Slide 1

Using Biophysical Models and Eddy Covariance Measurements to Ask (and Answer) Questions About Biosphere-Atmosphere InteractionsDennis Baldocchi

Biometeorology LabESPMUniversity of California, Berkeley

1Conservation of Mass, e.g. Solving the Bathtub Problem

The Level in a Tub depends on the Fluxes IN and OUT of the TubWhat is the State of the Atmosphere?

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IsotopicexchangeCourtesy of Jose Fuentes, UVaTrace Gas and Energy Fluxes between Land and the Atmosphere3maybe add isotope fluxes here (see orange)

Quantifying Sources and SinksBiology: Leaf area density, a(z) internal conc, Cistomatal resistance, rsPhysics: Boundary layer resistance, rbScalar conc, C(z)4Biogeophysical-Ecohydrological View

5Controlling Processes and Linkages:Roles of Time and Space Scales

6Sub-Grid Variability:What Errors arise from Averaging?

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Eddy Covariance Technique

Oak SavannaAnnual GrasslandPeatland/PastureTemperate Deciduous ForestBoreal Conifer ForestCrops8FLUXNET: From Sea to Shining Sea400+ Sites, circa 2007

9PhysiologyPhotosynthesisStomatal ConductanceTranspirationMicrometeorologyLeaf/Soil Energy BalanceRadiative TransferLagrangian Turbulent Transfer

CANVeg MODEL10Key Attributes of CanVegSeasonalityLeaf Area IndexPhotosynthetic Capacity (Vcmax)Model parameters based on Site Measurements and EcoPhysiological Rules and Scaling FunctionsStomatal Conductance scales with PhotosynthesisJmax and Rd scale with VcmaxMultilayer FrameworkComputes Fluxes (non-linear functions) on the basis of a leafs local environmentConsidersSun and Shade Leaf FractionLeaf ClumpingLeaf Inclination AngleNon-local Turbulent Transport and Counter-Gradient Transfer

11ESPM 228, Advanced Topics in Micromet and Biomet

Models Must Consider Seasonality in Leaf Area Index and Photosynthetic Capacity, VcmaxWilson et al. 2001 Tree Physiol

12Results and Discussion

13ESPM 111 Ecosystem Ecology

Can Principles from a Global Network Produce Insights about Global-Scale Fluxes?

What is the Upper Bound of GPP and its Variability?Bottom-Up:Counting Productivity on leaves, plant by plant, species by speciesTop-Down:GPP Scales with Energy

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FLUXNET 2007 DatabaseGPP at 2% efficiency and 365 day Growing SeasonPotential and Real Rates of Gross Carbon Uptake by Vegetation:Most Locations Never Reach Upper PotentialtropicsGPP at 2% efficiency and 182.5 day Growing Season15ESPM 111 Ecosystem EcologyUpper-Bound on Global Gross Primary ProductivityGlobal GPP is ~ 120 * 1015 gC y-1

Solar Constant, S* (1366 W m-2)Ave across disk of Earth S*/4Transmission of sunlight through the atmosphere (1-0.17=0.83)Conversion of shortwave to visible sunlight (0.5)Conversion of visible light from energy to photon flux density in moles of quanta (4.6/106)Mean photosynthetic photon flux density, QpFraction of absorbed Qp (1-0.1=0.9)Photosynthetic efficiency, a (0.02)Arable Land area (~ 100 * 1012 m2)Length of daylight (12 hours * 60 minutes * 60 seconds = 43200 s/day)Length of growing season (180 days)Gram of carbon per mole (12)

GPP = 1366*0.83*0.5*4.6*0.9*0.02*100*1012*43200*180*12/4=108*1015 gC y-116

Random Sampling Error Reaches Equilibrium with > 60 Sites17Interannual Variability in GPP is small, and not significantly different, across the Global Network

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Little Change in Abiotic Drivers--annual Rg, ppt --across Network

19Answering Questions with ModelsRoles of Structure and FunctionLeaf Angles and ClumpingLeaf Area IndexPhotosynthetic CapacityPhenologyRoles of Microclimate Conditions on Mass and Energy ExchangeDiffuse LightHumidityTemperatureSub-Grid Parameterization, Energy Balance Closure and ScalingInsights from a 2-D, Wet DaisyWorld20

CO2 Flux Model Test: Hourly to Annual Time Scales21Stress need to use ensembles of flux data, not instantaneous data points, they have errors too, both sampling and biasTime Scales of Interannual Variability

Baldocchi et al., 2001 Ecological Modeling22ESPM 111 Ecosystem Ecology

Role of Proper Model Abstraction

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How Long should one Measure Fluxes?:Decadal Power Spectrum of CO2 and Water Vapor Fluxes24Emergent Processes: Impact of Leaf Clumping on Canopy Light Response Curves

25Interaction between Clumping and Leaf Area

26ESPM 228 Adv Topics Micromet & Biomet

clumpedrandomsphericalerectophileplanophileNEE (gC m-2 a-1)-577-354-720-1126-224lE (MJ m-2 a-1)16901551177420231473H (MJ m-2 a-1)10961032109511711008How Sensitive are Fluxes to Leaf Inclination Angle Distribution?

27ESPM 228 Adv Topics Micromet & Biomet

Vcmax(73)Vcmax(50)% differenceNEE (gC m-2 a-1)-577-454-21.3lE (MJ m-2 a-1)16901584-6.3H (MJ m-2 a-1)109611999.3Carbon, Water and Sensible Heat Exchange scale with Photosynthetic Capacity28ESPM 228 Adv Topics Micromet & Biomet

0.1 m0.01m0.001 mNEE (gC m-2 a-1)-577-588-586lE (MJ m-2 a-1)169016521615H (MJ m-2 a-1)109611641202Leaf Size has a Modest Effect on Carbon & Water Exchange, But a Large Effect on Sensible Heat Exchange29

Are VOCs a Large Source of Carbon?30Isoprene is about >1.1% of canopy photosynthesis on annual basis

Net Ecosystem Carbon Exchange scales with Growing Season LengthBaldocchi et al, 2001 Ecological Modeling31

Baldocchi et al., 2005 Int J Biomet.Soil Temperature: An Objective Indicator of Phenology??32Baldocchi et al. Int J. Biomet, 2005Soil Temperature: An Objective Measure of Phenology, part 2

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Baldocchi, White, Schwartz, unpublishedSpatialize Phenology with Transformation Using Climate Map

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White, Baldocchi and Schwartz, unpublishedFlux Based Phenology Patterns with Match well with data from Phenology Network35

How do Sky Conditions Affect Net Carbon Exchange (NEE)?: DataBaldocchi, 1997 PCE

Niyogi et al., GRL 200436

More Diffuse than Direct Light is Intercepted37

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Knohl and Baldocchi, 2008 JGR BiogeosciThe Diffuse-Light Enhancement is a function of LAI39

Knohl and Baldocchi, 2008 JGR BiogeosciThere are Trade-Offs between Reducing Light Amount (with Clouds and Aerosol) and Increasing Light Use Efficiency40Canopy Photosynthesis and Aerosols:Impact on Daily & Annual Time Scales, II

referencedirect radiation, -20%% differenceNEE (gC m-2 a-1)-577-65513.5lE (MJ m-2 a-1)169017292.3H (MJ m-2 a-1)10961058-3.541

Simple Model suggests A/T decreases with increasing D or Ci/Ca

42Water Use Efficiency: Ci/Ca , Vapor Pressure Deficit and Diffuse Light Fraction

But Complex feedbacks among Ci/Ca, humidity and diffuse light need to be considered!

Knohl and Baldocchi, unpublished43Note simple scheme suggesnt A/E increases as ci/ca decreases, but they hold D const.How Do Changes in vpd and Ci/Ca conspire to affect A/T?

44would it be interesting to look at diffuse/total instead of ci/ca and then in the next slide on A/T vs. ci/ca. I suggest not to use a and b as parameters in the second equations since it looks very much like = a + (b-a) Ci/Ca

In toto (considering coupled energy balance feedbacks) A/T increases with Ci/Ca

45A/T, Stable Isotope Discrimination and Diffuse Light

Knohl and Baldocchi, unpublished

46I found the equation with deltaa-deltap less clear than a verbal description. Is Delta canopy flux weighted? I guess that high discrimination values mainly occur in the morning and evening hours. Values for delta are very high!ESPM 111 Ecosystem EcologyLeaf Size and ExtinctionMajor Extinction at Triassic-Jurassic Boundary during period of Elevated Greenhouse effect4 fold increase in CO23 to 4 C temperature increase99% species turnover of megaflora with leaves > 5 cm10% species turnover of flora with leaves < 0.5 cmSmall Leaves are more effective in transferring heat and experiencing lethal surface temperaturesMcElwain et al Science, 199947

Why are Leaves Certain Sizes?Biophysics as an Evolutionary FilterLeaf Temperature and Leaf Morphology

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Leaf size, CO2 and Temperature: Why are oak leaves small in CA and large in TN?49

Leaf Temperature and Isotopes?

Helliker and Richter 2008 Nature

Flat line is for angiosperms50

Sub-Grid Variability:Lessons Derived from Wet DaisyWorldLatent Heat Exchange Map51what is the unit?

Baldocchi et al, 2005 Tellus

Spatial Variation in subGrid T and LE follows Power Law Scaling52Sub-Grid Scaling Errors in ET

53ConclusionsBiophysical Model aids in understanding the impact of diffuse light on photosynthesis, isoprene emission, water use efficiency and stable isotope discrimination

A cellular automata, energy balance model shows that spatial averaging of energy balance drivers can produce huge errors in grid-scale energy fluxes and can explain lack of energy balance closure54AcknowledgementsFunding NASA, DOE/TCP, NIGEC/WESTGEC, NSF, MicrosoftEddy Covariance MeasurementsKell Wilson, Bev Law, Alexander KnohlFLUXNETEva Falge, Lianhong Gu, Deb Agarwal et alCanopy Modeling and Diffuse LightAlexander Knohl, Lianhong Gu, Kell WilsonIsoprenePeter Harley, Jose Fuentes, Dave Bowling, Russ Monson & Alex Guenther13C IsotopesAlexander Knohl, Dave Bowling, Russ Monson55