel length class weighed by

probability distribution function (PDF) of vessel lengths; solid curve: hydraulic resistance of fiber bridge with each vessel length class weighed by PDF of vessel lengths.

fiber bridge resistance

vessel lumen resistance

5. Tentative proposal

The first Weibull may be associated with vessels connected directly by pit

fields, as the P1/2 of the first Weibull curve is about -0.9 MPa in H. rhamnoides, which is similar to hybrid cottonwoods (-1.0~-1.6 MPa) (Arango-Velez et al. 2011), and cottonwoods have vessel diameters that are similar to H. rhamnoides.

The second Weibull may be due to vessels that are connected exclusively by fiber bridges, as P1/2= -3.5 because fibre bridges are safer.

Additional research is needed to confirm or reject fiber bridge hypothesis.

Cai, Jing, et al. "Recalcitrant vulnerability curves: methods of analysis and the concept of fibre bridges for enhanced cavitation resistance." Plant, cell & environment 37.1 (2014): 35-44.

Thanks for your attention

Email: shan.li@uni-ulm.de