University of California, Berkeley Using Biophysical Models to Ask (and Answer) Questions About Biosphere-Atmosphere Interactions Dennis Baldocchi Alexander Knohl James Dorsey Biometeorology Lab University of California, Berkeley ILEAP Meeting Boulder, CO Jan, 2006

ILEAPS Paradigm Isotopic exchange maybe add isotope fluxes here (see orange)

Sub-Grid Variability: What are Errors in ET Scaling?

Answering Questions with Models Diffuse Radiation Light Use Efficiency Isoprene emission Water Use Efficiency Stable Isotopes Sub-Grid Parameterization, Energy Balance Closure and Scaling Insights from a 2-D, ‘Wet’ DaisyWorld

CANVeg MODEL Physiology Photosynthesis Stomatal Conductance Transpiration Micrometeorology Leaf/Soil Energy Balance Radiative Transfer Lagrangian Turbulent Transfer

Key Attributes of CanVeg Seasonality Leaf Area Index Photosynthetic Capacity (Vcmax) Model parameters based on Site Measurements and EcoPhysiological Rules and Scaling Stomatal Conductance scales with Photosynthesis Jmax and Rd scale with Vcmax Multilayer Framework Computes Fluxes (non-linear functions) on the basis of a leaf’s local environment Considers Sun and Shade Leaf Fraction Leaf Clumping Leaf Inclination Angle Non-local Turbulent Transport and Counter-Gradient Transfer

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

Another Form of Model Testing: Reproducing Spectral Fidelity Note tested independently by other groups, katul @duke, Simon MPI-Mainz, Knohl MPI Jena, Fuentes Virginia Baldocchi et al, 2001 Ecological Modeling

Results and Discussion

How Sky Conditions Affect Net Carbon Exchange (NEE)?: Data Baldocchi, 1997 PCE

CO2 Flux and Diffuse Radiation: Data from AmeriFlux Niyogi et al., GRL 2004

Volcanoes, Aerosols + NEE

How do Changes in Diffuse Radiation affect Canopy Fluxes?: Case: Mt Pinatubo Explosion, ~ 10% of beam -> diffuse direct beam Solar radiation [W m-2] Year of Mt. Pinatubo eruption legend and labels are very small, I changed it a bit diffuse Solar elevation angle [°] Gu et al, 2003, Science

Canopy Photosynthesis and Aerosols: Impact on Daily & Annual Scales, I increase diffuse by 10% beam: 1527 gC m-2 y-1 + 51 gC m-2 y-1, the operator += might not be familiar to everybody, maybe better to write “increase diffuse by 10% of beam:” The overall effect is not very large 50 gC = 3% Canopy Photosynthesis may increase by +50 gC m-2 y-1

Conventional Wisdom: More Light Absorption with Diffuse Radiation WHY? Conventional Wisdom: More Light Absorption with Diffuse Radiation

More Efficient Use of Light by Shade Leaves? is PPFD only beam? Maybe two figures one with PPFD only beam and one with 0.5 diffuse/total

vpd is Correlated with Diffuse Fraction: Less Physiological Stress (?) Stomatal conductance vs vpd or direct diffuse

Isoprene is about >1.1% of canopy photosynthesis on annual basis

Isoprene and Diffuse Radiation 0.8% increase, note greatest changes happened on the sunniest and warmest days, indicating a weak but more coupled sensitivity to temperature rather than light

Stable Isotope Discrimination and Diffuse Light Preference of photosynthesis for light 12CO2 vs. heavier 13CO2 I 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!

Autocorrelations among Ci/Ca, vpd and diffuse/Total

Water Use Efficiency (A/T) and diffuse light

Simple Model suggests A/T decreases with D or Ci/Ca e.g. A/T of C4 > C3 But Complex feedbacks need to be considered!

How Do Changes in vpd and Ci/Ca conspire to affect A/T? would 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

Sub-Grid Variability: Lessons Derived from Wet DaisyWorld Latent Heat Exchange Map what is the unit?

Eddy covariance footprints and ecosystem representativeness Footprint representation Newly developed 3d Lagrangian stochastic footprint model was run for a 1 m canopy and 3 m measurement height. Half a million trajectories were integrated to calculate the source probability density. The footprint calculation was run using the same grid geometry as the DaisyWorld simulation to allow convolution of the results. The EC “tower” was placed in different locations in the simulated ecosystem, and the EC system's view of the ecosystem was calculated.

Eddy covariance footprints and ecosystem representativeness Each histogram shows 500 separate tower locations within the simulated ecosystem.

Errors in ET Scaling

Conclusions Biophysical 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 closure

Acknowledgements Funding Diffuse Light and Carbon Isoprene NASA, DOE/TCP, NIGEC/WESTGEC Diffuse Light and Carbon Lianhong Gu Isoprene Peter Harley, Jose Fuentes, Dave Bowling, Russ Monson & Alex Guenther 13C Isotopes Dave Bowling, Russ Monson Footprints & DaisyWorld Monique Leclerc, Tess Krebs, Joon Kim, Peter Levy, HaPe Schmid, Brian Amiro

Canopy Photosynthesis and Aerosols: Impact on Daily & Annual Time Scales, II

Role of Diffuse Light on Water Use Efficiency: A/E

Baldocchi et al, 2005 Tellus

Quantifying Sources and Sinks Biology: Leaf area density, a(z) internal conc, Ci stomatal resistance, rs Physics: Boundary layer resistance, rb Scalar conc, C(z)

Partial Explanation: Fiso is very sensitive to Leaf Temperature, which changed little in response to the imposed direct to diffuse partitioning