daily net photosynthesis PSN and annual net primary production NPP

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(daily) net photosynthesis (PSN)and(annual) net
primary production (NPP)
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PSN and NPP

• (daily) net photosynthesis (PSN)
• (annual) net primary production (NPP)
• relate to net carbon uptake
• important for understanding global carbon budget
  (climate change)

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PSN and NPP

• C02 removed from atmosphere
• photosynthesis
• C02 released by plant (and animal)
• respiration
• Net Photosynthesis (PSN)
• net carbon exchange over 1 day (photosynthesis -
  respiration)

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PSN and NPP

• Net Primary Productivity (NPP)
• annual net carbon exchange
• quantifies actual plant growth
• (not just C02 fixation)

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Algorithms - require to be model-based

• simple Production efficiency model (PEM)
• (Monteith, 1972 1977)
• relate PSN, NPP to APAR
• APAR from PAR and fAPAR

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• PSN daily total photosynthesis
• NPP, PSN typically accum. of dry matter (convert
  to C by assuming DM 48 C)
• efficiency of conversion of PAR to DM
  (g/MJ)
• equations hold for non-stressed conditions

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to characterise vegetation need to
know

• Efficiency
• fAPAR

so for fixed
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Determining

• herbaceous vegetation (grasses)
• av. 1.0-1.8 gC/MJ for C3 plants
• higher for C4
• woody vegetation
• 0.2 - 1.5 gC/MJ
• simple model for

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NPP, gC/m2 - from 30 (desert) to gt 1000 (tropical
rainforest.
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• References
• Dubayah, R. (1992) Estimating net solar radiation
  using Landsat Thematic
  Mapper and Digital Elevation data. Water
  resources Res., 28 2469-2484.
• Monteith, J.L., (1972) Solar radiation and
  productivity in tropical
  ecosystems. J. Appl. Ecol, 9747-766.
• Monteith, J.L., (1977). Climate and efficiency of
  crop production in
  Britain. Phil. Trans. Royal Soc. London,
  B 281277-294.
• Running, S.W., Nemani, R., Glassy, J.M. (1996)
  MOD17 PSN/NPP Algorithm Theoretical Basis
  Document, NASA.
• http//www.forestry.umt.edu/ntsg/RemoteSensing/net
  primary/