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Belowground carbon demand causes early culmination of radial stem growth in Norway spruce exposed to drought stress in spring
Walter OberhuberAndreas Gruber
Gina Rainer-LethausAndrea WinklerGerhard Wieser
General Assembly9-13 Apr 2018 Vienna, Austria
Austrian Science Fund
Dry inner alpine valley
Background
Oetz (775 m)7.3 °C 714 mm
J F M A M J J A S O N D
Prec
ipita
tion
(mm
)
Tem
pera
ture
(°C
)
20
10
0
20
0
40
80
60
100
Pinus sylvestris, Picea abies, Larix decidua
5 - 10 cm15 - 20 cm
750 m a.s.l.
Background
Climate-growth relationships
Schuster and Oberhuber (2013) Trees
A M JC
oeffi
cien
t
Precipitation in spring favours radial stem growth
Early culmination of radial stem growth
Pinus sylvestrisLarix decidua
Picea abies
7.3 oC 714 mm
J F M A M J J A S O N D
Prec
ipita
tion
(mm
)
Tem
pera
ture
(oC
)
20
10
0
20
0
40
80
60
100
Oberhuber et al. (2014) Eur J For Res
Maximum radial stem growth
Intra-annual dynamics of radial stem growth
Carbon allocation belowground is prioritized over radial stem growthunder drought
90 Norway spruce treesc. 1.5 m height and 6 yr old
watered drought-stressed 18.1 ± 3.9 %
9.0 ± 1.9 %
Hypothesis
Upper zone (UZ)
Middle zone (MZ)
Lower zone (LZ)
Cambium marking
NSC-content: determined after the growing seasonin UZ, MZ and LZ and coarse roots
Double girdling
cambial zonephloem
bark
P
woundingin mid-May
2014
2015
growth ring boundary
growth after wounding
growth beforewounding
Experimental design
Growth-regulating factors (auxin, cytokinin) ?
watered trees
drought-stressed trees
growth onset
end
end
Girdling at different phenological stages
double girdlingdates
GD 177 doy
GD 2138 doy
GD 3190 doy
Oberhuber et al. (2017) Env Exp Bot
Upper zone
2014
2015girdling and ‚pinning‘ in May
cambial zonephloem
growth after girdling
growthbeforegirdling
Girdling during the growing season - watered tree
growth ring boundary
Middle and lower zone
2014
2015
cambial zonephloembark
growthbeforegirdling
NO growthafter girdling
Upper zone
Middle zone
Lower zone
Winkler and Oberhuber (2017) Tree Physiol
controlgirdling in July
Girdling after the end of the growing season - drought stressed tree
latewood
earlywood
cambialreactivationafter girdling
traumaticresin ducts
cambial zonephloem
bark
cambial zonephloem
bark
drought
Radial stem growth in response to girdling
drought stressed
watered
girdling datesMarch May July
minirhizotron technique
Fine root mass in response to girdling
Rainer-Lethaus and Oberhuber (2018) Front Plant Sci
control
GD doy 77
GD doy 138
GD doy 190
Longitudinal root growth after girdling - drought stressed treeGrowth onset
Rainer-Lethaus and Oberhuber (2018) Front Plant Sci
Rainer-Lethaus and Oberhuber (2018) Front Plant Sci
Radial root growth in response to girdling
drought stressed
watered
Carbon status in girdled trees - stem
Oberhuber et al. (2017) Env Exp Bot
drought stressedwatered
control
Carbon status in girdled trees – coarse root
Oberhuber et al. (2017) Env Exp Bot
drought stressedwatered
control
Decrease in starch content:radial growthmaintenance respirationresin production
Summary
• radial growth increase was more intense under drought
• reactivation of cambium activity in drought-stressed trees
In response to phloem girdling:
• altered C availability stimulated radial growth
• decrease in starch content (except shoot)
Conclusion7.3 oC 714 mm
J F M A M J J A S O N D
Prec
ipita
tion
(mm
)
Tem
pera
ture
(oC
)
20
10
0
20
0
40
80
60
100
Thank you for your attention Austrian Science Fund
Belowground carbon demand causes early culmination of radial stem growth under drought
Shoot growth
Oberhuber et al. (2017) Env Exp Bot