Is the biosphere carbon limited?

Is the biosphere
carbon limited?
Christian Körner
Institute of Botany
University of Basel, Switzerland
"Impacts of climate change", EXPO 2015 Milano, 23 June 2015
In Geneva 210 years ago:
‘The primary plant food
comes from air‘
- Nicolas-Théodore de Saussure (1804)
Recherches chimiques sur la Végétation. Paris.
Paving the road:
- Jan Ingenhousz (1779)
Experiments upon vegetables, discovering their
great power of purifying thecommon air in the
sun-shine, and of injuring it in the shade and at
night. P. Elmsly and H. Payne, London, UK.
- Jean Senebier (1783)
Recherches sur l’nfluence de la lumière solaire
pour métamorphoser l’air fixe en airpur par la
vegetation. Barthelemi Chirol, Geneva,
Switzerland.
1.5 mm C
1-2 Gt C
7-8 Gt C
© Ch Körner
Atmosphere
+1 to +2 a -1
Plant mass
Soil humus
Shallow soil
(0-1 m)
Deep soil
(1-2 m)
62-63 a -1
61 a-1
650
1500
795
+ 4.5 a -1
1-2 a-1
ca. 8 a -1
Pg C for pools and
Pg C/yr for net fluxes
46
44
+3.5 a -1
Ocean
~700
surface water
Shallow ocean
~500 organic sediments
< 0.2 Gt a -1
900
deep ocean water
and rocks > 6 x 107
> 6500 fossil organic C
© Ch Körner
Sequestration = Storage
650 Gt C
2400 Gt C
© Ch Körner
Atmospheric CO2 at Mauna Loa Observatory
June 2015
CO2-concentration (ppm)
400
400 ppm
2015
Ice core data
360
320
Cold
Warm
280
1750
240
200
180 ppm
160
800'000 700'000 600'000 500'000 400'000 300'000 200'000 100'000
Years before today
Lüthi D et al (2008) Nature 453:379
0
© Ch Körner
180
280
380
580 ppm CO2
Atmospheric CO2
Climate effects
Direct biological effects
Indirect effects
© Ch Körner
50 % of plants = C
© Ch Körner
0
50
100
150
200
250 Mrd t C
Tropical rainforest
41.6 %
Subtropical forest
14.1 %
Boreal forest
13.0 %
Temperate deciduous forest 11.4 %
Temperate evergreen forest
9.5 %
Savanna
3.2 %
Shrubland
2.7 %
Wetlands
1.6 %
Temperate grassland
0.8 %
Farmland
0.8 %
Semideserts
0.7 %
Tundra
0.3 %
Forest
Non-forest
For C-storage
in biomass only
trees matter
(>86 %)
100 % = 652 Mrd t C
© Ch Körner
Hierarchy of controls
Carbon uptake and carbon use by plants
C-source:
CO2-Assimilation
Limitation
by resources
other than C
(nutrients, water,
temperature)
Limitation
by light,
[CO2]
C-sink:
Growth (NPP)
Respiration
Growth
Export
© Ch Körner
C source activity rarely controls sink activity
Source
(photosynthesis)
Transport of
building material
Sink
(growth)
Körner C (2012) Biologie in unserer Zeit 4:238
Körner C (2013) Nova Acta Leopoldina NF 114, 391:273
© Ch Körner
Source
Sink balance
Drought
Low temperature
Nutrient limitation
Körner C (2015) Curr Opin Plant Biol 25:107
Fatichi S et al (2014) New Phytol 201:1086 © Ch Körner
The ecosystem carbon cycle is driven by the
nutrient cycle and other growth ‘facilitators‘
CO2
Carbon
cycle
coupling
Mineral
nutrients
Mineral
nutrient
cycle
© Ch Körner
Horticular systems are decoupled
from the natural nutrient cycle
© Ch Körner
Growth rate should never be confused with C-storage
© Ch Körner
... the more older trees the more carbon
The C-capital (storage) is controlled by tree
demography (residence time of C)
Growth, NPP
CO2
Fluxes do not
scale to pools
!
NEP
Change of
pool size
f (input-output)
Harvest
Mortality
Recycling
Finite storage capacity
f (soil, climate, taxa, vigor)
Körner C (2006) New Phytol 172:393
Bugmann H, Bigler C (2011) Oecologia 165:533
CO2
© Ch Körner
Rates (productivity, growth) versus [cash flow]
Pools (biomass, C-storage)
[capital]
Biomass C-pool (%)
Slow turnover
Fast turnover
100
Mean
50
C-pool
0
0
100 0
100 0
Time (years)
A growth stimulation (experiments) should never be
confused with landscape-wide carbon sequestration
C-sequestration in biomass is a demography issue.
Körner C (2006) New Phytol 172:393
100
© Ch Körner
• All trees grow until trees die.
We do not need science to prove this.
That is why we have foresters!
• A growing tree does not sequester C
unless the mortality or harvest of another
tree is prevented.
© Ch Körner
Is carbon a limiting resource?
© Ch Körner
CO2
web-FACE at the Swiss Canopy Crane site
Gas
analysis
Gas control
CO2 + 13C tracer
© Ch Körner
Tree ring width
(standardised by 1990-1999 pre-treatment mean)
1.5
No change in growth of 100 year old decidous trees
in elevated CO2,
Fagus
Swiss web-FACE
1.0
Ambient CO2
Elevated CO2
0.5
0.0
1.5
Quercus
1.0
0.5
0.0
1.5
Tilia
Bader MKF et al (2013)
J Ecol 101:1509
1.0
and similar results by
0.5
0.0
Sigurdsson BD et al (2013)
Tree Physiol 33:1192
2001 2002 2003 2004 2005 2006 2007 2008
Year
© Ch Körner
20 m
10 m
0
High
1.5
Ambient CO2
Elevated CO2
FACE
1.0
0.5
0.0
1.5
Mid
30 m
2.0
1.0
0.5
0.0
1.5
Low
40 m
Annual tree BAI
(standardized by 2005-2009 pre-treatment mean)
No growth effect of elevated CO2 on Picea abies
1.0
0.5
0.0
T Klein & C Körner, unpubl
2002 2004 2006 2008 2010 2012 2014
Year
© Ch Körner
Conclusions for
CO2 effects on plants
• Carbon sinks control C sources
(mostly).
• Forest productivity is not
C limited.
• C sequestration in forests
requires a longer residence
time of C (tree demography
matters).
© Ch Körner
Priority in theory and modeling of plant growth or NPP
Old model
(sources control sinks)
New model
(sinks control sources)
C-uptake
Other drivers
Other drivers
C-uptake
CO2 acquisition has
priority over any
other growth control
Meristem activity
determines C-demand,
and thus, C uptake
Körner C (2015) Curr Opin Plant Biol 25:107
Fatichi S et al (2014) New Phytol 201:1086
© Ch Körner
The enhanced greenhouse effect can be
mitigated
1) by reduced carbon release
2) by carbon capture and storage
technologically
biologically
3) by substitution of fossil carbon by renewable
energy sources
technologically
biologically
© Ch Körner
Pretentious claims for mitigation by C storage
• Afforestation takes 100-200 years to pay the
debth of cutting
don‘t cut in the first place
• Enhanced storage by stocking (more C by unit
land area)
limited, can be done only once, risk of windthrow
• Expand forest area at the cost of other land area
competion with agriculture
© Ch Körner
‘Replacing fossil by renewable C?
‘Fuel crops‘?
The total fossil C-savings are close to zero, when
the total environmental footprint is accounted for.
1l fossil oil for
1l rape oil
Zah R et al (2007) EMPA, BFE Bern
© Ch Körner
Substitution potential in % of fossil C emission (100%)
4.7%
5.1%
Annual timber yield
Carbon (Mio t C)
10
10 t C ha-1 a-1 biomass production
on 10 % of arable land
5
8.2%
2.3%
0
Germany
Switzerland
3-5 % of bio-fuel-carbon (substitution) corresponds to driving
with 6.1 (D) or 6.3 (CH) instead of 6.6 litres gasoline per 100 km.
Körner C (2004) Nova Acta Leopoldina NF 91, 339:287-303
© Ch Körner
Energy crops should be forbidden!
• They allocate food production elsewhere
• They rise food prices
• They are commonly not produced sustainably
• They lead to N2O emission and groundwater
pollution if productive
• They commonly require pesticide application
ChKörner
Körner
©Ch
Pretentious claims in the context of green
options to mitigate the climate change
The net saving of the fossil energy is very small:
• Afforestation: better don't clearcut in the first place
• Fuel crops: not efficient, compete with food
• Bioenergy: effects are tiny (mainly waste combustion)
© Ch Körner
... fully accounting for all costs and benefits there is little
potential for substituting fossil energy with bioenergy
by more than 3-5 % of current total consumption.
The future is solar ...
© Ch Körner
• The current biosphere is
carbon saturated.
• There is no 'benefit'
of a CO2-rich atmosphere.
• There is no 'green solution'
to the CO2-problem.
© Ch Körner