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Dennis Baldocchi, Jianwu Tang & Liukang Xu

Separation of ‘Autotrophic’ and ‘Heterotrophic’ Respiration in an Oak-Grass Savanna and their Link with Canopy Photosynthesis. Dennis Baldocchi, Jianwu Tang & Liukang Xu. Biometeorology Lab Dept Environmental Science, Policy and Mgt University of California, Berkeley.

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Dennis Baldocchi, Jianwu Tang & Liukang Xu

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  1. Separation of ‘Autotrophic’ and ‘Heterotrophic’ Respiration in an Oak-Grass Savanna and their Link with Canopy Photosynthesis Dennis Baldocchi, Jianwu Tang & Liukang Xu Biometeorology Lab Dept Environmental Science, Policy and Mgt University of California, Berkeley CarboEurope, Crete, 2006

  2. Outline • Introduction • Quantifying Roles of Lags, Pulses and Switches • Objectives • Methods • Site Description • Continuous Soil CO2 Measurements • Flux-gradient measurements • Results and Discussion • Responses to temperature, rain pulses and photosynthetic activity • Test with Eddy Covariance

  3. Partitioning Soil Respiration: Principles Kuyzakov 2006

  4. Measure Soil Temperature at the Location of the Source

  5. Girdling Experiment Hogberg et al. 2000, Nature

  6. Experimental Treatments Under a Tree: ~Ra+Rh Open Grassland: ~Rh (summer)

  7. Tonzi Ranch/Oak Savanna

  8. Vaisala GMT 220

  9. Continuous Soil Respiration with soil CO2 Sensors [CO2] must be corrected for temperature

  10. Theory/Equations Moldrup et al. 1999 Fcp: fraction silt and sand; b: constant; f:porosity; e: air-filled pore space

  11. Validation with Chambers Baldocchi et al. JGR Biogeoscience, 2006

  12. Validation with EC Baldocchi et al. JGR Biogeoscience, 2006

  13. Results and Discussion

  14. CO2 in the Soil:Between and Under a Tree

  15. What Happens After Rain? • Microbial Stimulation • It occurs for 4 days, until the soil dries • Evacuation of Pores • cannot be sustained for several days

  16. Effects of temperature, soil moisture, rain and photosynthesis on CO2 Efflux Baldocchi et al. JGR Biogeoscience, 2006

  17. When Does Root Respiration Initiate?: Prior, Coincident or After the Start of Photosynthesis Canopy Ps starts ~d80 Rauto starts ~d100

  18. Temperature:hysteresis and lags Tang et al GCB 2005

  19. Why?:Respiration Lags Photosynthesis, v1:Hourly Scale Tang et al GCB 2005

  20. Continuous Measurements Enable Use of Inverse Fourier Transforms to Quantify Lag Times Tang et al GCB 2005

  21. Respiration Lags Photosynthesis, v2:Daily Scale Tang et al GCB 2005

  22. Conclusions • Profile systems with soil CO2 sensors can be used to measure soil respiration with confidence • Natural gradients can be used to separate effects of autotrophic and heterotrophic respiration • Recent photosynthate is translocated to the soil and stimulates soil respiration • This causes a decoupling between soil respiration and soil temperature • Soil respiration under active trees is much greater than under dead grass

  23. Biometeorology Team Liukang Xu Jianwu Tang Ted Hehn Funding: US DOE/TCP; WESTGEC/NIGEC; Kearney Soil Science Found.,Ca Ag Expt Station, AmeriFlux

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