Terrestrial Carbon Process

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Lecture 34 Terrestrial Carbon Process I.
Photosynthesis and respiration (revisit) II.
Carbon Stocks and Fluxes in Terrestrial
Ecosystems III. Terrestrial Ecosystems A.
Ecosystem Concept B. Ecosystem Carbon Balance
(GPP, NPP, NEP, NBP) VI. Missing carbon sinks?
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Lecture 3 Photosynthesis and Respiration
Photosynthesis Overview
1. What is the Photosynthesis?
2. Where the Photosynthesis Occurs?
3. How Photosynthesis works? Key Processes
4. Alternative Photosynthesis Pathway
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1. What is the Photosynthesis?
Photosynthesis is the biogeochemical process by
which Plants cover atmospheric CO2 to carbon
productions that results in plant growth
We express this combined knowledge as the
photosynthetic equation 6CO2 12H2O light
energy ---gt C6H12O6 6O2 6H2O (or CO2 2H2O
light energy ---gt CH2O O2 H2O)
? is the conversion of light-energy to
chemical-energy via the chloroplasts
? generates 170 billion metric tons of sugar
annually, which enters our biosphere
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2. Where the Photosynthesis Occurs?

• Photosynthesis takes place within leaf (or green
  stem) cells containing chloroplasts
• e.g. each cell contains 40 to 50 chloroplasts
• a chloroplast has dozens of the thylakoids
  and millions of pigment molecules
• each thylakoid contains thousands of
  photosystems

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3. How Photosynthesis works? key processes
Photosynthetic Overview
A. There are three basic steps in
photosynthesis (1) Light Reactions -
energy capture (2) Dark Reactions -
fixation of carbon (3) Pigment Regeneration
electron replacement from the splitting of H2O
in oxygenic photosynthesis.
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C3 photosynthesis ( three-carbon sugars) C3
plant
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4. Alternative Photosynthetic Pathways
(1) C4 Photosynthesis
Some plants (e.g., corn,sugarcane, and many
tropical grass) begin the photosynthetic process
by producing a four-carbon compounds. Plants of
this type are called C4 plants (e.g. live in hot
and dry environments and are able to
photosynthesize at low CO2 concentration)
(2) Crassulacean Acid Metabolism (CAM)

• Like C4 plant, CAM is an adaptation to hot dry
  environments
• CAM plats utilize both the C3 and the C4 pathways
  of photosynthesis
• CO2 is fixed by PEP (phosphhoenolpyruvate)
  carboxylase at night to
• form malic acid which is then is stored in the
  vacuole of the cell.

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Respiration Overview 1. Autotrophic
Respiration (Plant Respiration) A. Maintenance
Respiration B. Growth Respiration 2.
Heterotrophic Respiration (Soil Respiration)
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• 1.Autotrophic Respiration (Ra)

Ra involves the oxidation of organic substances
to CO2 and water CH2O O2 ---gt CO2 2H2O
energy
Total autotrophic respiration (Ra) consists of
two major components (1) Maintenance Respiration
(Rm) (2) Growth Respiration (Rs)

• Maintenance Respiration the basal rate of
  metabolism,
• includes the energy expended on ion uptake and
  transfer within plants.

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(a) The temperature is most important
environmental factor affecting maintenance
respiration Protein synthesis rates increase
exponentially with increasing temperature (T)
(b) The T dependence of Rm is expressed in term
of the Q10, or change in rate with a 10ºC rise
in temperature Rm (T) R0 Q10 (T-T0)/10
Where R0 is the basal respiration rate at T
0ºC (or ref. T) Q10 represents the change in the
rate of respiration for 10ºC change in T
(about 2.0-2.3)
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(c) using plant nitrogen content Micheal
Ryan (1991) derived an empirical relationship
based on a wide variety of species and plant
tissues   Rm 0.0106 N Where Rm is
maintenance respiration (moles C per hour), and N
is plant nitrogen in moles of N. (see Ryan
1991, Ecological Applications, 1 157-167).
Most of the organic N in plants is in protein and
about 60 Rm supports protein repair and
replacement
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(2) Growth Respiration (Construction respiration)
(a) Rg includes the carbon cost of synthesizing
new tissue from glucose and minerals. (b) Rg
for various tissues differ, depending on the
biochemical pathways involved.
(C) Growth respiration can be estimated based on
construction cost
e.g. 1 g lignin requires 2.5g of
glucose 1 g needles require 1.28 g of
glucose 1 g roots require 1.2 g of
glucose
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Estimating Growth respiration (Rg) Growth
respiration is generally considered to be
independent of temperature and is proportional
to GPP Where rg,i is a growth respiration
coefficient for plant component i, and ra,i is
the carbon allocation fraction for plant
component i. Ryan (1991) used 25 for overall
and root growth respiration coefficient. In
the TEM (Mellilo et al. 1993), 20 of GPP is
applied to growth respiration.  
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2. Heterotrophic Respiration (Rh)
1) Concept The form of respiration by which
organic matter is converted back into CO2,
mainly by soil micro-organisms.
Soil respiration (total soil CO2 flux)
including root respiration and decomposition
litter decomposition soil organic matter
decomposition
2) Modeling Rh

• Linear/nonlinear models
• Moisture and temperature combined models

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Linear/nonlinear model
Peng and Apps (2000) used the 150 sites published
by Raich and Schlesinger (1992) to develop TPAET
models for estimating soil respiration (SR) at
global scale
Group A Major Natural Ecosystems (n117) SR
7.6 exp (0.029T) P0.171 AET0.423
(R2 0.70)
Group B Croplands (n19) SR 0.66P 0.95 AET
7.11T 468 (R2 0.71)
Group C Wetlands (e.g. bogs, mires, and marshes)
(n14) SR 0.722 AET 0.023P-10.241T140
(R2 0.74)
Where T is mean annual temperature P is annual
precipitation AET is actual evapotranspiration
(Ref. Peng, C.H. and M.J. Apps 2000. J. of
Environmental Sciences, 12 257-265)
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Moisture and temperature combined models
In CENTURY (Parton et al, 1993), the rate of soil
C decomposition for each pool (Ri) is expressed
as Ri Ki Ci Md Td Where i
refers to different carbon pools,
Ci is the C stock for a particular pool,
Ki is the maximum decomposition rate,
and Md and Td are the
effects of soil moisture and temperature on
decomposition, which
are calculated as Md 1/ (1 4e
6Ws) Td 0.125 e 0.07Ts
where Ts is the soil temperature (ºC ) and Ws
is the soil water content ().
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Factors affecting respiration

• Tissue age
• Temperature
• Moisture (water stress)
• Atmospheric CO2
• Air pollution (ozone, sulphur dioxide)

Reading Reference Ryan, M. 1991. Effects of
climate change on plant respiration. Ecological
Application, 1(2) 157-167.