中科院 生态系统水碳氮循环与通量观测原理与技术
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Chap. 5 33
Vegetation maintains relatively constant LUE
• Leaf level regulation
– Balance biochemical and physical limitations to photosynthesis
• Canopy level regulation
– Converts light into chemical energy
• Carbon fixation reactions
– Uses chemical energy to convert CO2 into sugars
Chap. 5
9
Chap. 5
10
Rubisco can gain or lose carbon
Chap. 5 24
Causes of light variation in ecosystems
Chap. 5
25
Mechanisms of adjusting to variation in light
• Light response curve (almost instantaneous) • Acclimation (physiological adjustment)
• Adjustment of photosynthetic capacity to soil resources • Adjustment of stomatal conductance • Adjustment of leaf area • Change in species composition
• Carboxylase
– Reacts with CO2 to produce sugars – Leads to carbon gain
• Oxygenase
– Reacts with oxygenase to convert sugars to CO2 – Respires 20-40% of fixed carbon – Photo-protection mechanism
Chap. 5
3
Gross Primary Production (GPP)
• Net photosynthesis at the ecosystem scale
Chap. 5
4
GPP is C input to the ecosystem
Chap. 5
5
Photosynthesis
• Levels of control
Chap. 5
22
Light response curve of photosynthesis
Chap. 5
23
Light use efficiency
• Efficiency of using light to fix carbon
– Same thing as light response curve
• Nearly constant in C3 plants at low light (about 6%)
– i.e., linear portion of light response curve is same in all plants – Known as quantum yield of photosynthesis
• Light limitation • Enzyme limitation
Chap. 5
20
CO2 response curve of photosynthesis
Chap. 5
21
3.2 Light Limitation
• Leaves adjust stomatal conductance and photosynthetic capacity to maximize carbon gain in different light environments.
– Sun leaves (produce new leaves)
• More cell layers • Higher photosynthetic capacity
– Shade leaves
• More light-harvesting pigments
• Adaptation (genetic changes)
Chap. 5
17
How homoihydric plants can live in very dry places: CAM photosynthesis
Chap. 5
18
3. Net Photosynthesis by Individual Leaves
Chap. 5
19
3.1 Basic principle of environmental control
Chap. 5
41
Leaf longevity is a major factor determining photosynthetic capacity Inevitable tradeoff between photosynthesis and leaf longevity Long-lived leaves contain lots of non-photosynthetic compounds Herbivore protection Desiccation resistant
– Controls in individual leaves – Control by canopy processes
• Controlling factors
– Direct controls: light, CO2 – Indirect controls: water, nutrients
Chap. 5
• Equalize physical and biochemical limitations of photosynthesis
– Physical limitation: diffusion of CO2 to leaf
• Boundary layer • Stomatal opening
– Biochemical limitation: carboxylation rate
– Maintain highest Ps capacity at top of canopy – Shed leaves that don’t maintain positive carbon balance
Chap. 5
34
3.3 Direct Controls
Chap. 5
35
Chap. 5
Chapter 5 Carbon Input to Terrestrial Ecosystems
Part II Mechanisms Chapin, Matson, Mooney Principles of Terrestrial Ecosystem Ecology
Chap. 5
1
1. Introduction
Chap. 5 38
Leaf nitrogen determines photosynthetic capacity
Chap. 5
39
Chap. 5
40
Stomatal conductance adjusts to match photosynthetic capacity (or vice versa)
Chap. 5
30
Leaf area determines light environment
• Light declines exponentially wiwenku.baidu.comhin canopy
Chap. 5
31
Species that are adapted to growing at reduced light intensities, which are referred to as shade tolerant species (e.g. sugar maple, hemlock, beech), generally have lower compensation points and levels of light saturation than shade intolerant species like the aspens and many pines.
36
Some plants alter photosynthetic capacity in response to changes in CO2
Chap. 5
37
Vegetation adjusts photosynthetic capacity and leaf area to balance availability of soil resources
– Leaf angle – Leaf movements – Efficient use of sun flecks
Chap. 5
29
Multiple species increase range of light levels over which light use efficiency remains constant
6
Over long time scales (a year) indirect controls predominate
Chap. 5
7
2. photosynthetic pathways
Chap. 5
8
Two major sets of reactions
• Light-harvesting reactions
Chap. 5
2
Carbon inputs to ecosystems
• Process: photosynthesis • Importance
– Energy that drives all biotic processes – Accounts for half of organic matter on Earth
Chap. 5 11
Chap. 5
12
Chap. 5
13
3 photosynthetic pathways
• C3 photosynthesis • 2 other pathways (see textbook)
Chap. 5
14
Chap. 5
15
Chap. 5
16
Creates high conc of CO2
Chap. 5
32
Shade intolerant species saturate at relatively high levels of photon flux density, while shade tolerant species saturate at relatively low levels of photon flux density.
Chap. 5
28
Mechanisms of adjusting to variation in light
• Other neat tricks
– Maximize leaf area
• More leaves • Thin leaves (shade) or cylindrical leaves (sun)
Chap. 5
42
Suite of traits that influence carbon gain
• Growth rate
– Depends on availability of soil resources
• • • •
Leaf longevity Leaf nitrogen concentration Photosynthetic capacity Inevitable tradeoff between leaf longevity and photosynthesis Chap. 5
– Mechanisms same as for acclimation
Chap. 5 26
Chap. 5
27
Left-hand side: sun and shade leaves of maple top-right: leguminous tree of arid regions bottom-right: extreme shade-adaptation in the lower part of the rain forest (focusing cells, very large substomatal cavity)
Vegetation maintains relatively constant LUE
• Leaf level regulation
– Balance biochemical and physical limitations to photosynthesis
• Canopy level regulation
– Converts light into chemical energy
• Carbon fixation reactions
– Uses chemical energy to convert CO2 into sugars
Chap. 5
9
Chap. 5
10
Rubisco can gain or lose carbon
Chap. 5 24
Causes of light variation in ecosystems
Chap. 5
25
Mechanisms of adjusting to variation in light
• Light response curve (almost instantaneous) • Acclimation (physiological adjustment)
• Adjustment of photosynthetic capacity to soil resources • Adjustment of stomatal conductance • Adjustment of leaf area • Change in species composition
• Carboxylase
– Reacts with CO2 to produce sugars – Leads to carbon gain
• Oxygenase
– Reacts with oxygenase to convert sugars to CO2 – Respires 20-40% of fixed carbon – Photo-protection mechanism
Chap. 5
3
Gross Primary Production (GPP)
• Net photosynthesis at the ecosystem scale
Chap. 5
4
GPP is C input to the ecosystem
Chap. 5
5
Photosynthesis
• Levels of control
Chap. 5
22
Light response curve of photosynthesis
Chap. 5
23
Light use efficiency
• Efficiency of using light to fix carbon
– Same thing as light response curve
• Nearly constant in C3 plants at low light (about 6%)
– i.e., linear portion of light response curve is same in all plants – Known as quantum yield of photosynthesis
• Light limitation • Enzyme limitation
Chap. 5
20
CO2 response curve of photosynthesis
Chap. 5
21
3.2 Light Limitation
• Leaves adjust stomatal conductance and photosynthetic capacity to maximize carbon gain in different light environments.
– Sun leaves (produce new leaves)
• More cell layers • Higher photosynthetic capacity
– Shade leaves
• More light-harvesting pigments
• Adaptation (genetic changes)
Chap. 5
17
How homoihydric plants can live in very dry places: CAM photosynthesis
Chap. 5
18
3. Net Photosynthesis by Individual Leaves
Chap. 5
19
3.1 Basic principle of environmental control
Chap. 5
41
Leaf longevity is a major factor determining photosynthetic capacity Inevitable tradeoff between photosynthesis and leaf longevity Long-lived leaves contain lots of non-photosynthetic compounds Herbivore protection Desiccation resistant
– Controls in individual leaves – Control by canopy processes
• Controlling factors
– Direct controls: light, CO2 – Indirect controls: water, nutrients
Chap. 5
• Equalize physical and biochemical limitations of photosynthesis
– Physical limitation: diffusion of CO2 to leaf
• Boundary layer • Stomatal opening
– Biochemical limitation: carboxylation rate
– Maintain highest Ps capacity at top of canopy – Shed leaves that don’t maintain positive carbon balance
Chap. 5
34
3.3 Direct Controls
Chap. 5
35
Chap. 5
Chapter 5 Carbon Input to Terrestrial Ecosystems
Part II Mechanisms Chapin, Matson, Mooney Principles of Terrestrial Ecosystem Ecology
Chap. 5
1
1. Introduction
Chap. 5 38
Leaf nitrogen determines photosynthetic capacity
Chap. 5
39
Chap. 5
40
Stomatal conductance adjusts to match photosynthetic capacity (or vice versa)
Chap. 5
30
Leaf area determines light environment
• Light declines exponentially wiwenku.baidu.comhin canopy
Chap. 5
31
Species that are adapted to growing at reduced light intensities, which are referred to as shade tolerant species (e.g. sugar maple, hemlock, beech), generally have lower compensation points and levels of light saturation than shade intolerant species like the aspens and many pines.
36
Some plants alter photosynthetic capacity in response to changes in CO2
Chap. 5
37
Vegetation adjusts photosynthetic capacity and leaf area to balance availability of soil resources
– Leaf angle – Leaf movements – Efficient use of sun flecks
Chap. 5
29
Multiple species increase range of light levels over which light use efficiency remains constant
6
Over long time scales (a year) indirect controls predominate
Chap. 5
7
2. photosynthetic pathways
Chap. 5
8
Two major sets of reactions
• Light-harvesting reactions
Chap. 5
2
Carbon inputs to ecosystems
• Process: photosynthesis • Importance
– Energy that drives all biotic processes – Accounts for half of organic matter on Earth
Chap. 5 11
Chap. 5
12
Chap. 5
13
3 photosynthetic pathways
• C3 photosynthesis • 2 other pathways (see textbook)
Chap. 5
14
Chap. 5
15
Chap. 5
16
Creates high conc of CO2
Chap. 5
32
Shade intolerant species saturate at relatively high levels of photon flux density, while shade tolerant species saturate at relatively low levels of photon flux density.
Chap. 5
28
Mechanisms of adjusting to variation in light
• Other neat tricks
– Maximize leaf area
• More leaves • Thin leaves (shade) or cylindrical leaves (sun)
Chap. 5
42
Suite of traits that influence carbon gain
• Growth rate
– Depends on availability of soil resources
• • • •
Leaf longevity Leaf nitrogen concentration Photosynthetic capacity Inevitable tradeoff between leaf longevity and photosynthesis Chap. 5
– Mechanisms same as for acclimation
Chap. 5 26
Chap. 5
27
Left-hand side: sun and shade leaves of maple top-right: leguminous tree of arid regions bottom-right: extreme shade-adaptation in the lower part of the rain forest (focusing cells, very large substomatal cavity)