1 / 22

The diffusive movement of CO 2 into and out of a leaf can be described by Fick’s Law:

At the same time, H 2 O vapor moves out of the leaf by diffusion (but really H2O vapor moves both directions). CO 2 moves from the air to the leaf to the chloroplast by diffusion (but really CO2 moves both directions). Net flux of “x” = F x.

lindsay
Download Presentation

The diffusive movement of CO 2 into and out of a leaf can be described by Fick’s Law:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. At the same time, H2O vapor moves out of the leaf by diffusion (but really H2O vapor moves both directions) CO2 moves from the air to the leaf to the chloroplast by diffusion (but really CO2 moves both directions)

  2. Net flux of “x” = Fx (a membrane or barrier with a “conductance” to substance “x” = gx) The diffusive movement of CO2 into and out of a leaf can be described by Fick’s Law: Net flux = D concentration * conductance [xo] = concentration of “x” on the “outside” of “barrier” [xi] = concentration of “x” on the “inside” of the “barrier” Fx = ([xo] – [xi]) * gx

  3. Applying Fick’s Law to carbon assimilation : Net C assimilation = (ca-ci) * gleaf Or: Aleaf = ca(1- ci/ca) * gleaf (Norman 1982; Franks & Farquhar 1999)

  4. Modeling Canopy Photosynthesis(GPP) αmax (CO2) GPP (Mg ha-1) (soil moisture) (D, temperature) Absorbed PAR (MJ ha-1)

  5. How can we describe the response of α to changes in the environment? α = A / PAR α is light-use efficiency; units: g C / Joule light energy A is for C assimilation (or photosynthesis, GPP of a leaf); units: g C / m2 leaf area PAR is light on the leaf surface (think APAR); unit: Joule light energy / m2 leaf area We know a lot about the response of A to changes in the Environment!!! A = gs * (Ca – Ci) This is Fick’s diffusion equation describing that the flux (here of CO2) is proportion to the conductance (here leaf conductance through the stomata) and the difference in concentration (here of CO2 between the inside and outside of the leaf)

  6. How can we describe the response of α to changes in the environment? We begin withα = A / PAR And know that A = gs * (Ca – Ci) Which can be re-written A = gs * Ca * (1 – Ci / Ca) Now we can ask: What do we know about the responses ofgs, Ca, and Ci / Ca to changes in the environment?? As a simple example, we begin withCa.

  7. Begin with setting the ratio of response AE = gsE * CaE * (1 – Ci / Ca)E AA = gsA * CaA * (1 – Ci / Ca)A R = • Two examples of the RELATIVE change in A (and therefore α): • only Ca changes • changes in Ca affects gs and Ci / Ca • only Ca changes – increases by 50% • R = 1 * 1.5 * 1 = 1.5; •  α increases by a factor 1.5 (2) Ca increases 50%; plants respond by decreasing gsby 10% and increasing Ci / Ca (from 0.7) by 5% R = 0.9 * 1.5 * ((1 – 0.735) / (1 – 0.70)) = 0.9 * 1.5 * 0.88 = 1.19  α increases by a factor ~1.2

  8. Modeling Canopy Photosynthesis(GPP) αmax (CO2) GPP (Mg ha-1) (soil moisture) (D, temperature) Absorbed PAR (MJ ha-1)

  9. Factors affecting net assimilation (A) and stomatal conductance (gleaf): • Vapor pressure deficit, D (that is related to the humidity of the air) • Soil Moisture,  • Temperature, T Aleaf = ca (1- ci/ca) * gleaf f(D,  ) f(T)

  10. Factors affecting net assimilation (A) and stomatal conductance (gleaf): • Vapor pressure deficit, D (that is related to the humidity of the air) • Soil Moisture,  • Temperature, T Aleaf = ca (1- ci/ca) * gleaf f(D,  ) f(T)

  11. Relative conductance gleaf/gleaf-maximum Stomata (canopy) conductance D (kPa) D (kPa) Stomata respond to the vapor pressure deficit between leaf and air (D). Stomata generally close as D increases and the response is often depicted as a nonlinear decline in gs with increasing D. (Breda et al. 2006) (Oren et al. 1999)

  12. 1 Relative conductance gleaf/gleaf-maximum 0 5 2 3 4 1 Vapor pressure deficit, D (kPa) 1 gleaf/gleaf-maximum= 1 0.6 Relative conductance gleaf/gleaf-maximum gleaf/gleaf-maximum= -0.6 LnD +1 0 0 LnD (Vapor pressure deficit) (Oren et al. 1999)

  13. GPP =  {f(D)f(T)f() f(CO2)}*APAR  = Aleaf/PAR Aleaf= ca (1- ci/ca) * gleaf Stomata respond to the vapor pressure deficit between leaf and air (D). Stomata generally close as D increases and the response is often depicted as a nonlinear decline in gs with increasing D. If D <1, then gleaf/gleaf-max = 1  Aleaf/Aleaf-max = 1   / max = 1 If D > 1, then gleaf/gleaf-max= -0.6 LnD +1  Aleaf/Aleaf-max < 1   / max < 1

  14. Stomata respond to changes in soil moisture ( ). During water shortage, when drops below ca. 0.2, gleaf declines gradually down to very low values 0.1 0.2 0.3 0.4 Soil moisture, (m3 m-3) Modified after Breda et al. (2006)

  15. 1 0.2 Relative conductance gleaf/gleaf-maximum 0.08 0 0.5 0.2 0.3 0.4 0.1 Soil moisture, (m3 m-3) gleaf/gleaf-maximum = 1 1 gleaf/gleaf-maximum = s +b Relative conductance gleaf/gleaf-maximum s 0 0.5 0.2 0.3 0.4 0.1 Soil moisture, (m3 m-3)

  16. GPP =  {f(D)f(T)f(CO2)f()}*APAR  = Aleaf/PAR Aleaf= ca (1- ci/ca) * gleaf Stomata respond to changes in soil moisture ( ). During water shortage, when drops below ca. 0.2, gleaf declines gradually down to very low values If  > 0.2, then gleaf/gleaf-max = ? Aleaf/Aleaf-max = ?   / max = ? If  < 0.2, then gleaf/gleaf-max= ? Aleaf/Aleaf-max < ?   / max < ?

  17. Factors affecting net assimilation (A) and stomatal conductance (gleaf): • Vapor pressure deficit, D (that is related to the humidity of the air) • Soil Moisture,  • Temperature, T Aleaf = ca (1- ci/ca) * gleaf f(D,  ) f(T)

  18. Temperature effect on Ci/Ca and on net assimilation Ci: Typical CO2 concentration is about 270-300 ppm Ca= external CO2 concentration (Ca = 380-400 ppm?)

  19. 0.6 Ci/Ca 0 20 30 40 5 Temperature (C) 1 A/Amax 0 20 30 40 5 Temperature (C)

  20. GPP =  {f(D)f(T)f(CO2)f()}*APAR  = Aleaf/PAR Aleaf= ca (1- ci/ca) * gleaf ci/carespond to changes in temperature (T). Under low or high T, ci/caincreases gradually to high values If T <20C or T> 30C, then ci/ca = ? Aleaf/Aleaf-max = ?   / max = ? If 20 C<T <30C, then ci/ca = ? Aleaf/Aleaf-max = ?   / max = ?

  21. Next week’s assignment: 1) Using clumping indexes, LAI and  values for a conifer stand (Loblolly pine forest, Duke Univ.) and for a Eucalyptus plantation (New Zealand), calculate their Monthly GPP(potential GPP). - Loblolly pine: = 0.05 molC molAPAR-1 (2.74 gC MJ-1 APAR ) - Eucalyptus plantation:  = 0.07 molC molAPAR-1 (3.85 gC MJ-1 APAR) 2) Assuming that all of the above parameters vary by plus or minus 20%, calculate how Annual GPP would be affected for each forest type. , Clumping =constant , Clumping =constant GPP GPP +20% -20% +20% LAI -20% LAI , LAI =constant , LAI =constant Loblolly pine GPP GPP Eucalyptus +20% -20% +20% Clumping -20% Clumping Clumping, LAI =constant Clumping, LAI =constant GPP GPP +20%  -20% +20%  -20%

  22. References Breda N. et al. 2006. Temperate forest trees and stands under severe drought: a review. Annals of Forest Science. 63:625-644. Dye, P.J. et al. 2004. Verification of 3-PG growth and water-use predictions in twelve Eucalyptus plantation stands in Zululand, South Africa. For. Ecol. Management. 193:197–218 FranksPJ, FarquharGD. 1999. A relationship between humidity response, growth form and photosynthetic operating point in C3 plants. Plant, Cell Environment 22:1337–1349. Norman J. M. 1982. Simulation of microclimates, in Biometeorology in integrated pest management, edited by J. L. Hatfield and I. J. Thomason, p. 65-99, Academic, New York. Oren R. et al. 1999. Survey and synthesis of intra- and interspecific variation in stomatal sensitivity to vapour pressure deficit. Plant, Cell and Environment 22: 1515-1526 Waring W.H. and S.W. Running 1998. Forest ecosystem analysis at multiple scales. 2nd Ed. Academic press. San Diego, CA 370p.

More Related