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On the relative magnitudes of photosynthesis, respiration, growth and carbon storage in vegetation

On the relative magnitudes of photosynthesis, respiration, growth and carbon storage in vegetation. Marcel van Oijen (CEH-Edinburgh ). Carbon fluxes in vegetation. P. R. R g. R m. ρ = R/P is often ~0.5 Gifford (1995): ρ  f(Temp.) Cheng et al. (2000): ρ  f(CO 2 )

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On the relative magnitudes of photosynthesis, respiration, growth and carbon storage in vegetation

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  1. On the relative magnitudes ofphotosynthesis, respiration, growth and carbon storagein vegetation Marcel van Oijen (CEH-Edinburgh)

  2. Carbon fluxes in vegetation P R Rg Rm • ρ = R/P is often ~0.5 • Gifford (1995):ρ f(Temp.) • Cheng et al. (2000): ρ f(CO2) • Physiological explanation ? • Monteith (1981) • Mathematical explanation ! • Law of conservation of mass … Vegetation biomass

  3. Carbon fluxes in vegetation P R Rg Rm Vegetation biomass

  4. Carbon fluxes in vegetation NPP = P – Rg – Rm = G + S Rg = G (1-Yg) / Yg  G (1-¾) / ¾ = G / 3 P R Rg Rm ρ = (Rg + Rm) / P α= S / P Structure Reserves Rm / P= Rg / P = G / P = S / P = G S = P-Rm-Rg-G

  5. Carbon fluxes in vegetation NPP = P – Rg – Rm = G + S Rg = G (1-Yg) / Yg  G (1-¾) / ¾ = G / 3 P R Rg Rm ρ = (Rg + Rm) / P α= S / P Structure Reserves Rm / P = (4ρ+α-1) / 3 Rg / P = (1-ρ-α) / 3 G / P = 1-ρ-α S / P = α G S = P-Rm-Rg-G Knowing two parameters, ρ and α, fully determinesP : Rg : Rm : S : G

  6. Carbon fluxes in vegetation α = 1/4 Vertical bar represents P = Rm + Rg + G + S Rm / P = (4ρ+α-1) / 3 Rg / P = (1-ρ-α) / 3 G / P = 1-ρ-α S / P = α ρ = 1/2

  7. Carbon fluxes in vegetation α = 1/4 Rm = 5/12 Rg = 1/12 G = 1/4 Rm / P = (4ρ+α-1) / 3 Rg / P = (1-ρ-α) / 3 G / P = 1-ρ-α S / P = α S = 1/4 ρ = 1/2

  8. Carbon fluxes in vegetation α = 1/4 1 R m R Excluded because ρ> (1-α)/4 g G Rm / P = (4ρ+α-1) / 3 Rg / P = (1-ρ-α) / 3 G / P = 1-ρ-α S / P = α S 3/16 3/4 1 0 Excluded because ρ< (1-α) ρ

  9. Carbon fluxes in vegetation

  10. Carbon fluxes in vegetation Constraints on the respiration ratio ρ ρ> (1-α)/4 Constraints on the storage ratio α (1-4ρ) < α< (1-ρ) Rm / P = (4ρ+α-1) / 3 Rg / P = (1-ρ-α) / 3 G / P = 1-ρ-α S / P = α ρ< (1-α)

  11. Measurements of R & P in grassland  = P º = R Wageningenrhizolab (Ad Schapendonk)

  12. Measurements of R & P in grassland  = P º = R Rg = Rm Net remobilisation of reserves: 3-11 d after each cut º = R/P=ρ  = S/P=α

  13. Discussion • Conservation of mass strongly constrains C-fluxes • Eqs are valid over any period & any spatial scale (with P>0) • Eqs are valid for any environmental conditions  little impact of temperature and CO2 • In periods of net remobilisation (α<0), eqs still valid but then ρ can be >1 • Long-term value of αmust be >0 (otherwise reserves depleted)  fluxes most constrained over longer periods (Monteith, 1981) • Steady-state growth would require α = constant (~0.2?) to maintain homeostasis • Eqs tool for: • Analysis of incomplete data sets • Checking internal consistency of models

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