1 Global carbon balance Global carbon balance GPP Gross primary production CO 2 area -2 time -1 Net primary production = Gross primary production – autotrophic respiration CO 2 area -2 time -1 Global carbon balance Global carbon balance Net ecosystem production = Gross primary production – total respiration CO 2 area -2 time -1 Gross primary production CO 2 area -2 time -1
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Global carbon balance Global carbon balance GPP
Gross primary production CO2 area-2 time-1
Net primary production = Gross primary production – autotrophic respiration
CO2 area-2 time-1
Global carbon balance Global carbon balance
Net ecosystem production = Gross primary production – total respiration
CO2 area-2 time-1
Gross primary production CO2 area-2 time-1
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Major controls over GPP
• Quantity of leaf area • Length of photosynthetic season • Photosynthetic rate of individual leaves
Photosynthetic capacity Environmental stress
Major controls over Rtotal
• Large amount of uncertainty
Net ecosystem production = Gross primary production – total respiration
CO2 area-2 time-1
Major controls over Rplant
• Large amount of uncertainty
• Quantity of tissue mass
Major controls over Rplant
• Quantity of tissue mass • Temperature
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Temperature 10 k2
T2 – T1 k1 Q10 = ln
Chamaecyparis obtusa
Vaccinium myrtillus Major controls over Rplant
• Quantity of tissue mass • Temperature • Growth rate
What controls respiration at tissue level (per gram tissue)?
R = R + R +R plant growth maint ion
Growth Maintenance Ion transport
R/w = g(dw/dt)/w + m
Functional model of respiration
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Pinto bean
Carbon cost of growth is similar among species and plant parts
What controls maintenance respiration?
• Plant chemistry – especially protein content
• Environment – especially temperature and drought
What controls respiration at tissue level (per gram tissue)?
R = R + R +R plant growth maint ion
Growth Maintenance Ion transport
Major controls over Rplant
• Quantity of tissue mass • Temperature • Growth rate • Nitrogen
Nitrogen Soybean
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Major controls over Rplant
• Quantity of tissue mass • Temperature • Growth rate • Nitrogen
Major controls over Rplant
• Quantity of tissue mass • Temperature • Growth rate • Nitrogen • Other
Glycolysis • occurs in the cytoplasm • absence of O2 • oxidizes glucose to pyruvate
• requires energy to start
• generates small amount of ATP
Citric acid cycle • aerobic • occurs in mitochondrion • cyclic
• acetyl-CoA oxidized • produces CO2
• ATP • NADH • FADH2
Central Metabolic Pathwaymeta
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Electron transport system Summary of ATP production
Other considerations: Sugar, Starch concentrations Light versus dark Canopy Position Injury Atmospheric CO2
Alternative oxidase
Skunk cabbage Titan arum
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Net primary production = Gross primary production – autotrophic respiration
CO2 area-2 time-1
NPP is about half of GPP
Boreal
Pacific Northwest
Temperate Coniferous
Temperate Deciduous
Temperate MixedTropical
CUE
0.0
0.2
0.4
0.6
0.8
a
a
b
bcab
ab
Forest age (log years)0.5 1.0 1.5 2.0 2.5 3.0
CU
E
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
What is Net Ecosystem Production (NEP)?
• Rate of carbon accumulation in an ecosystem – Balance between carbon inputs and outputs – Small difference between two large fluxes
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What is Net Ecosystem Production (NEP)?
• Rate of carbon accumulation in an ecosystem
NEP = GPP - (R + R + F + F ) plant heterotr disturb leach
NEP is the balance between two large fluxes GPP and ecosystem respiration NEP = GPP - Recosystem
Ecosystem Carbon Balance
Recosystem = Rplant + Rheterotrophs
Rheterotrophs = Rmicrobes + Ranimals
Recosystem = (50%)Rplant + (50%)Rhet.
Rheterotrophs = (90%)Rmicrobes + (10%)Ranimals
Net primary production = Gross primary production – autotrophic respiration
Net ecosystem production = Gross primary production – total respiration
Eddy Covariance
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Eddy Covariance Network
Valentini
Biome differences in NEE reflect large net carbon loss by respiration at high latitudes
Why is NEE positive in most ecosystems?
• Maybe all ecosystems accumulate C between disturbances
• Maybe bias in site selection – Researchers prefer productive sites?
• Maybe carbon loss by leaching is significant • Maybe terrestrial biosphere is gaining carbon
– due to elevated CO2 and N deposition
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