(daily) net photosynthesis (PSN) and (annual) net primary production (NPP)
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Transcript of (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
day
fAPARIPARAPAR
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APARPSN
APARNPP
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
NDVIfAPAR so for fixed
day
IPARPSN
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)(day
IPARNDVINPP
incident solar radiation (IPAR) also from RS(Dubayah, 1992)
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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 :
mggross YYf
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mggross YYf
- conversion efficiency of grossphotosyn. (= 2.7 gC/MJ)
f - fraction of daytime when photosyn. notlimited (base tempt. etc)
Yg - fraction of photosyn. NOT used bygrowth respiration (65-75%) Ym - fraction of photosyn. NOT used bymaintainance respiration (60-75%)
gross
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define max - max. efficiency
max gross g mY Y
so
f maxmax - determined by plant form f - determined by climate
base / max temperature water or other stresses - light availability
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estimate max - land cover LUT for biome characteristics
estimate f - climatological inputs can link to index of temperature/moisturestress from surf. temp / VI
also require global Met. data (IPAR, rainfall)
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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, 9:747-766.
• Monteith, J.L., (1977). Climate and efficiency of crop production in Britain. Phil. Trans. Royal Soc. London, B 281:277-294.
• Running, S.W., Nemani, R., Glassy, J.M. (1996) MOD17 PSN/NPP Algorithm Theoretical Basis Document, NASA.