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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

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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

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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