1.
H d li ti ti t bli h t d ff t fHydraulic activation: establishment and effects of
liquid water bridges across the stomata
Jürgen Burkhardt Shyam Pariyar Mauricio HunscheJürgen Burkhardt, Shyam Pariyar, Mauricio Hunsche
Institute of Crop Science and Resource Conservation
University of Bonn, Germany
ESA 100, Baltimore, USA, 12th August, 2015

2.
Research questions
What is the influence of leaf surface particles
(deposited aerosols) on the(deposited aerosols) on the
- duration of foliar micro-wetness ?
- water surface tension on leaves ?
- stomatal liquid water transport ?stomatal liquid water transport ?

3.
Dew chemistry from Scots pine and neighboring Norway spruce
uce
atio
ayspru
ationra
e/Norw
ncentra
otspine
Con
Sco
 Dew chemistry is governed by deposited aerosols
(Burkhardt 1989)

4.
Electrical conductance on spruce needles
14 m height
emens] relative humidity
100
80
1,4
g
dle[10-9
sie
%]
e a e u d y
8060
1 0
1,2
pruceneed
humidity[%
60
40
0,8
1,0
ation[mm]
uctancesp
relative
spruce needle
conductance
40
0,4
0,6
precipita
tricalcondu
spruce needle
0
2020
0,2
,
rainfall
i it ti
elect
CET
0
12 18 0 6 12 18 0 6 12 18 0 6
0
0,0
precipitation
10.8.92 11.8. 12.8. 13.8.
CET
(Burkhardt & Eiden, Atm. Env. 1994)

5.
22
s]
80
100
dle[10-9
siemens
%]
relative humidity
20
40
60
ncespruceneed
lativehumidity[%
conductance
18
0
20
ectricalconducta
re
spruce needle
conductance
emens]
relative humidity
100
80
1,4 11.8.92 12.8.92
CET
12 18 0 6 12 18
0
ele
pruceneedle[10-9
sie
humidity[%]
60
80
40
60
0,8
1,0
1,2
ation[mm]
tricalconductancesp
relative
spruce needle
conductance
0
20
40
20
0,2
0,4
0,6
precipita
rainfall
i it ti
elect
10.8.92 11.8. 12.8. 13.8.
CET
0
12 18 0 6 12 18 0 6 12 18 0 6
0
0,0
precipitation
(Burkhardt & Eiden, Atm. Env. 1994)

6.
90
28
ns]
80
90
28
mens] 80
26 relative humidity
sieme
70
80
26 relative humidity10-9
siem
60
70
24
ce[10-9
y[%]
60
24
tance[1
midity[%]
50
60
22
uctanc
ehumidity
el conductance on spruce needle 40
50
20
22
conduct
relativehum
el. conductance on spruce needle
40
20
lcond
relative
el. conductance on spruce needle
30
40
18
ectricalc
r
3018
ectrica
0 3 6 9 12 15 18 21
2016
ti [h]
ele
0 3 6 9 12 15 18 21
2016
ele
time [h]
NH3 added
 ‘ ‘time [h]
(Burkhardt & Eiden, Atm. Env. 1994)
Ammonia dissolves  ‘real water‘

7.
Comparison of leaf
wetness sensorswetness sensors
Potato field, southern Germany,hot summer week
Burkhardt &
HunscheHunsche,
Frontiers in
Plant Science,
2013

8.
Foliar micro-wetness
Water vapor from atmospheric humidity and/or fromWater vapor from atmospheric humidity and/or from
transpiration, condensing to hygroscopic leaf
surface particlessurface particles.
Particles act similar to cloud condensation nucleiParticles act similar to cloud condensation nuclei.

9.
turbulent boundary
layeraye
laminar boundary layery y
Spruce needle
Substomatal
cavity

10.
Deliquescence:Deliquescence:
the process by which a
substance absorbs moisture
from the atmosphere until it
dissolves in the absorbed
water and forms a solutionwater and forms a solution
Deliquescence humidityDeliquescence humidity
DRH (NaCl): 75%
DRH (NaClO3): 75%
DRH (CaCl2): 32%
DRH (NH4HSO4): 40%
DRH ((NH ) SO ): 80%
DRH
DRH ((NH4)2SO4): 80%

11.
66% RH
50 100 %RH75

12.
Stomatal water uptake?
‚NO‘ - Based on
- droplets/stomatal geometry
- cuticular hydrophobicity
water surface tension- water surface tension
- pure water, clean surface
(Schönherr & Bukovac,
Plant Phys., 1972)
• Stomatal geometry not relevant for thin films
• Hygroscopic particles reduce hydrophobicity
• Reduced water surface tension of concentrated solutions (ion
specific)

13.
Franz Hofmeister,
physiologistphysiologist
1850 - 1922
Arch Exp Pathol Pharmakol. (1888):

14.
(‘lyotropic series‘)
IO3
- F-
chaotropic
‘structure-breakers‘
kosmotropic
‘structure-makers‘
protein solubilityprotein solubility
hydrophobicity
surface tensionsurface tension

15.
Environmental Pollution, 2014, supplementary file

16.
Section of stoma of an onion leaf with salt particle (P) on surface
GC: guard cell, SW: stomatal wall, SSC: substomatal cavity
Burkhardt, Ecol. Monographs, 2010

17.
CeCl3 auf Zwiebelblatt
Hydraulic activation of stomata (HAS) – bidirectional exchange of water, solutes,
information (hydraulic signalling). Burkhardt, Ecol. Monographs, 2010

18.
eCl3 auf Zwiebelblatt
HAS enables second pathway of stomatal transpiration
Burkhardt, Ecol. Monographs, 2010

19.
Epidermal minimum conductance (gmin) of Scots pine
needles increases by spraying with salt solutions
1.5
needles increases by spraying with salt solutions
1 0
***
m‐2s‐1)
1.0
** ***
*
***
(mmolm
0.5
gmin
0.0
H2O (NH4)2SO4 NaCl NaCl+
surfactant
NaNO3 KI (Burkhardt & Pariyar,
Env Poll 2014)surfactant
High gmin  low drought tolerance
Env. Poll., 2014)

20.
Summary and conclusions
F li i t i f d b l f f ti l iFoliar micro-wetness is formed by leaf surface particles, air
humidity, and transpiration. May be permanently present.
Fluctuations of relative humidity can cause dynamic particle
expansion into the stomata (HAS)expansion into the stomata (HAS).
HAS affects individual stomata; depends on the amount, thep
deliquescence point and the chaotropicity of particles/ions.
HAS potentially enables stomatal water uptake in fog forests.
Deposited aerosols may be part of stomatal functioningDeposited aerosols may be part of stomatal functioning.
Aerosol pollution potentially decreases drought tolerance.p p y g

21.
Acknowledgements
Knut Wichterich
Effects of Climate Change on Air Pollution andg
Response Strategies for European Ecosystems