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

Marcel van Oijen (CEH-Edinburgh)


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


Carbon fluxes in vegetation

P

R

Rg

Rm

Vegetation biomass


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


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


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


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


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


Carbon fluxes in vegetation


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)


Measurements of R & P in grassland

 = P

º = R

Wageningenrhizolab

(Ad Schapendonk)


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


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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