Climate controls over NPP

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Climate controls over NPP

• At a global scale, NPP is strongly correlated
  with ppt and T
• Water increases plant growth in drier ecosystems.
  Also increases decomposition and nutrient
  cycling.
• In very wet ecosystems, ppt can limit NPP by
  decreasing light or nutrient availability

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Climate controls over NPP

• Temperature is related to growing season length
• Temperature stimulates decomposition and nutrient
  cycling.

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Climate controls over NPP
In ecosystems where correlations suggest a strong
climatic limitation of NPP, experiments and
observations indicate that this is mediated
primarily by climatic effects on belowground
resources.
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Resource control

• Proximate control over NPP is availability of
  resouces
• Light, CO2, H2O, nutrients (N,P,K,Mg,Ca,)

• Many ecosystems increase NPP when N or P
  fertilizer is added.
• Some ecosystems increase NPP when CO2 or H2O is
  added.
• Where T has been manipulated, NPP doesnt respond
  directly.

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Vitousek and Farrington 1997
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Variation in NPP
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Global Potential Net Primary Productivity
Mg C ha -1 yr-1
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Biome Differences in NPP (Terrestrial)

• Length of the growing season is the major factor
  that explains biome differences in NPP

• Differences in leaf area account for most of the
  variation in biome NPP within a growing season

• Leaf area, in turn, is determined by soil
  resources, climate, and time since disturbance

• Disturbance substantially modifies the
  relationship between NPP and climate

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NEP is the balance between two large fluxes GPP
and ecosystem respiration
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Ecosystem Carbon Balance
Net Ecosystem Production (NEP)
GPP - Recosys
Net Ecosystem Exchange (NEE) is fairly similar,
but
Remember to check the sign convention!
Sensu Chapin et al. 2006
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Is NEE accumulation of C in the ecosystem, or
in the atmosphere?
Valentini et al. 1998
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Ecosystem Carbon Balance
Net Ecosystem Carbon Balance (NECB)
Net rate of C accumulation or loss
dC/dt
Sensu Chapin et al. 2006
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Ecosystem Carbon Balance
Net Ecosystem Carbon Balance (NECB) GPP -
Recosys ? other C transfers
Recosys Resp. of plants, animals, and soil
microbes

• NECB NPP ? Flateral
• Rheterotrophic
• -Fdisturb
• -Fleach
• -Femiss

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Ecosystem Carbon Balance
Ecosystem
0 -
NEP
(a very long) time
Atmosphere
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Ecosystem Carbon Balance

• Positive NECB GPP gt Recosys other C losses
• ecosystem is removing C from the atmosphere C
  sink
• Negative NECB GPP lt Recosys other C losses
• ecosystem is releasing C to the atmosphere C
  source

• Factors that affect GPP and C losses
  differentially will change NECB

• Increased CO2 and N deposition have greater
  direct effect on GPP. Reduction in soil moisture
  in a wetland may have a greater effect on
  Rheterotroph and fire

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GPP is invariant across latitudes
As a result, NEE decreases with latitude
While Re decreases as latitude (T proxy) increases
Valentini et al. 1998
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• Lecture ended here

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Eddy Covariance (NEE)
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Eddy Covariance Network
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Net Ecosystem Exchange
Tower network observations show that most
ecosystems that have been measured are net sinks
for CO2
1. Ecosystems may be typically net sinks of C in
between disturbance (no steady state)
2. Recent environmental changes such as increased
atm. CO2 or N deposition may be stimulating GPP
more than Recosystem
3. C loss through leaching and other transfers
may be an important component of regional C
balance
4. Mid-successional ecosystems with high NPP may
be over represented in the network
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Ecosystem Carbon Balance
Ecosystem
Atmosphere
Net Biome Production (NBP) NECB, integrated
over large spatial scales to include removal of C
by fire and harvest
Sensu Schultze et al. 1997
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