Photosynthesis and Environment
Leaf and Canopy Aging
Environmental Plant Physiology
Photosynthesis - Aging
Goals and Learning Objectives:
krreddy@Ra.MsState.edu
Department of Plant and Soil Sciences
Senescence, Aging and Death and Agriculture
¾ Senescence, aging, and death – conceived in the past
as inevitable, negative processes (wear and tear
phenomenon), but now considered as an internal part
of differentiation and development.
¾ Leaf senescence is one of the most conspicuous
processes that has been studied in the context of plant
aging and senescence.
¾ The terminal phase of leaf development cannot be
described simply as a collection of passive and
deteriorative processes during which gradual decline
in vital systems takes place.
• To understand the effects of leaf and canopy aging
on photosynthesis process at leaf and canopy
level.
¾
Photosynthesis and leaf-level aging.
¾
Photosynthesis and canopy-level aging.
Senescence, Aging and Death and Agriculture
¾ Extensive physiological and biochemical studies in the
last few decades on leaf senescence have suggested
that it is highly regulated and active process, which is
characterized by differential and sequential changes in
almost every sub-cellular compartment.
¾ Leaf aging or senescence has implications on
agriculture, affecting crop yield and the shelf life of
leafy vegetables.
Leaf and canopy development and aging process
Leaf
5-day
12-day
2-day
Emerging leaf
8-day
Canopies
Emergence
Squaring
Photosynthesis - Aging
Leaf Level
Flowering
About to abscise
Mature crop
1
Photosynthesis - Aging
Leaf Level
Photosynthesis - Aging
Leaf Level
Deep Inside
Deep Inside
Unfolding
leaf
Mature
leaf
Chloroplasts
with limited
thylakoid
development
Chloroplasts contain chlorophyll and
proteins, and these are the centers of
photosynthesis. As leaves grow in size,
these centers of photosynthesizing
chloroplasts develop very well-defined
thylakoids for optimum photosynthesis.
Proteins and pigments that function in the
photochemical events of photosynthesis
are part of the thylakoid.
Chloroplasts
with welldeveloped
thylakoid
Photoynthesis and Light Response Curves
Aging - Photosynthetic Light-response Curves
for Cotton Leaves
Photosynthesis, µmol CO2 m-2 s-1
50
Photosynthesis, µmol m
-2 -1
s
Maximum net photosynthesis
40
LUE
30
20
Light
Carboxylation
Limited
Limited
10
0
LCP where Pn = 0
40
30
500
Respiration
1000
1500
-2
-1
PPFD, µmol m s
27 days
25
20
15
35 days
10
40 days
5
0
0
-10
0
20 days
35
800
1200
1600
2000
2400
PPFD, µmol m-2 s-1
Light saturation point
Leaf Aging and Photosynthesis
-2
40
Photosynthesis, µmol CO2 m s
-1
Leaf Aging and Photosynthesis
Photosynthesis, µmol CO2 m-2 s-1
400
2000
30/22°C and 360 µl l-1 CO2
35
30
25
20
15
10
5
0
0
10
20
30
Leaf Age, d
40
50
60
50
PPFD = 1500 µmol photon m-2 s-1
40
30
20
10
0
15
20
25
30
35
40
Leaf Age, days
45
50
2
Leaf Aging - Photosynthestic Parameters
Expressed as Fraction of Maximum (= 20 d)
1.5
0.04
0.03
1.0
0.02
Conductance
0.5
0.01
0.00
15
20
25
30
35
40
Leaf Age, days
0.0
50
45
1.5
1.0
Photosynthesis
0.5
0.0
Conductance
15
Photosynthesis, mg CO2 m-2 s-1
5
Leaf N, %
4
3
2
20
25
30
35
40
Leaf Age, days
45
50
5
4
3
2
1
0
2
3
Leaf N, %
4
5
5
Starch
30
6
25
5
20
Carotenoids
4
15
45
3
50
4
1.6
Sugars, %(w/w)
7
Carotenoid, µg cm-2
Chlorophyll
Chlorophyll, µg cm-2
50
2.0
35
30
35
40
Leaf Age, days
45
6
8
25
30
35
40
Leaf Age, days
Leaf Aging - Starch and Sugars
40
20
25
7
1
Leaf Aging - Leaf Pigments
Chlorophyll and Carotenoids
10
15
20
Photosynthesis - Leaf Nitrogen
Leaf Aging and Leaf Nitrogen
1
15
Light Utilization Efficiency
3
1.2
2
Sugars
0.8
1
0.4
0.0
15
Starch %(w/w)
0.05
2.0
Light Utilization Efficiency
Fraction of Maximum
0.06
Conductance, mol H2O m-2 s-1
LUE, µmol CO2 µmol-1 photon
Leaf Aging and Light Utilization Efficiency
and Conductance
0
20
25
30
35
40
Leaf Age, days
45
50
3
Leaf Aging and Photosynthesis
Leaf Aging and Photosynthesis
¾ As leaves grow in size, leaf net photosynthesis increases rapidly
from leaf unfolding (about zero at leaf unfolding) until the leaf
reaches its potential maximum size. Soon thereafter (from about 20
days from unfolding), leaf net photosynthesis declines linearly.
Light saturation occurs at lower light levels as leaves age.
¾ The onset (from about 20 days) and magnitude (rates) of declines in
leaf conductance and light utilization efficiencies are closely
coupled with leaf maximum photosynthesis rates.
¾ Leaf transpiration rates closely followed photosynthetic rates
throughout the leaf development.
¾ Leaf pigments (chlorophylls and carotenoids) decline from about 35
days from leaf unfolding, at least in cotton.
Leaf Aging and Photosynthesis
¾ The concentration of CO2 inside the leaf (Ci), and the number of
chloroplasts in the mesophyll remain nearly constant during the
aging process, except in the oldest leaves that are about to abscise.
¾Total leaf protein content, RuBP carboxylase and electron transport
activity decline parallel to photosynthesis during the aging process.
¾ Leaf N also declines from about 20 days, but the decline was not as
dramatic as the photosynthetic parameters.
¾ The levels of starch and sugars also decrease during the aging
process suggesting the loss of photosynthetic activity.
¾ Therefore, the physiological deterioration of leaf photosynthetic
activity during the aging process may be more related to declining
Rubisco protein (photosynthetic capacity) and photosynthetic
efficiency (LUE) than to leaf N, leaf pigments and number of
chloroplasts. The leaf N and pigments also play a role at a latter stage.
Leaf Aging and Photosynthesis
The shape and magnitude of photosynthetic capacity and efficiency
did not change due to leaf location or position when measured at the
same age, at least in cotton.
Varying light levels during
aging by partial shading the
leaf did not change leaf
photosynthetic
characteristics (LUE and
Pmax.).
Photosynthesis, µmol CO2 m-2 s-1
Leaf Aging and Photosynthesis
40
30/22°C and 360 µl l-1 CO2
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
Leaf Age, d
Leaf Aging and Photosynthesis
¾ In cotton, Pmax is out of sequence
with carbon requirements of bolls:
1. Mainstem leaves reach peak rates
several days before flowering on
the branch and rates are
substantially reduced during bollfilling.
2. The branch leaves subtending
flower/boll reach maximum
photosynthesis (Pmax) about the
time of anthesis.
Mainstem leaf
Branch leaf
Flower-bud
Photosynthesis - Aging
Canopy Level
3. Carbon appears to be translocated
from remote sites to the
developing bolls.
4
Leaf and canopy development and aging process
Leaf
Canopy Photosynthesis, mg CO2 m-2 s-1
5-day
12-day
Photosynthesis and Light Response Curves
Canopies
Emergence
Emerging leaf
2-day
8-day
Squaring
Flowering
About to abscise
4
Maximum net photosynthesis
3
LUE
2
1
Light
Carboxylation
Limited
Limited
0
Light saturation point
LCP where Pn = 0
-1
Mature crop
0
500
Respiration
7
6
1995 ambient Temp.
PPFD 1200 µmole m-2 s-1
5
4
3
2
1
Open Boll
Flower
360 CO2
0
20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Days after Emergence
1500
2000
Photosynthesis - Canopy Growth and Aging
Canopy Light Utilization Efficiency
0.020
Canopy Light Utilization Efficiency
(µmol CO2 µmol-1 photons)
Photosynthesis, mg CO2 m-2 s-1
Canopy Aging - Photosynthesis
1000
PPFD, µmol m-2 s-1
0.018
N - Sufficient
0.016
0.014
0.012
0.010
0.008
0.006
0.004
Flowering
0.002
0.000
20
30
40
50
60
Boll opening
70
80
90
100 110 120 130 140
Days after Emergence
Ptotosynthesis - Canopy Growth and Aging
Canopy Conductance
Canopy Conductance, mm s-1
20
18
N - Sufficient
16
14
12
Photosynthesis - Aging
10
Factors controlling aging and
photosynthetic process
8
6
4
Flowering
Boll opening
2
0
20
30
40
50
60
70
80
90
100 110 120 130 140
Days after Emergence
5
Boll-load and Vegetative Growth
Stem Elongation vs Boll Numbers
7
PPFD 1200 µmole m-2 s-1
6
1995 ambient Temp.
720 CO2
5
4
3
2
1
Open Boll
Flower
360 CO2
0
5
Stem Elongation, cm plant-1 d-1
Photosynthesis, mg CO2 m-2 s-1
Canopy Aging - Photosynthesis
Response to Carbon Dioxide
Linear, y = 3.4 - 0.105 * X, r ² = 0.86
4
3
2
1
0
20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Days after Emergence
0
100
80
60
40
20
0
20 30 40 50 60 70 80 90 100 110 120 130 140 150
Canopy Photosynthesis, mg CO2 m-2 s-1
Net Photosynthesis, g CO2 m-2 d-1
120
25
30
35
7
N-Sufficient
N-deficient treatment imposed
6
5
4
3
2
Flowering
Boll opening
N-Deficient
1
0
20
30
40
50
60
70
80
90 100 110 120 130 140 150
Days after Emergence
Canopy Aging and Photosynthesis
Canopy Light Utilization Efficiency
Canopy Aging and Canopy Conductance
Response to Nitrogen Nutrition
20
0.020
Day of N-deficient treatment
N - Sufficient
0.016
0.012
0.008
Flowering
Boll opening
N - Deficient
0.000
20 30 40 50 60 70 80 90 100 110 120 130 140
Days after Emergence
Canopy Conductance, mm s-1
Canopy Light Utilization Efficiency
(µmol CO2 µmol-1 photon)
20
8
Days after Emergence
0.004
15
Canopy Growth - Aging - Seasonal Trends
Response to Nitrogen Nutrition
160
1995 Ambient Temp.
10
Bolls, no. plant-1
Canapy Growth - Aging - Daily Net Photosynthesis
Seasonal Trends1995
140
5
N-deficient treatment imposed
18
N - Sufficient
16
14
12
10
8
6
4
Flowering
Boll opening
2
0
20
N - Deficient
30
40
50
60
70
80
90
100 110 120 130 140
Days after Emergence
6
Photosynthesis, mg CO2 m-2 s-1
Photosynthesis - Growth - Aging
Response to Water Deficits
9
8
Well-watered
7
6
Photosynthesis - Aging
5
4
Canopy level – other species - soybean
3
2
Trt. Start date
Water stressed
1
0
55
Rewatered
60
65
70
75
80
85
90
Days after Emergence
Canopy Aging and Photosynthesis
Soybean
Photosynthesis - Aging
Canopy level – other species
Indeterminate vs. determinate plant types
Canopy Photosynthesis, mg CO2 m-2 s-1
Canopy Aging - Photosynthesis
Species or Plant type Variation
Canopy Aging and Photosynthesis
10
9
¾ Aging process at the canopy level appears to be a function
of leaf-level processes, but modulated by nutrient
supply/demand which in turn affects growth and
development of various organs including the younger and
more efficient leaves produced at the top of the canopy.
Indeterminate Crop: Cotton
Elevated CO2
8
7
6
5
¾ Sustained photosynthetic efficiency and capacity of
canopies require optimum environmental conditions
(water, nutrients, including carbon), to continually initiate
new leaves.
4
3
2
Flowering
Determinate Crop: Sorghum
1
0
0
20
40
60
80
Days after Emergence
100
120
140
¾ Any management or environmental factor that limits
photosynthesis capacity and efficiency can potentially limit
crop yield.
7