Institute of Horticultural Production
Systems
Vegetable Systems Modelling
Plant canopies under drought stress– structures,
functions, (genes) and models
Hartmut Stützel and Tsu-Wei Chen
Plant canopies: structural and functional properties
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Leaf area index
Inclination of leaves
Leaf angle distribution
Leaf curvature
Optical properties
Light extinction coefficient
Gap fraction
Internode length
 Canopy photosynthesis
 CO2 transport (stomatal,
mesophyll resistance)
 Biochemical conversion
(Rubisco, light)
 Transpiration
Light intensity, light quality and availability of water
Canopies under stress
2
How are these functional and structural properties
influenced by stress?
How can we quantify stress effects on function and structure?
Canopies under stress
3
35
6
25
20
15
10
Flag leaf length (cm)
5
Leaf angle (°)
Specific leaf weight (mg cm-2)
Flag leaf length, leaf angle
30
5
4
3
Flag leaf
2
Third leaf
1
0
0
0
100
200
300
Irrigation (mm)
0
100
200
300
Irrigation (mm)
Morphological traits of wheat as related to water supply
Canopies under stress
after data fom Zhang et al. 2011
4
Simulated diurnal time
course of net canopy
photosynthesis for a
maize crop having leaf
area index (L) of 2, 4,
or 8 and average leaf
inclination from the
horizontal of (a) 40°or
(b) 80°. Simulation
conducted for Day 180
of the year at Johnston,
IA (41°40′ N lat)
Canopies under stress
Hammer et al. 2009
5
130%
70%
Canopy light interception: 78%
Light extinction coefficient: 0.60±0.02
Canopy light interception: 49%
Light extinction coefficient 0.27±0.01
Simulated effects of increasing and decreasing leaf angle
by 30 % on light extinction coefficient and Light
interception of tomato canopies
Canopies under stress
Chen et al. 2014, J. exp. Bot., accepted
6
Response of net photosynthetic CO2 assimilation (PN) to intercellular CO2
concentration (ci) of barley plants grown at ambient (A) and elevated (B) [CO2]
and subjected to well-watered conditions (circles) or 9 (squares), 13 (triangles)
and 16 d (diamonds) of water stress.
Canopies under stress
Robredo et al. 2010
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Generalized response of net photosynthesis (AN) and several parameters
related to photosynthetic capacity to water stress when using daily maximum
leaf stomatal conductance (gs) content as the reference for stress intensity
Canopies under stress
Flexas et al. 2012
8
Modelling canopy processes
 Big leaf models: treat the canopy as an extended leaf (or a
small set of large leaves), map the properties of a whole
canopy onto a single leaf (or a few leaves, Amthor, 1994)
 Sunlit-shade models: divide the (big leaf) canopy and leaf
nitrogen between sunlit and shaded leaves (de Pury and
Farquhar 1997)
 Multi-layer models: canopy is divided into layers, each with
different light level, predicted by Beer’s law, and differentiation
into sunlit and shade leaves (including a sunfleck penetration),
a coupled scheme of leaf photosynthesis and stomatal
conductance (Clark et al., 2011)
→ no precise prediction of the spatial and temporal heterogeneities of light inside a canopy
Canopies under stress
9
Diurnal canopy CO2 uptake rate (Ac) of a rice canopy calculated with average
photosynthetic photon flux density (PPFD) at different layers of a canopy
(average light) compared with Ac calculated using the detailed PPFD of each
individual facet in the canopy (detailed light).
Canopies under stress
Song et al. 2013
10
Spatially explicit models of canopies: Functionalstructural plant models (FSPM)
Structure
Environment
Functions
Canopies under stress
 Simulate plant growth and
development based on
individual organs
 Explicitly allow for
feedbacks between plant
structure and plant
function
 Interactions between
organs
 Canopies are constructed
as assemblies of plants
 Static
 Dynamic
11
Dynamic cucumber
architecture model
Structure
Environment
Functions
Canopies under stress
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The virtual 2 m cucumber canopy with 18 plants, constructed using digitized data in
GroIMP, in top view (A) and side view (B).
Canopies under stress
Chen et al. 2014; doi:10.1093/aob/mcu100 13
An example of dynamic functional-structural plant model
(L-Peach, Allen, Prusinkiewicz and DeJong, 2005)
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Functional-structural models: research questions
 Spatial integration of processes
 Effects of physiological limitations on canopy performance
 Effects of light direction (e.g. direct/diffuse) on growth
 Disentangling physiological from morphological effects
 Influence of canopy architecture modifications: row width,
plant density etc.
 Assessment of plant traits: breeding, pruning ….
Canopies under stress
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Simulated leaf photosynthesis rate under 100 % direct light and 100 % diffuse
light in a cucumber canopy
Canopies under stress
Chen et al. 2014; doi:10.1093/aob/mcu100 16
Analysis of limitations to productivity:
 Physiological limitations
 Photosynthesis
 CO2 diffusion
 Biochemical apparatus
 Light
 Structural limitations
 Leaf area
 Leaf area distribution
 Leaf exposition: leaf angle, azimuth angle
Canopies under stress
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Photosynthesis (mol CO2 m-2 s-1)
35
Reference photosynthesis rate
30
Biochemical limitation
25
Current
photosynthesis
rate
20
15
Light limitation
Diffusional limitation
10
J = Jref
5
J = Jmax
Current
CO2 conc.
0
50
100
150
J
200
250
300
350
-1
Chloroplastic CO2 concentration (mol mol )
Calculation of photosynthetic limitations due to
biochemical, light and diffusional factors
Canopies under stress
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Changes of
(A) stomatal,
(B) mesophyll,
(C) diffusional
(stomatal +
mesophyll),
(D) biochemical,
(E) light and
(F) total (diffusional +
biochemical +
light) limitations
with leaf rank
(counted from
bottom to top)
and light
conditions above
the canopy (79 %
direct light and 21
% diffuse light)
Canopies under stress
Chen et al. 2014; doi:10.1093/aob/mcu100 19
Canopies under stress
Chen et al. 2014; doi:10.1093/aob/mcu100 20
Simulated relationships between water potential in the root zone
and photosynthetic limitations of a cucumber leaf on day 15 after
leaf appearance. The environmental conditions were: ambient
CO2 concentration = 380 ppm, water vapour deficit = 0.87 kPa,
leaf absorbed light intensity = 800 µmol m-2s-1, and leaf
temperature = 25°C.
Canopies under stress
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18
Photosynthesis rate
( mol CO2 plant-1 s-1)
16
Non-stress
14
12
10
8
6
4
2
0
0
200
400
600
Light interception ( mol photon plant-1 s-1)
18
Photosynthesis rate
(mol CO2 plant-1 s-1)
16
Drought stress
14
12
10
8
Simulated
effects of
drought stress
(soil water
potential - 0.4
MPa) on photosynthesis rates
at different
positions in a
cucumber
canopy
6
4
2
0
0
200
400
600
Light interception (mol photon plant-1 s-1)
Canopies under stress
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Light use efficiency
( mol CO2 mol-1 photon)
0.05
Non-stress
0.04
0.03
0.02
0.01
0.00
0
200
400
600
Light interception ( mol photon plant-1 s-1)
Light use efficiency
( mol CO2 mol-1 photon)
0.05
Drought stress
0.04
Simulated effects of
drought stress (soil
water potential - 0.4
MPa) on light use
efficiencies at
different positions
in a cucumber
canopy
0.03
0.02
0.01
0.00
0
200
400
600
Light interception ( mol photon plant-1 s-1)
Canopies under stress
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Influence of drought stress (water potential Ψs = -0.4
MPa in the root zone) on canopy photosynthesis and
light use efficiency in different positions of the canopy
upper
Maximum Ac (µmol
plant-1 s-1)
Maximum LUEc (µmol
CO2/µmol PAR)
Ic for maximum LUEc
(µmol plant-1 s-1)
Non-stress
Drought
Non-stress
Drought
Non-stress
Drought
5.9
5.1
0.046
0.041
49.0
44.9
Canopies under stress
middleupper
4.3
3.7
0.040
0.035
55.7
50.9
Canopy part
middlelower
3.9
3.4
0.033
0.029
59.3
60.6
lower
1.6
1.5
0.026
0.023
38.6
37.8
whole
plant
15.6
13.7
0.038
0.033
231.0
214.6
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What happens under salinity?
Osmotic
stress
Ionic stress
(ion accumulation)
red.
Toxic
red.
red.
Biochemical
capacity
Non-architectural
effects
Organ size
Photosynthesis
Architectural
effects
Light use
efficiency
Transpiration
Ion accumulation
Stom. conduct.
Light interception
Canopies under stress
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Shoot dry mass (% of control)
110
100
y = 100 -0.34x
R2 = 0.91
90
80
y = 100 -0.49x
R2 = 0.99
70
Low temperature
High temperature
60
0
20
40
60
80
Salinity level (mM NaCl in nutrient solution)
Effect of salinity on shoot dry mass on day 77 after the first leaf
appearance under 22/18°C (low temperature) and 32/28°C (high
temperature) day/night temperature conditions
Canopies under stress
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Relative light use efficiency at three salinity levels under low (LT,
22/18°C) and high (HT, 32/28°C) day/night temperature
conditions
Day
29-35
36-43
44-50
51-56
57-63
64-70
71-77
40 mM
LT
HT
1.17 1.07
1.10 1.06
1.05 1.02
1.07 1.02
0.97 0.93
1.05 1.05
0.93 0.96
Canopies under stress
60 mM
LT
HT
0.96 0.93
0.88 0.91
0.85 0.86
0.86 0.85
0.78 0.79
0.73 0.89
0.75 0.83
80 mM
LT
HT
0.80 0.81
0.69 0.78
0.68 0.73
0.66 0.72
0.64 0.67
0.66 0.75
0.61 0.71
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110
Architectural effects on shoot
dry mass (% of control)
Shoot dry mass (% of control)
110
100
90
80
70
Low temperature
High temperature
60
0
20
40
60
80
Salinity level (mM NaCl in nutrient solution)
100
90
80
70
60
30
40
50
60
70
80
90
Salinity level (mM NaCl in nutrient solution)
Total and architectural effects of salinity on shoot dry mass on day 77 after
the first leaf appearance under 22/18°C (low temperature) and 32/28°C
(high temperature) day/night temperature conditions
Canopies under stress
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Conclusions
 A canopy is more than a big leaf
 Canopy structure has strong impact on productivity and
resource use → optimization
 Systematic analysis of architectural effects on productivity and
resource use is just at the beginning
 FSPM are models
Canopies under stress
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Thank you!
Canopies under stress
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