plant canopies under drought stress– structures, functions, (genes) and models

Institute of Horticultural Production SystemsVegetable Systems Modelling

Hartmut Stützel and Tsu-Wei Chen

Plant canopies under drought stress– structures, functions, (genes) and models

2

Plant canopies: structural and functional properties

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

Canopies under stress

Light intensity, light quality and availability of water

3Canopies under stress

How are these functional and structural properties influenced by stress?

How can we quantify stress effects on function and structure?

4

Morphological traits of wheat as related to water supply


0 100 200 3000

5

10

15

20

25

30

35

Flag leaf length (cm)

Leaf angle (°)

Irrigation (mm)

Flag

leaf

leng

th, l

eaf a

ngle

0 100 200 3000

1

2

3

4

5

6

Flag leaf

Third leaf

Irrigation (mm)

Spec

ific l

eaf w

eigh

t (m

g cm

-2)

after data fom Zhang et al. 2011

5

Simulated diurnal time course of net canopyphotosynthesis 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)′

Hammer et al. 2009Canopies under stress

6

Simulated effects of increasing and decreasing leaf angle by 30 % on light extinction coefficient and Light interception of tomato canopies

Canopy light interception: 78%Light extinction coefficient: 0.60±0.02

Canopy light interception: 49%Light extinction coefficient 0.27±0.01

Canopies under stress Chen et al. 2014, J. exp. Bot., accepted

130% 70%

7

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

Flexas et al. 2012Canopies under stress

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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 hetero-geneities of light inside a canopy


10

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).

Song et al. 2013Canopies under stress

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Functions

Structure

Environment

Spatially explicit models of canopies: Functional-structural plant models (FSPM)

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


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Functions

Structure

Environment

Dynamic cucumber architecture model


13

The virtual 2 m cucumber canopy with 18 plants, constructed using digitized data in GroIMP, in top view (A) and side view (B).

Chen et al. 2014; doi:10.1093/aob/mcu100Canopies under stress

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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 ….


16

Simulated leaf photosynthesis rate under 100 % direct light and 100 % diffuse light in a cucumber canopy


17

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


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Chloroplastic CO2 concentration (mol mol-1)

50 100 150 200 250 300 350

Pho

tosy

nthe

sis

(m

ol C

O2

m-2

s-1

)

0

5

10

15

20

25

30

35

J = Jref

J = Jmax

J

Reference photosynthesis rate

Current photosynthesis rate

Diffusional limitation

Biochemical limitation

Light limitation

Current CO2 conc.

Calculation of photosynthetic limitations due to biochemical, light and diffusional factors


19

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)


20Canopies under stress Chen et al. 2014; doi:10.1093/aob/mcu100

21

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.


22

Simulated effects of drought stress (soil water potential - 0.4 MPa) on photo-synthesis rates at different positions in a cucumber canopy

Non-stress

Light interception (mol photon plant-1 s-1)

0 200 400 600

Pho

tosy

nthe

sis

rate

(m

ol C

O2

plan

t-1

s-1 )

0

2

4

6

8

10

12

14

16

18


Drought stress


0 200 400 600

Pho

tosy

nthe

sis

rate

(m

ol C

O2

plan

t-1

s-1 )

0

2

4

6

8

10

12

14

16

18

23

Simulated effects of drought stress (soil water potential - 0.4 MPa) on light use efficiencies at different positions in a cucumber canopy Drought stress


0 200 400 600

Ligh

t us

e ef

ficie

ncy

(m

ol C

O2

mol

-1 p

hoto

n)

0.00

0.01

0.02

0.03

0.04

0.05

Non-stress


0 200 400 600

Ligh

t us

e ef

ficie

ncy

(m

ol C

O2

mol

-1 p

hoto

n)

0.00

0.01

0.02

0.03

0.04

0.05


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Canopy part

upper middle-upper

middle-lower lower whole

plantMaximum Ac (µmol plant-1 s-1)

Non-stress 5.9 4.3 3.9 1.6 15.6Drought 5.1 3.7 3.4 1.5 13.7

Maximum LUEc (µmol CO2/µmol PAR)


Ic for maximum LUEc (µmol plant-1 s-1)


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


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Light interception

Osmotic stress

Ionic stress(ion accumulation)

Organ size

red.

Stom. conduct.

red.

red.

PhotosynthesisTranspiration

Ion accumulation

What happens under salinity?

Toxic

Biochemicalcapacity

Ligh

t us

e effi

cien

cy

Non-architectural effects

Architectural effects


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Salinity level (mM NaCl in nutrient solution)

0 20 40 60 80

Sho

ot d

ry m

ass

(% o

f co

ntro

l)

60

70

80

90

100

110

Low temperatureHigh temperature

y = 100 -0.49xR2 = 0.99

y = 100 -0.34xR2 = 0.91

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


27

Relative light use efficiency at three salinity levels under low (LT, 22/18°C) and high (HT, 32/28°C) day/night temperature conditions

40 mM 60 mM 80 mM Day LT HT LT HT LT HT29-35 1.17 1.07 0.96 0.93 0.80 0.8136-43 1.10 1.06 0.88 0.91 0.69 0.7844-50 1.05 1.02 0.85 0.86 0.68 0.7351-56 1.07 1.02 0.86 0.85 0.66 0.7257-63 0.97 0.93 0.78 0.79 0.64 0.6764-70 1.05 1.05 0.73 0.89 0.66 0.7571-77 0.93 0.96 0.75 0.83 0.61 0.71


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30 40 50 60 70 80 90

Arc

hite

ctur

al e

ffec

ts o

n sh

oot

dry

mas

s (%

of

cont

rol)

60

70

80

90

100

110

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


0 20 40 60 80

Sho

ot d

ry m

ass

(% o

f co

ntro

l)

60

70

80

90

100

110

Low temperatureHigh temperature


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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


30

Thank you!


plant canopies under drought stress– structures, functions, (genes) and models

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