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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:  = 2.37 gC MJ -1 APAR - PowerPoint PPT Presentation

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  • Next weeks 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: = 2.37 gC MJ-1 APAR - Eucalyptus plantation: = 3.85 gC MJ-1 APAR2) Assuming that all of the above parameters vary by plus or minus 20%, calculate how Annual GPP would be affected for each forest type.GPP-20%+20%LAI, Clumping =constantGPP-20%+20%Clumping, LAI =constantGPP-20%+20%Clumping, LAI =constantGPP-20%+20%LAI, Clumping =constantGPP-20%+20%Clumping, LAI =constantGPP-20%+20%Clumping, LAI =constantLoblolly pineEucalyptus

  • 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: = 2.37 gC MJ-1 APAR ; - Eucalyptus plantation: = 3.85 gC MJ-1 APAR

  • Actual GPPs

    Pine = 2500 gC m-2 year-1Euca = 3300 gC m-2 year-1

    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.

  • GPP = {f(D)f(T)f() f(CO2)}*APARProductivity equationConstraints to photosynthesis = Aleaf / PARMaximum potential photosynthesis rateCanopy quantum efficiencyAleaf = ca (1- ci/ca) * gleafLight supply and light capture

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

  • (note that this leaf has stomata only on the abaxial or bottom side. Some leaves also have stomata on the adaxial, or upper surface. Leaves with stomata on both sides are called amphistomatous)Some definitions .

  • CO2 diffuses into leaves, moving down a concentration gradientCa = 370-400 ppm?Typical CO2 concentration of a C3 plant at midday is about 270-300 ppmThe CO2 concentration at the site of fixation approaches zero

  • The diffusive movement of CO2 into and out of a leaf can be described by Ficks Law:

    Net flux = D concentration * conductance[xo] = concentration of x on the outside of barrier[xi] = concentration of x on the inside of the barrierFx = ([xo] [xi]) * gx

  • Conductance is a PROPERTY of leaf, kind of analogous to its porosity to CO2 or H2O vapor. It is NOT a rate!!! Conductance is the inverse of resistance. Both quantities are commonly used. The symbol g is commonly used for conductance, r for resistancegH2O = conductance to water vaporgCO2 = conductance to CO2gs = stomatal conductance (usually to water vapor)gl = total leaf conductance (usually to water vapor) The units used for conductance and resistance can be very confusing -

  • Applying Ficks Law to carbon assimilation :Net C assimilation = (ca-ci) * gleaf

    Or: Aleaf = ca (1- ci/ca) * gleaf(Norman 1982; Franks & Farquhar 1999)

  • 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)

  • 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)

  • Humidity and vapor pressure deficitThe portion of total air pressurethat is due to water vapor is

    water vapor pressure (ea)

    measured in kPa

  • When air has no extra capacityfor holding water, the vapor pressureis termed:saturation vapor pressure (es, units kPa)

    Saturation vapor pressure is mostly a function of air temperatureWhen air temperature falls withouta change in water content, thepoint of condensation is called thedew point temperature

  • Relative Humidityis the ratio between actual vapor pressure (ea)and saturation vapor pressure (es)RH = ea/esVapor Pressure Deficit (D)is the difference between saturation vapor pressure (es)and actual vapor pressure (ea)D = es - ea

  • 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)

  • LnD (Vapor pressure deficit)Vapor pressure deficit, D (kPa)0101Relative conductancegleaf/gleaf-maximum105324Relative conductancegleaf/gleaf-maximumgleaf/gleaf-maximum= -0.6 LnD +10.6gleaf/gleaf-maximum= 1(Oren et al. 1999)

  • 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= -0.6 LnD +1 Aleaf/Aleaf-max < 1 / max < 1

    GPP = {f(D)f(T)f() f(CO2)}*APAR = Aleaf/PARAleaf = ca (1- ci/ca) * gleaf

  • Stomata respond to changes in soil moisture ( ). During watershortage, when drops below ca. 0.2, gleaf declines graduallydown to very low valuesSoil moisture, (m3 m-3)0.10.30.20.4Modified after Breda et al. (2006)

  • Soil moisture, (m3 m-3)010.10.50.30.20.4gleaf/gleaf-maximum = s +bRelative conductancegleaf/gleaf-maximumgleaf/gleaf-maximum = 1s010.10.50.30.20.40.20.08Soil moisture, (m3 m-3)Relative conductancegleaf/gleaf-maximum

  • If > 0.2, then gleaf/gleaf-max = ? Aleaf/Aleaf-max = ? / max = ?

    If < 0.2, then gleaf/gleaf-max= ? Aleaf/Aleaf-max < ? / max < ?

    GPP = {f(D)f(T)f(CO2)f()}*APAR = Aleaf/PARAleaf = 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

  • 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)

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

  • Temperature (C)0A/AmaxCi/Ca5302040Temperature (C)00.653020401Warren and Dreyer (2006)

  • If T 30 C, then ci/ca = ? Aleaf/Aleaf-max = ? / max = ?

    If 20 C

  • Final assignment:Just calculate GPP and have fun experimenting !GPP = {f(D)f(T)f() f(CO2)}*APAR

  • 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. 193:197218

    Franks PJ, Farquhar GD. 1999. A relationship between humidity response, growth form and photosynthetic operating point in C3 plants. Plant, Cell Environment 22:13371349.

    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.

    Warren C.R. and E. Dreyer. 2006. Temperature response of photosynthesis and internal conductance to CO2: results from two independent approaches. Journal of Experimental Botany 57:3057-3067.