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

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

Kuyzakov 2006 Partitioning Soil Respiration: Principles

Measure Soil Temperature at the Location of the Source

Girdling Experiment Hogberg et al. 2000, Nature

Experimental Treatments Under a Tree: ~R a +R h Open Grassland: ~R h (summer)

Tonzi Ranch/Oak Savanna

Vaisala GMT 220

Continuous Soil Respiration with soil CO 2 Sensors [CO 2 ] must be corrected for temperature

Theory/Equations Moldrup et al F cp : fraction silt and sand;  : constant;  porosity;  : air-filled pore space

Validation with Chambers Baldocchi et al. JGR Biogeoscience, 2006

Validation with EC Baldocchi et al. JGR Biogeoscience, 2006

Results and Discussion

CO 2 in the Soil: Between and Under a Tree

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

Effects of temperature, soil moisture, rain and photosynthesis on CO 2 Efflux Baldocchi et al. JGR Biogeoscience, 2006

When Does Root Respiration Initiate?: Prior, Coincident or After the Start of Photosynthesis Canopy Ps starts ~d80R auto starts ~d100

Temperature: hysteresis and lags Tang et al GCB 2005

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

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

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

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

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