Soil Organic Carbon & Temperature Methodologies: strengths and weaknesses

1. Soil Organic Carbon & TemperatureMethodologies: strengths and weaknesses Christian Giardina Institute of Pacific Islands Forestry PSW Research Station USDA Forest Service Hilo, Hawaii 96720

2. Laboratory incubation. • short-term, long-term, substrate addition • 2. In situ 13C mass loss at sites with C3/C4 change across an MAT gradient. • 3. In situ 13C of soil surface CO2 efflux at sites with C3/C4 change across seasonal changes in temperature. • 4. Radiocarbon dating of soil C fractions coupled with modeling across gradients in MAT.

3. Canopy CO2 Litter Layer Roots Mineral soils Soil Carbon

4. Canopy CO2 Litter Layer Roots Mineral soils Soil Carbon

5. Canopy Laboratory Incubations Litter Layer Roots Mineral soils Soil Carbon

6. Incubation of 28 North American soils Fissore et al. 2009

8. Response of soils depleted in active C and fresh soils to changing temperature Fissore et al. In Review

9. Responses following glucose additions Fissore et al. In Review

10. Incubation approach Strengths Easy / inexpensive Permits comparisons across diverse soils Permits diverse manipulations

11. Incubation approach Weaknesses Highly altered conditions for decomposition temperature moisture inputs Disturbance of soils Everybody does it

12. Canopy In Situ 13C Analyses Litter Layer Roots Mineral soils t1 t0

13. Examine decomposition rate as function of MAT Giardina, Vucetich & Ryan In Prep.

14. In situ 13C mass loss approach Strengths Comparing in situ decomposition rates Large number of C3 / C4 field studies

15. In situ 13C mass loss approach Weaknesses Relies on disturbed sites Space (MAT) for time (Warming) substitution Potential for confounding cross-site effects

16. Canopy 13CO2 Litter Layer Roots Mineral soils t0 t1

17. In situ 13CO2 approach Strengths Comparing in situ decomposition rates

18. In situ 13CO2 approach Weaknesses Expensive / specialized equipment / few studies Relies on disturbed sites Potential for confounding seasonal effects Treats soil C as a single pool

19. Canopy Radiocarbon Analyses of SOC Fractions Litter Layer Roots Recalcitrant Slow Active

20. The MRT for active, slow and recalcitrant C in response to variation in MAT

21. In situ radiocarbon approach Strengths Comparing in situ decomposition rates Can be used in non-disturbed sites

22. In situ Radiocarbon approach Weaknesses Expensive / specialized equipment Space (MAT) for time (Warming) substitution Study comparisons are complicated by diverse methods and changing 14C in the atmosphere. “Ecosystem” residence times.

24. To address statistical uncertainty, we estimated the probability distribution of Q10 by combining WLS Regression with a 3-step bootstrap approach (α,k, and regression coefficients) to calculate 1000 bootstrap estimates of Q10 (Rawlings et al. 1998). Probability Q10>1.0 (0.50) Q10>1.2 (0.20) Q10>1.3 (0.10)