HAL Id: hal-02810888
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Submitted on 6 Jun 2020
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Grassland root system resistance and recovery to a summer extreme.
Marine Zwicke, Julie Laurent, Catherine Picon-Cochard
To cite this version:
Marine Zwicke, Julie Laurent, Catherine Picon-Cochard. Grassland root system resistance and recov- ery to a summer extreme.. Open Science Conference on Climate Extremes and Biogeochemical Cycles in the Terrestrial Biosphere: Impacts and Feedbacks Across Scales, Max-Planck-Institut. Jena, DEU., Mar 2013, Seefeld, Austria. 12 p. �hal-02810888�
Grassland root system resistance and recovery to a summer extreme
Zwicke M, Laurent J, Picon-Cochard C
INRA, Grassland Ecosystem Research, Clermont-Ferrand, Fr
.02
Introduction
Cut-
a
b ab b
a b
b b a
b b b
a
b b b b
b b a
Cut+
Annual production (g m -2 y -1 )
0 200 400 600 800 1000
1200 grasses
legumes forbs
2010 2011
2009
C CX WD WDX C CX WD WDX C CX WD WDX
2010 2009
C CX WD WDX C CX WD WDX
C CX WD WDX
2011
Zwicke et al
•
› vulnerability of mesic grassland production in response to climate change including more severe drought conditions
•
Confirmed in our field site experiment: lagged effects
•
Understand response of grassland root system during and 1 y after
.03
Grassland root system: a tradeoff to find under water deficit
Lichtenegger & Kutschera
SWC -
+ Root
density +
-
?
•
Tolerance of dehydration: increase root lifespan
•
Drought avoidance: › root growth in wet soil layers
•
Root system: key player for drought resistance and recovery
TOLERANCE
AVOIDANCE
TOP
BOTTOM
.04
Aims
• Study root system dynamics in response to reduction of precipitation and warming including a summer extreme
• Is the root system more vulnerable at the top soil layer during the extreme?
• Grassland root strategies of drought resistance?
.05
Altitude: 870 m Annual T: 8°C Annual P: 806 mm
2 cutting frequencies No fertilisation
• Year 1 & 2: Simulation of present and future climate:
co-manipulation of precipitation () and min T ()
(Beier et al 2004)
• Year 1: Simulation of a summer heat-wave (Kimball 2005)
Field site
Resistance recovery
summer Autumn summer
.06
time
WinRhizoTRONMF
~ 3200 images
Minirhizotron
(BTC2, Bartz Technology, CA, USA)
TOP (05cm)
BOTTOM (1520cm)
Root growth
Root lifespan (KaplanMeier)
.07
C CX WD WDX
Cut+
Cut-
Root growth at the end of the extreme
Cut+ Cut-
DOY 202
R oo t g ro w th r at e (m m c m
-2d ay
-1)
0.0 0.4 0.8 1.2 1.6 2.0 2.4
C CX WD WDX 0.4
0.8
1.2 1.6
2.0
TOP
BOTTOM
July
.08
Recovery
C CX WD WDX
Autumn: 3 months after
Cut- Cut+
0.4
0.8
1.2
Cut+ Cut-
DOY 201 R o o t g rw o th r a te ( m m c m
-2d a y
-1)
0.0 0.4 0.8 1.2 1.6 2.0
C CX WD WDX
TOP
BOTTOM
July
1 year after
.09
Root vitality at the end of the extreme:
NIRS spectrum analysis
RMSE
0.0000 0.0001 0.0002 0.0003 0.0004
Cut+
Wavelength (nm)
500 1000 1500 2000
Absorbance(Log1/R)
0.2 0.4 0.6 0.8 1.0 1.2 1.4
C CX W D W DX
Cut-
500 1000 1500 2000 2500
RMSE
0.0000 0.0001 0.0002 0.0003 0.0004
RMSE
0.0000 0.0001 0.0002 0.0003 0.0004
CN-CX WD-WDX
1month death: Picon-Cochard et al, 2009, PSoil
C-CX WD-WDX
1month death: Picon-Cochard et al, 2009, PSoil
Ł Minirhizotron: › Root mortality in C
.010
Median root longevity after 2 years
• › Root longevity under extreme: fl root turnover
• › Root longevity at bottom vs top soil depth
Median root longevity (days)
200 300 400 500 600
C CX WD WDX
Cut+ Cut-
300
400
500
600 TOP
BOTTOM
a a
a
b
a
b b b
b
b b b
a a a a
Cut+ Cut-
TOP
BOTTOM
.011
Conclusions
• At the end of the extreme: low resistance of root growth due to aboveground senescence
Ø
No drought avoidance strategy
• Fast recovery of root growth related to green canopy recovery
• › Root longevity under extreme drought: high tolerance to dehydration
Ø
› carbohydrates: fructans increase stability of membranes
• BUT lagged effect on ANPP observed 1 yr after
Ø
Possible Nlimitation
.012
Climatic treatments
Co-manipulation of precipitation and minimum temperature (passive warming)
based on regionalized (9 x 9 km grid) climate model ‘Arpege4’ (Boé et al., 2006; Déqué, 2007; Déqué et al., 2007)
Present climatic conditions Future climatic
conditions: Night-time warming
Precipitation of 1969- 1999 reference period
Precipitation
reduction in Summer and Autumn of 2040- 2060 period
Automatic rainout shelters (Beier et al, 2004)
Extreme summer event: 2 weeks heat- wave
Day of year
Canopy surface temperature (C)
0 10 20 30 40
50 C, WD
CX WDX
190 193 196 199 202