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