1. Presentation at NSERC Strategic Project Meeting – Guelph Jan 10, 2008 Claudia Wagner-Riddle Previous experience with isotopic CO 2 measurements of soil respiration Proposed research for 2008, 2009

2. Previous Project: Temporal Dynamics of Greenhouse Gas Fluxes linked to Soil Biophysical Processes and Management Practices Co-applicants: U. of Guelph, U. of Manitoba, AAFC Duration: Sep 30, 2004 to Sep 29, 2007 Funds for purchasing tunable diode laser trace gas analyzer for 13 CO 2 and 12 CO 2 concentration measurements One of objectives: –to determine fraction of soil CO 2 flux originating from soil organic carbon or crop residue carbon for no-tillage (NT) vs. conventional tillage (CT) over time

3. Research Site: Elora (Ontario) Four 1.5 ha plots: conventional practices (2 plots); "best management" practices (2 plots) since 2000; since May 2005 treatments these were NT and CT Corn/soybean/winter-wheat/corn/soybean over 2000 to 2004; corn in 2005

4. 2 (NT) 3 (NT) 1 (CT) 4 (CT) Trailer Four 1.5-ha Plots (Ontario)

5. Field: -air intakes (up/down x 4 plots) Trailer: -sampling manifold -tanks -dryer -TGA -pumps Stable Isotope Studies at Elora

7. 30 s tank A 30 s tank B 15 s each height for 4 min Switching cycle for one plot over 30 min

8. Weekly calibration (working vs. transfer or ’golden’ tanks)

9. Measured by TGA (diff. in conc. between 2 heights) Flux Ratio Calculation of  13 C R (Griffis et al., 2004) Note: Applicable to soil respiration only when vegetation is not present

10. CO 2 Fluxes Fall 2005 CT × NT +

11. Flux Ratio calculation of  13 C R Fall NT ~3.5‰ lower than CT plot Fall to Spring Change ~-4‰

12. Keeling Plots Footprint for concentration measurement larger than 1.5-ha plots so that difference between treatments can not be detected

13. Findings The respired soil CO 2 signature showed a stronger C4 signature compared to the no-till field where crop residue was left on the soil surface during fall and spring This means a larger proportion of measured soil CO 2 flux in fall originated from crop residue in CT compared to NT (76.2 vs. 61.5% in fall; 60% vs. 45.1% in spring) These results suggest that NT will increase C storage, contradicting previous studies in eastern Canada It may be that decomposition under NT increases at some time subsequent to the measurement periods reported here (i.e. summer, when vegetation is present)

14. New Research Question How to derive  13 C R from in-canopy 13 CO 2 and 12 CO 2 concentration measurements?

15. 13 CO 2 and 12 CO 2 concentrations measurements Proposed Meaurements Canopy measurements

16. Laser and Dewar PC ElectronicsAbsorption tubeReference cell and detector Sample cell and detector Edwards et al. (2002)

17. TGA100 adapted to measure mole fractions of 12 CO 2 and 13 CO 2 by Bowling et al. (2003) –Based on mostly same hardware –Software change to allow for simultaneous scanning of two absorption lines (one for each isotopomer) –Analyzer optimized for accuracy and precision TGA100 tested in 26-day field experiment in Minnesota (after soybean harvest) by Griffis et al. (2004) Characteristics: –10 Hz noise of  13 C 0.5‰, calibrated noise <0.15‰ –  13 C R can be obtained by ratio of fluxes (F 13 CO 2 /F 12 CO 2 ) instead of Keeling plot Stable Isotope Studies using TDLAS