HAL Id: hal-02089535
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Submitted on 5 Jun 2020
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Dynamics of xylem cavitation during a simulated
drought in Eucalyptus camaldulensis saplings, a species
with solitary vessels
Tete Severien Barigah, J. Gyenge, F. Barreto, Philippe Rozenberg, M.E.
Fernandez
To cite this version:
Tete Severien Barigah, J. Gyenge, F. Barreto, Philippe Rozenberg, M.E. Fernandez. Dynamics of
xylem cavitation during a simulated drought in Eucalyptus camaldulensis saplings, a species with
solitary vessels. International Conference “Adapting forests ecosystems and wood products to
bi-otic and abibi-otic stress”, European Union Marie-Curie project TOPWOOD., Mar 2019, Bariloche,
Argentina. 1 p. �hal-02089535�
Aims
Dynamics of xylem cavitation during a simulated drought in
Eucalyptus camaldulensis saplings, a species with solitary vessels
Barigah TS
1
, Gyenge J
2-3
, Barreto
2-3
F, Rozenberg P
4
& Fernández ME
2-3
tete-severien.barigah@inra.fr
1
INRA,UMR0547 Physique et physiologie Intégratives de l'Arbre en environnement Fluctuant (PIAF) Clermont-Ferrand, France
2CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
3
INTA, Instituto Nacional de Tecnología Agropecuaria, Ecología Forestal, AER Tandil - EEA Balcarce, Argentina
4INRA, UR0588 Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt (BioForA) Orléans, France
Material and methods
Results
The aims of this study were to unravel the dynamics of embolism spread in the complex xylem vessel-structure for potted saplings of E. camaldulensis assigned to simulated
protracted water stress.
We carried out a pot experiment on 48 saplings of E. camaldulensis under a 12 m² shelter in the city of Tandil (37° 19’S; 59° 09’W, 188 m a.s.l.), Argentina.
We relied on staining and hydraulic methods to test for links between xylem anatomical features and the propagation of embolism within the study plants. We used safranin solution
to assess sapwood area traits of 8 control and 9 water-stressed saplings. We chose them as to cover roughly a range from 15% to 100% percent loss hydraulic conductance (PLC). We
completed additional measurements such as predawn and leaf water potential (
Y), stomatal conductance (g
s) and soil water content (SWC).
• We found that the mean native embolism rates were similar for all the plants during the 15 days after the onset of the water stress treatment. PLC was very variable, from 15% up to 71% in
some individuals, irrespective of the treatment. This could be a matter of the high proportion of the embolized vessels: high in the inner but variable in the outer section of the sapwood
area.
• We came to a good correlation between PLC (hydraulic method), the proportion of stained sapwood area and the percent of unstained vessels (staining methods). Based on the mean size
of the vessels, embolism occurred randomly in the sapwood. Indeed, the sensitivity of the study Eucalypt species was not a matter of vessel diameter.
• When considering the vessel diameter distribution, we also observed a significant increase in the probability of embolism occurrence in the smallest vessel range for plants with a
relatively low proportion of unstained vessels only.
• Besides, it rose from our study that saplings of E. camaldulensis could recover from a severe water-stress unless their percent loss hydraulic conductance was lower than 77%. Anyhow,
no post-drought recovery occurred when the PLC is equal or greater than 85%.
With the ongoing climate change, water stress is prone to become a commonplace event leading plant growth and productivity worldwilde under threat because of the disruption of
their water status. Forests are highly sensitive to climate change due to the lack of sufficient knowledge related to tree adaptive responses to environmental fluctuations. Structural
and physiological adaptations to drought require complex interactions between anatomy, physiology and biochemistry. Thus, long term maintenance of hydraulic integrity is crucial
for survival of tree, including important forestry species that are widely distributed worldwide such as Eucalyptus camaldulensis. Xylem, the main pathway for water transport over
long distances of this species, is made of solitary vessels surrounded by different imperforate tracheary elements and parenchyma that may influence in a poorly known way their
xylem safety and hydraulic efficiency.
Introduction
Potted Eucalypt saplings
Soil water content, %
10 20 30 40 P re d a w n w a te r p o te n ti a l, M P a -7 -6 -5 -4 -3 -2 -1 0 y = - 0.0069 * x2 + 0.502 * x - 9.3975 r2 = 0.838; P < 0.0001
Conclusions
Predawn water potential over time for control and treated plants.
Ypddropped within the 15 days since the water withholding of
the treated plants
Pattern of percent loss hydraulic conductance for control and treated saplings versus time.
Even high, the rate of native embolism (PLC) was similar for both the control and treated plants during the fortnight after the onset of the experiment. But thereafter, PLC for treated plants rose sharply to more than 90% while PLC levelled off for control plants.
Percent loss hydraulic conductance (hydraulic method) was highly correlated with percent stained sapwood area (staining method).
y = -0.8305x + 92.7196; r² = 0.80
Left panel - Mean± SE diameter of stained and unstained vessels in different
sections of the xylem (inner and outer sapwood) in differently embolized plants. There was no significant difference in the mean size of stained and unstained vessels (Tukey test, p<0.05).
Right panel - Percent of unstained vessels in inner and outer portion of sapwood in plants with different degree of PLC. Proportion of unstained vessels was high in all plants (even control plants). It increased steadily in the inner area along the drying steps while this proportion remained low in the outer part when PLC was lower than 70% but increased sharply for highly stressed plants.
Dates 30/01/17 13/02/17 27/02/17 13/03/17 27/03/17 10/04/17 P e rc e n t lo s s h y d ra u li c c o n d u c ta n c e , % 0 20 40 60 80 100 Control plants Treated plants Dates 30/01/17 13/02/17 27/02/17 13/03/17 27/03/17 10/04/17 P re d a w n w a te r p o te n ti a l, M P a -8 -6 -4 -2 0 Control plants
Tre ate d plants Es tim ate d from SWC
Relationship between leaf predawn water potential and the soil water content.
Progressive decrease inYpdwith drying soil.
Upper panel - Size distribution of unstained vessels in plants with low proportion of embolized vessels was significantly different from that expected by chance and, the highest deviation was in the
lowest vessel size range (Chi2test, p<0.05).
Lower panel - Size distribution of unstained vessels in plants with high proportion of embolized vessels followed the expected vessel
size distribution of the entire sapwood area (Chi2test, p>0.05).
Pressure chamber Hydraulic conductance
measurement
Computing sapwood anatomy features Cut section of distal
shoots immersed in safranin solution Cutting shoot under
safranin solution
Assessing inner and outer stained and unstained vessels in
sapwood section area
Vessel size classes
0-10 10-15 15-20 20-25 25-30 >30
F
re
q
u
e
n
c
y
,
%
5
10
15
20
25
30
B
F
re
q
u
e
n
c
y
,
%
5
10
15
20
25
30
35
Unstained Stained and UnstainedA
Percent unstained vessels: 18.1 ± 10.6%Percent unstained vessels: 70.5 ± 32.7%
*
This study was funded by the EU H2020-MSCA-RISE-2014 project TOPWOOD (Wood phenotyping tools: properties, functions and quality – 645654). The authors are grateful to the field assistants for their help and for the grant .
Acknowledgements
Inner Outer Whole area
20 40 60 80 100 Samples with PLC > 70% P e rc e n t n o n -c o n d u c ti v e v e s s e ls a n d p e rc e n t lo s s h y d ra u li c c o n d u c ta n c e , % 20 40 60 80 100 Samples with 40 < PLC < 70% 20 40 60 80 100
Percent unstained vessels Percent loss hydraulic conductance
Samples with PLC < 40%
Location within the cross-sectional area
Inner Outer Whole area
V e s s e l d ia m e te r, µ m 10 15 20 25 Samples with PLC > 70% V e s s e l d ia m e te r, µ m 15 20 25 Samples with 40 < PLC < 70% V e s s e l d ia m e te r, µ m 15 20 25 Stained vessels Unstained vessels Samples with PLC < 40% A B C D E F
