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 Xu, Baldocchi, Tang, 2004 Global Biogeochem Cycles

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

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]

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

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 CO 2 Time Series – McNaughton and Spriggs, BLM

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

Rain pulses in the lab In a factorial experiment, we induced an artificial precipitation pulse on 36 intact soil cores at 4 sampling dates in summer 2010 Measured CO 2 efflux for 36 hours following the pulse using an LI-820 Soil/No Litter Soil/Shaded Litter Soil/ Photodegraded Litter Low Precip (0.5mL)n=6 High Precip (2mL)n=6

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litter High precip: No litter Shaded litter Photodegraded litter Lab precipitation pulse, 25 June 2010 Hatala et al, unpublished

Rain pulses in the lab ANOVA  Results: 1.Both the precipitation levels and litter treatments have a significant effect on efflux (p<0.001) 2.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.

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

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

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

Regional Change in Atmospheric CO 2 following Rain-Induced Respiration Pulses

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

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

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

Coupled PBL-Sfc Energy CO 2 Model: al a McNaughton-Spriggs

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

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

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

Test of Webb Pearman Leuning Density Corrections over an Aeroport Tarmac