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Pulses in Ecosystem Respiration Induced by Rain—Scaling From Soil to Canopy to Region. Dennis Baldocchi, Siyan Ma, Jaclyn Hatala, and Beniamino Gioli University of California, Berkeley IBIMET-Firenze, Italia. Motivation, P1: More C emanates from the Sunny Grassland than the Shaded Understory.

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Pulses in Ecosystem Respiration Induced by Rain—Scaling From Soil to Canopy to Region


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    1. Pulses in Ecosystem Respiration Induced by Rain—Scaling From Soil to Canopy to Region Dennis Baldocchi, Siyan Ma, Jaclyn Hatala, and Beniamino Gioli University of California, Berkeley IBIMET-Firenze, Italia

    2. Motivation, P1:More C emanates from the Sunny Grassland than the Shaded Understory Xu, Baldocchi, Tang, 2004 Global Biogeochem Cycles

    3. Motivation, p2 • Summer C effluxes from bone dry grasslands were greater than expected • Yet, Grasses Disappear over the course of the Summer after Cows have been Removed

    4. Hypotheses • Photodegradation Pre-Conditions Litter so Pulses are greater from Sunnier Sites • The Most Labile Carbon is lost First, by Opportunistic Microbes Adapted to Dry-Wet Pules • First seasonal pulse exceeds latter pulses, irregards of rain amount • Pulsing Effects Occur across Broad Regions of Semi-Arid Grasslands and Enhances Regional [CO2]

    5. Objectives • Mechanisms: • Invoke Rain Pulses at the Soil Core/Plot scale • Spatial Scaling to the Field • Role of Pulses at the Field Scale on Carbon Balance • Impact: • Change in [CO2]in the Planetary Boundary Layer

    6. Methods • Replicated Plots/Lab Cuvette Flux Measurements • Litter Samples Exposed to Sun and Shade and Subject to ‘Rain’ • Eddy Covariance Flux Measurements • Annual Grassland, Oak Savanna Understory, Peatland Pasture • PBL Box Model and CO2 Time Series • McNaughton and Spriggs, 1986..BLM

    7. Field Sites in N. California • Grassland, Vaira Ranch, Ione, CA • Oak Woodland Understory, Tonzi Ranch, Ione, CA • Peatland Pasture, Sherman Island, Antioch, CA

    8. In a factorial experiment, we induced an artificial precipitation pulse on 36 intact soil cores at 4 sampling dates in summer 2010 • Measured CO2 efflux for 36 hours following the pulse using an LI-820 Rain pulses in the lab

    9. Lab precipitation pulse, 25 June 2010 • Low precip: • No litter • Shaded litter • Photodegraded litter • High precip: • No litter • Shaded litter • Photodegraded litter Rain pulses in the lab CO2 efflux (umol m-2 s-1) Hatala et al, unpublished time (hours) Respiration peaks rapidly after a precipitation pulse, and decreases more slowly.

    10. ANOVA  Results: • Both the precipitation levels and litter treatments have a significant effect on efflux (p<0.001) • There is a significant positive interaction (p=0.024) between precipitation and litter treatment, where both of the litter treatments have higher efflux than the control. Rain pulses in the lab

    11. Synthesis of 55 events over 21 SiteYears of Pulses at 3 sites Ma et al. Global Change Biology, in Review

    12. The total amount of CO2 emission emanating from an Average Reco pulse was 31.5, 26.6, and 94.6 gC m-2 at the open grassland, the woodland understory and the peatland pasture, respectively.

    13. Greatest Pulses, 1st and at Sunniest Sites • Type I pulse is the first pulse occurring right after summer drought; • Type II pulse is the sequencing pulse. Ma et al. Global Change Biology, in Review

    14. Ma et al. Global Change Biology, in Review

    15. Regional Change in Atmospheric CO2following Rain-Induced Respiration Pulses

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

    17. 1D modelling results (lines) against observations (circles) daily time scale

    18. Conclusions.. • C pulses account for 10% of annual C budget of Grasslands • C Pulses are regular and repeated feature of C balance in many semi-arid Ecosystems • New Generation of Ecosystem Respiration Models must consider rain induced respiration pulses • The pulse are a function of antecedent conditions (number of previous pulses, amount of solar radiation) • Rain-Induced Respiration Pulses have Regional implications that elevate [CO2] through Enhancing Evaporation, which produces a shallower PBL, and by Enhancing the C source Flux

    19. Coupled PBL-Sfc Energy CO2 Model:al a McNaughton-Spriggs

    20. NOAA HYSPLIT 24 hours back trajectories, ending at Tonzi-Vaira Period: Oct 14-25, 2009 (post rain event of Oct 13) EDAS meteorological data Day of October, 2009 • air mostly coming from N-W, northern central valley • first 2 days from S-E central valley • 1 day from ocean

    21. Tonzi-Vaira daily average fluxes for 2009 blu window is the modelling study period (next graphs)

    22. Eddy Flux Evidence of Photodegratation Enhancing CO2 Efflux Moffett Field Test of Zero Flux Rutledge et al. 2010 Global Change Biology Fc (wind dir 0|60) = 0.375 +/- 0.129 (se)

    23. Test of Webb Pearman Leuning Density Corrections over an Aeroport Tarmac Fc (wind dir 0|60) = 0.375 +/- 0.129 (se)