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Root growth and root respiration of a perennial grassland subject to future climate
Angela Augusti, Mickaël Bahn, D Landais, J Roy, Catherine Cochard
To cite this version:
Angela Augusti, Mickaël Bahn, D Landais, J Roy, Catherine Cochard. Root growth and root respi-
ration of a perennial grassland subject to future climate. 8th Symposium of the International Society
of Root Research, Jun 2012, Dundee, United Kingdom. 2012. �hal-02803326�
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T INRA – Research Centre of Clermont-Ferrand - Theix
Grassland Ecosystem Research 63100• Clermont Ferrand • France www.clermont.inra.fr/urep
Root growth and root respiration of a perennial grassland subjected to future climate change and extreme event
Angela Augusti, Michael Bahn, Damien Landais, Jacques Roy, Catherine Picon-Cochard
picon@clermont.inra.fr
Future climate scenarios suggest not only an increase in atmospheric CO2 concentration and air temperature, but also more frequent and severe extremes events, such as summer heat wave and severe drought. An increase of atmospheric CO2may improve plant growth through its primary effects on both leaf photosynthesis and stomatal conductance. The aim of this work was to test the hypothesis that elevated CO2, combined with air warming and severe soil drought, improves root growth and root respiration through its direct effects on leaf photosynthesis and plant transpiration and indirect effects on soil water content.
Forty-eight grassland monoliths coming from an upland site in France were divided in 12 replicate units and exposed, from May 2010 until December 2011, to a future scenario reproducing air temperature and precipitation (P) expected for the period 2040-2060 (Control: C, +3.5°C, -10% P, annual based). Since March 2011, 6 units were maintained at ambient CO2(380C) and 6 units at +180 ppm [CO2] (520C). In addition, 3 units per [CO2] (380E, 520E) were subjected during summer 2011 to a heat wave (15 days at +6.7°C) combined with a severe P reduction (-100%). Root growth rate was estimated with the in-growth core method (IGC, 15cm depth, 0.754 L). Root respiration (SRR, Licor6400-09 chamber system) and root dry matter content (RDMC) collected in the IGC were measured before, during and after the extreme event.
INTRODUCTION INTRODUCTION
METHODS METHODS
SOIL WATER CONTENT SOIL WATER CONTENT
ROOT RESPIRATION AND MORPHOLOGY ROOT RESPIRATION AND MORPHOLOGY
CONCLUSIONS CONCLUSIONS
• A trade-off was observed between specific root respiration (SRR) and root dry matter content (RDMC)
• RDMC slightly increased in extreme treatments, whereas SRR was unaffected by treatments
Upland grasslands are expected to better recover from a summer extreme event under elevated CO2 combined with warmer and drier climate than actually. Higher canopy photosynthesis and soil water content contributed to higher root growth rate. Thus faster recovery of the below-ground compartment is expected to contribute to grassland survival in future climate.
• Elevated CO2 slightly increased (7%) soil water content (SWC) whatever the period.
• During P reduction but before the heat weave, the effect of elevated CO2 on SWC was more pronounced (+12%)
• During heat weave, rehydration and recovery periods, this effect disappeared
• Drought stress combined with heat weave reduced SWC to values lower than 10%
Acknowledgments
European Project, FP7
ROOT GROWTH RATE ROOT GROWTH RATE
In-growth core
Root respiration
before stress P reduction
Heat weave P addition
Recovery 0
10 20 30
40 380 C
380 E 520 C 520 E depth: 7cm
Specific root respiration (nmol g-1 s-1)
Root dry matter content (g g-1)
0.10 0.15 0.20 0.25
5 10 15 20 25
380C 380E 520C 520E
• Before stress period, there was no differences between treatments
• At the beginning of P reduction, and after heat weave, root growth rate was higher under elevated CO2
• Heat weave sharply decreased root growth, but the recovery was 4 fold higher under elevated CO2
CANOPY PHOTOSYNTHESIS CANOPY PHOTOSYNTHESIS
• Elevated CO2 increased canopy photosynthesis during the experiment in the control treatment
• The CO2effect was maintained during P reduction and sharply increased during the recovery period and was even higher than the control (520E > 520C) at the end of the recovery period
Dates
01/Jun 16/Jun 01/Jul 16/Jul 31/Jul 15/Aug 30/Aug 14/Sep 29/Sep Canopy photosynthesis (g C-CO2 m-2 day-1)
0 1 2 3 4 5 6
380 C 380 E 520 C 520 E
A
B A
AB
B C
A
B
C C
A
A B B
A
B BC C
C: -26 E: -39 C: -61
E: -59 C: -22
E: -54 C: +67
E: -100 C: -35
E: -54
≈0 P reduction vs
actual climate (%)
214 49
42 13
26 Duration (days) 84
All: 3.7 All: 3.8
All: 3.1 C: 3.3
E: 6.7 All: 2.5
All: 3.2 Warmingvsactual
climate (°C)
AVERAGE April-Nov RECOVERY
P ADDITION HEAT
WEAVE P
REDUCTION BEFORE
STRESS TREATMENTS
Root growth rate (g m-2 day-1)
Dates Apr
May Jun Jul
Aug Sep
Oct Nov
Dec 0.0
0.5 1.0 1.5 2.0 2.5 3.0
380 C 380 E 520 C 520 E
*
*
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