on the relative magnitudes of photosynthesis, respiration, growth and carbon storage in vegetation
DESCRIPTION
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 ) - PowerPoint PPT PresentationTRANSCRIPT
On the relative magnitudes of
photosynthesis, respiration, growth and carbon storage
in vegetationMarcel van Oijen (CEH-Edinburgh)
Carbon fluxes in vegetation
PRm Rg
R
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
PRm Rg
R
Vegetation biomass
Carbon fluxes in vegetation
PRm Rg
R
Reserves StructureG
NPP = P – Rg – Rm
= G + SRg = G (1-Yg) / Yg
G (1-¾) / ¾= G / 3
S = P-Rm-Rg-G
ρ = (Rg + Rm) / Pα = S / P
Rm / P =Rg / P =G / P =S / P =
Carbon fluxes in vegetation
PRm Rg
R
Reserves StructureG
NPP = P – Rg – Rm
= G + SRg = G (1-Yg) / Yg
G (1-¾) / ¾= G / 3
S = P-Rm-Rg-G
ρ = (Rg + Rm) / Pα = S / P
Rm / P = (4ρ+α-1) / 3Rg / P = (1-ρ-α) / 3G / P = 1-ρ-αS / P = α
Knowing two parameters, ρ and α,fully determines P : Rg : Rm : S : G
Carbon fluxes in vegetation
Rm / P = (4ρ+α-1) / 3Rg / P = (1-ρ-α) / 3G / P = 1-ρ-αS / P = α
ρ = 1/2
α = 1/4
Vertical bar represents
P = Rm + Rg + G + S
Carbon fluxes in vegetation
Rm / P = (4ρ+α-1) / 3Rg / P = (1-ρ-α) / 3G / P = 1-ρ-αS / P = α
Rm = 5/12
Rg = 1/12
G = 1/4
S = 1/4
ρ = 1/2
α = 1/4
Carbon fluxes in vegetation
Rm / P = (4ρ+α-1) / 3Rg / P = (1-ρ-α) / 3G / P = 1-ρ-αS / P = α
0
1
3/43/16 1
RgRm
S
G
α = 1/4
ρ Excluded becauseρ < (1-α)
Excluded becauseρ > (1-α)/4
Carbon fluxes in vegetation
0
1
1/8 1/21/4 1
G
RmRg G
S
RmRg
α = 0 α = 1/2
ρ
0 10
1
3/43/16 1
RgRm
S
G
α = 1/41
Carbon fluxes in vegetation
Rm / P = (4ρ+α-1) / 3Rg / P = (1-ρ-α) / 3G / P = 1-ρ-αS / P = α
ρ < (1-α)
ρ > (1-α)/4
Constraints on the respiration ratio ρ
Constraints on the storage ratio α
(1-4ρ) < α < (1-ρ)
Measurements of R & P in grassland
0
25
50
75
0 50 100 150 200 250 300 350Time (d)
Respiration (R, g CO2 m-2 d-1)Photosynthesis (P, g CO2 m-2 d-1) = P
º = R
Wageningen rhizolab(Ad Schapendonk)
Measurements of R & P in grassland
0
25
50
75
0 50 100 150 200 250 300 350Time (d)
Respiration (R, g CO2 m-2 d-1)Photosynthesis (P, g CO2 m-2 d-1) = P
º = R
-1
0
1
2
0 50 100 150 200 250 300 350
Time (d)
R:P (=ρ)S:P (=α)
`
º = R/P=ρ = S/P=α
Rg = Rm Net remobilisation of reserves: 3-11 d after each cut
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 α must 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