1. Breathing of the Terrestrial Biosphere: How Physics Sets the Limits, Biology Does the Work Dennis Baldocchi Department of Environmental Science, Policy and Management University of California, Berkeley Kuehnast Lecture University of Minnesota, Oct 2009

2. Outline Why Study Trace Gas and Energy Fluxes? How We Study Fluxes? What Lessons have we Learned? – Leaf – Canopy – Continental/Globe

3. Why Study Trace Gas and Energy Fluxes? Changes in Concentration in the Atmosphere are due to Trace Gas Fluxes into and out of the Atmosphere Trace Gas and Energy Fluxes define the Lower Boundary Condition for Weather, Climate, Hydrological, Atmospheric Chemistry and Biogeochemical Cycling Models Fluxes are being Used to Validate and Parameterize Models and Remote Sensing Algorithms that Integrate Fluxes in Time and Space Allow Us to Discover New Emergent Processes at Ecosystem Scale

4. Change in C (mass, population, moles) per unit volume with TIME (t) equals the Difference between the Fluxes (F, C per unit area per unit time) In and Out of the given Volume Fluxes vs Concentrations: Solving the Bathtub Problem

5. What the Biosphere Breathes? ESPM 2, The Biosphere

6. Overarching Themes Relating to the Study of Biosphere-Atmosphere Trace Gas Exchange Many Connected Processes and Feedbacks Non-linearity/complexity/chaos are Ubiquitous – Beware of UnIntended Consequences Systems operate across a Spectrum of Scales Systematic Scaling Rules Emerge, at times New Processes Emerge, at other times

7. Biogeophysical-Ecohydrological View

8. Controlling Processes and Linkages: Roles of Time and Space Scales

9. ESPM 2 The Biosphere The Baldocchi-Biometeorology Perspective Physics ‘wins’, or sets the Limits – Plants and Ecosystems function by capturing solar energy – Plants convert solar energy into high energy carbon compounds for work growth and maintenance respiration – There is only ‘so-much’ solar energy available to a given area of land This limits the number and size of plants, eg many small or few big plants per unit area – Plants transfer nutrients and water between air, soil and plant pools to sustain their structure and function, via diffusion and mass transfer. Biology is how it’s done – Species differentiation (via evolution and competition) produces the structure and function of plants, invertebrates and vertebrates – In turn, structure and function provides the mechanisms for competing for and capturing light energy and transferring matter, – And reproductive success that passes genes through the gene pool. – Microbes break down and recycle biological material – Microbes exploit electron gradients in biomass and their environment

10. BioPhysical Rules/Constraints on Ecosystems Ecosystem Photosynthesis scales with Intercepted Sunlight Intercepted Sunlight scales with Leaf Area Index Leaf Area Index scales with  (Photosynthesis –Respiration) Photosynthesis > Respiration Transpiration is the Cost of Photosynthesis Evaporation < Rainfall – If not: – Stomatal Closure Must Occur – and/or:  (Photosynthesis –Respiration) is Reduced – and/or: Leaf Area is Reduced – and/or: Light Interception and Photosynthesis is Reduced ESPM 2 The Biosphere

11. Scientific Approach

12. ESPM 2, The Biosphere Eddy Covariance Fluxes Net Flux is the sum of the mass flux moving across a plane (w C) in the up and down-drafts

13. Study Sites Crops: soybeans, alfalfa, wheat, corn, rice Deciduous Forest Savanna Woodland Boreal Conifer Forest Grassland and peatland pastures

14. FLUXNET: From Sea to Shining Sea 500+ Sites, circa 2009 www.fluxdata.org ESPM 2, The Biosphere

15. Acquire Metadata on Leaf, Soil and Ecosystems Structure and Function, too Assess Leaf Photosynthetic Capacity and Stomatal Control Partition Ecosystem Fluxes according to Soil and Vegetation Components Acquire Information on Canopy Structure with Active (LIDAR) and Passive Remote Sensing

16. Canopy Modeling, e.g. CANVEG: A Tool to Integrate, Distill and Interpret Fluxes

17. Basics of Ecosystem-Atmosphere Interactions

18. Leaf Structure, Function & Physiology

19. ESPM 129 Biometeorology Source-Sink Term, S, equals the Flux Divergence, dF/dz a(z), Leaf area density (m 2 m -3 ) r a, boundary layer resistance (s m -1 ) – f(wind velocity, leaf size) r s, stomatal resistance (s m -1 ) – f(CO 2, light, soil moisture, plant function) C(z), scalar mole density (mole m -3 ) – f(wind and turbulence, Source-Sink, S(z) Ci, internal molar density (mole m -3 ) – f(physiological capacity)

20. ESPM 2 The Biosphere Relations between leaf nitrogen, mass-based photosynthesis, specific leaf weight and lifespan: A  w/ N A ↓ w/ age N ↓ w/ age N  :thickness ↓ Highest mass-based Photosynthesis is with short living, thin leaves with high N Lowest mass-based photosynthesis is with old thick leaves with low N

21. Leaf Mass, Photosynthesis and N per unit Area Vary with Canopy Height ESPM 2 The Biosphere Here, Thick Leaves have More N and Greater Photosynthesis

22. ESPM 111 Ecosystem Ecology Wilson et al., 2001 Tree Physiol [N] Thickness [N] After Reich et al 1997, PNAS Its all about Light!

23. High V cmax must be Achieved in Seasonally- Droughted Ecosystems to attain Positive Carbon Balance Area under the Curves are Similar

24. To Achieve High Ps Capacity, Blue Oak Leaves must be Even Thicker and Retain N

25. Isotopes Infer Leaf Temperatures of Tree Leaves are Constrained, ~ 21 C Helliker and Richter 2008 Nature Leaf Temperature Growing Season Temperature

26. Leaf Temperature, Modeled with CANOAK, as a Central Tendency near 20 C Canoak Model

27. Isotopes Evaluate a Flux-Weighted Temperature

28. Canopy Scale How does Evaporation and Net Carbon Exchange vary with Climate and Ecosystem? How can we Mitigate Global Warming by Varying Attributes of Canopies, and their associate Energy and Mass Fluxes?

29. Biometeorological View to Evaporation Penman Monteith Equation Function of: Available Energy (Rn-S) Vapor Pressure Deficit (D) Aerodynamic Conductance (Gh) Surface Conductance (Gs)

30. Crop Evaporation is Strongly Coupled to Radiation Boardman, OR; 1991

31. But Corn (C 4 ) Doesn’t Evaporate like Wheat (C 3 )! Boardman, OR; 1991

32. Plus Forests Do not Evaporate Like Crops

33. Effects of Functional Types and R sfc on Normalized Evaporation R c is a f(LAI, N, soil moisture, Ps Pathway) Priestley-Taylor  = 1.26

34. You Need Water to Grow Trees, Maintain high LAI and Achieve a Low Surface Resistance!

35. ESPM 129 Biometeorology Highest Normalized Evaporation Comes with High LAI and Vcmax( leaf N) Priestley-Taylor  = 1.26

36. Eco-hydrology: ET, Functional Type, Physiological Capacity and Drought

37. Use Appropriate and Root-Weighted Soil Moisture to Assess Normalized Evaporation Rates Soil Moisture, arthimetic average Chen et al, 2008 WRR Soil Moisture, root-weighted

38. What types of landscapes are better or worse sinks for Carbon? How does Carbon Assimilation and Respiration respond to Environmental stresses, like drought, heatspells, pollution? Are Forests Effective Mitigators for stalling Global Warming?

39. Carbon Uptake of Crops is a Linear Function of Sunlight: An Emergent Property of the EcoSystem

40. ESPM 129 Biometeorology Canopy Light Response Curves: Effect of Diffuse Light

41. Knohl and Baldocchi, 2008 JGR Biogeosciences Explaining the Diffuse Light Effect

42. Remote Sensing of Canopy Structure and GPP

43. Remote Sensing and Ecosystem Metabolism

44. ESPM 111 Ecosystem Ecology Ryu, Ma, Falk, Sonnentag, Baldocchi, submitted Frontiers of Ecology Refining Spectral Vegetation Indices for Remote Sensing of Fluxes from Space

45. What Happens to the Grass?; It is too Dry to Promote Microbial Decomposition June October

46. PhotoDegradation Can Be a Important Pathway for Carbon Loss in Semi-Arid Rangelands (~20-30 gC m -2 season -1 )

47. Sustained and Elevated Respiration after Fall Rain

48. Why Do Rain pulses Produce more C from Open Grassland than Understory? Xu et al. 2003 GBC

49. Continental and Global Scale

50. Baldocchi, Austral J Botany, 2008 Ecosystem Respiration (F R ) Scales Tightly with Ecosystem Photosynthesis (F A ), But Is with Offset by Disturbance

51. FLUXNET 2007 Database GPP at 2% efficiency and 365 day Growing Season Potential and Real Rates of Gross Carbon Uptake by Vegetation: Most Locations Never Reach Upper Potential tropics GPP at 2% efficiency and 182.5 day Growing Season

52. ESPM 111 Ecosystem Ecology What is the Upper Bound of GPP? Bottom-Up: Counting Productivity on leaves, plant by plant, species by species Top-Down: Energy Transfer

53. ESPM 111 Ecosystem Ecology Upper-Bound on Global Gross Primary Productivity Global GPP is ~ 120 * 10 15 gC y -1 Solar Constant, S* (1366 W m -2 ) – Ave across disk of Earth S*/4 Transmission 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 (4.6/10 6 ) – Mean photosynthetic photon flux density, Q p Fraction of absorbed Q p (1-0.1=0.9) Photosynthetic efficiency, a (0.02) Arable Land area (~ 110 * 10 12 m 2 ) 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*110 10 12 *43200*180*12/(4* 10 6 )=120* 10 15 gC y -1

54. Global distribution of Flux Towers Covers Climate Space Well Can we Integrate Fluxes across Climate Space, Rather than Cartesian Space?

55. Global GPP = 1033 * 110 10 12 m 2 = 113.6 PgC/y Probability Distribution of Published GPP Measurements, Integrated Annually

56. Spatial Variations in C Fluxes Xiao et al. 2008, AgForMet spring summer autumn winter

57. Baldocchi, Austral J Botany, 2008 Net Ecosystem Carbon Exchange Scales with Length of Growing Season

58. Length of Growing Season, in Temperate Ecosystems, is associated with the timing between soil temperature and mean annual air temperature

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

60. Baldocchi, White, Schwartz, unpublished Spatialize Phenology with Transformation Using Climate Map

61. E. Falge et al 2002 AgForMet; Baldocchi et al 2001 BAMS Optimal NEE: Acclimation with Temperature

62. If Papal Indulgences can save us from burning in Hell: Can Carbon Indulgences save us from Global Warming? Sixtus IV Alexander VI Innocent VIII Julius II Leo X

63. Working Hypotheses H1: Forests have a Negative Feedback on Global Warming – Forests are effective and long-term Carbon Sinks – Landuse change (more forests) can help offset greenhouse gas emissions and mitigate global warming H2: Forests have a Positive Feedback on Global Warming – Forests are optically dark and Absorb more Energy – Forests have a relatively large Bowen ratio (H/LE) and convect more sensible heat into the atmosphere – Landuse change (more forests) can help promote global warming

64. Case Study: Energetics of a Grassland and Oak Savanna Measurements and Model

65. Case Study: Savanna Woodland adjacent to Grassland 1.Savanna absorbs much more Radiation (3.18 GJ m -2 y -1 ) than the Grassland (2.28 GJ m -2 y -1 ) ;  Rn: 28.4 W m -2

66. Landscape Differences On Short Time Scales, Grass ET > Forest ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

67. Role of Land Use on ET: On Annual Time Scale, Forest ET > Grass ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

68. 4a. U* of tall, rough Savanna > short, smooth Grassland 4b. Savanna injects more Sensible Heat into the atmosphere because it has more Available Energy and it is Aerodynamically Rougher

69. 5. Mean Potential Temperature differences are relatively small (0.84 C; grass: 290.72 vs savanna: 291.56 K); despite large differences in Energy Fluxes--albeit the Darker vegetation is Warmer Compare to Greenhouse Sensitivity ~2-4 K/(4 W m -2 )

70. Conceptual Diagram of PBL Interactions H and LE: Analytical/Quadratic version of Penman-Monteith Equation

71. The Energetics of afforestation/deforestation is complicated Forests have a low albedo, are darker and absorb more energy But, Ironically the darker forest maybe cooler (T sfc ) than a bright grassland due to evaporative cooling

72. But Warmer Air Temperatures Occur after considering PBL, Longwave Energy loss, R a and albedo….!! Summer Conditions

73. Physical Limits on Oak Savanna, and Biological Solutions

75. Mass Exchange of C, H 2 O, N and P Stomata on Leaves must open for CO 2 to Enter – CO 2 is the prime substrate for the energy compound glucose Water diffuses out of the Leaf – Roots must take up soil water and transfer it to the leaf through the phoelem to keep cells turgid The assimilation of CO 2 relies on a reaction catalyzed by the enzyme RUBISCO – RUBISCO contains many Nitrogen molecules per mole Energy from Sunlight is converted to the energy compound ATP – Phosphorous must be assimilated ESPM 2 The Biosphere

76. Stomatal Conductance Scales with Photosynthesis Wilson et al. 2001, Tree Physiology Schulze et al 1994. Annual Rev Ecology Photosynthetic Capacity Scales with Nitrogen and Ps Pathway Stomatal Conductance scales with Nitrogen Stomatal Conductance Scales with N, via Photosynthesis

77. PhotoDegradation is not an Artifact of Temperature Data of Baldocchi and Ma, processed by S. Rutledge et al.

78. Forests Transpire effectively, causing evaporative cooling, which in humid regions may form clouds and reduce planetary albedo

79. Theoretical Difference in Air Temperature: Grass vs Savanna Summer Conditions

80. Temperature Difference Only Considering Albedo Spring Conditions

81. Stand Age also affects differences between ET of forest vs grassland