Transcript Document

Month
Aug.
Sept.
Day
26
28
2
4
9
11
16
18
23
Topic
Introduction
The ecosystem concept
Climate/soils
Soils II
Ecosystem energy
balance
Water cycling
Carbon
GPP/NPP
NEP
C,M&M
1
2
3
4
4
5
6
6
Atmospheric Carbon Dioxide
Tons of CO2-C emitted per person per
year
Anthropogenic C Emissions: Land Use Change
Carbon Emissions from Tropical Deforestation
2000-2006
1.5 Pg C y-1
1.60
Africa
1.40
Latin America
1.20
S. & SE Asia
1.00
SUM
(16% total emissions)
0.80
0.60
0.40
0.20
Houghton, unpublished
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
1900
1890
1880
1870
1860
0.00
1850
Pg C yr-1
1.80
Carbon
Biosphere has large effect on
atmospheric CO2 concentrations
Photosynthesis is the primary energy base
for all terrestrial ecosystems
Net Primary Productivity (NPP) =
Gross Primary Productivity (GPP) – RespirationPlant
Plant growth = Photosynthesis - Respiration
Ecosystem Carbon Cycling
Net Ecosystem Production (NEP) = GPP - REcosys
Recosys= Respiration of plants, animals, and soil
microbes, plus other C transfers from plants
Positive NEP; GPP > Recosys;
ecosystem is removing C from the atmosphere = C sink
Negative NEP; GPP < Recosys;
ecosystem is releasing C to the atmosphere = C source
Political Implications of Ecosystem
Carbon Cycling
Kyoto Protocol to the UN Framework Convention on
Climate Change: international treaty on greenhouse gas
emissions (incld. CO2)
Negotiated 1997
Came into force 2004 (Russia and the “55% clause”)
Now 161 counties, ~61% emissions
EU (Annex 1): ratified protocol, submit annual gas
inventory; reduce emissions to 5% below 1990,
effectively 15% below projected rates for 2008
Developing countries (Non-annex 1) can choose to
reduce emissions and sell reductions to Annex 1 as
carbon credits (“cap and trade”)
Review of C3 Photosynthesis
In the chloroplast, light reactions
transform light energy into
chemical energy
Photosynthetically active radiation (PAR) absorbed by
chlorophyll (APAR) between 400-700 nm
Electrons derived from oxidation of H2O to O2 used to
make high-energy ATP, NADPH
Review of C3 Photosynthesis
Dark reaction use chemical energy (ATP, NADPH) to
fuel carbon fixation reaction (Calvin cycle).
CO2 is used to carboxylate ribulose bisphosphate
(RuBP) with the enzyme ribulose bisphosphate
carboxylase/oxygenase (Rubisco)
Rubisco accounts for ≈ 25% of leaf Nitrogen
Other Ps enzymes account for ≈ 25% of leaf N
Carboxylation of RuBP produces 2, 3-C sugars
Review of C3 Photosynthesis
Rubisco can also oxygenate RuBP, ultimately losing
CO2 through photorespiration
20-40% of energy from Ps immediately lost via
photorespiration
Depends on relative concentrations of O2 and CO2 in
leaf, temperature
Net Ps: difference between tot. Ps and
photorespiration=GPP
C4, CAM use same biochemistry, but different timing
and morphology to affect O2/CO2 ratio in leaf
Limitation
Plants adjust components of Ps so physical and
biochemical processes co-limit C fixation
Plants adjust resource acquisition to maximize
capture of the most limiting resource
• CO2
• Water
Acclimation versus adaptation!
• Light
• Nitrogen
• [Temperature-modulator]
CO2 response curve of photosynthesis
• Diffusion limitation affected by stomata
• Biochemical limitation affected by light/enzymes
• Plants equalize physical and biochemical
limitations
Inherent tradeoff between CO2 gain and H2O loss
Water availability
• Limits full use of light in arid conditions due to
tradeoff with CO2
• Water Use Efficiency (WUE)
Lo H2O ecosystems
Lo stomatal conductance
Lo leaf area, deciduousness
Steep leaf angels
Reflective leaves
Small leaves
C4, CAM
Deep roots
Light response curve of photosynthesis
• Light limitation slope (quantum yield) constant for C3
• Light saturation limited by investment in enzymes (N)
• Photoinhibition results from damaged membranes
Light variation in ecosystems
Lecture ended here
Light environment
• …for individual leaves, it is determined by
total leaf area above
• Penetration of light into the canopy depends
on leaf angles and distribution in space
• Acclimation and adaptation to light
environment
• Light Use Efficiency (LUE)
Leaf nitrogen determines Ps capacity
Rubisco accounts for ≈ 25% of leaf Nitrogen
Other Ps enzymes account for ≈ 25% of leaf N
Nitrogen availability
• Inherent tradeoff between traits that favor high
Ps and traits that favor retention of N
• Easier for a plant to retain N then to acquire from
the environment
Low N ecosystem
Increased leaf toughness
Increased structural C
Thick leaves (high weight/area)
Increased leaf life span
Increased defense (herbivory)
Low Ps (per unit weight)
High N ecosystem
Decreased leaf toughness
Decreased structural C
Thin leaves (low weight/area)
Decreased leaf life span
High Ps (per unit weight)
Temperature extremes
• Plants minimize effects of lo T by increasing Ps
capacity (increasing leaf N)
• Minimize effects of hi T by
• hi stomatal conductance (Hi H2O)
• dissected, reflective, deciduous leaves (Lo H2O)