1. The age of C respired from ecosystems Susan Trumbore, Jim Randerson, Claudia Czimczik, Nicole Nowinski (UC Irvine) Jeff Chambers (Tulane) Eric Davidson (Woods Hole Research Center) Ted Schuur (Univ. Florida) Simone Vieira, Plínio Camargo (Centro de Energía Nuclear na Agricultura, USP, Brazil)

2. The age of C respired from ecosystems Photosynthesis leaf stem root Allocation storage Microbial community Stabilized SOM Soil respiration Litter and SOM decomposition Ecosystem respiration Root Respiration Fire Loss by leaching, erosion

3. Why this might be interesting Measure of the capacity for storage of C and interannual variability in C balance Isodisequilibrium; improve 13 C deconvolutions Potential for direct comparison of data with models Time C stored C lost C stored Deviation from mean

4. Radiocarbon of soil-respired CO 2 provides a direct measure of isodisequilibrium “mean age” of several years up to a decade  14 C Atmosphere- north hemisphere from Levin and Hessheimer 2000

5. Local atmosphere (Autotrophic respiration) CASA Empirical Soil respired CO 2 is a mix of heterotrophic and autotrophic sources Data from Harvard Forest, MA Heterotrophic values – from models

6. Heterotrophic Respiration can be measured by putting litter and 0-5 cm soil cores in sealed jars, then measuring the rate of CO 2 evolution and the isotopic signature of evolved CO 2.

7. Local atmosphere (Autotrophic respiration) Soil respired CO 2 is a mix of heterotrophic and autotrophic sources O horizon A horizon CO 2 evolved in incubation Data from Harvard Forest, MA Flux weighted mean

8.  14 C =  14 C of CO 2 evolved in incubation -  14 C of CO 2 in atmosphere Latitude of site Tropical forest Desert shrub Temperate forest Boreal forest Manaus, Santarem Joshua Tree* Harvard, Bear Brook 3 age stands Manitoba* *see posters by Czimczik, Nowinski

9. Flux-weighted total heterotrophic respiration for comparison with model Tropical forest Desert shrub Temperate forest Boreal forest Manaus, Santarem Joshua Tree* Harvard, Bear Brook 3 age stands Manitoba* Latitude

10. Determine age of respired CO 2 using pulse-response function for CASA Years since pulse CO 2 respired Tropical forest Desert shrub Temperate forest Boreal forest Thompson,and Randerson, Global ChangeBiol., 1999.

11. Age of respired C (yr) Fraction of total respiration Tropical forest Desert shrub Temperate forest Boreal forest Mean age of heterotrophically respired C from CASA range from 10- 40 years

12. Tropical forest Desert shrub Temp. forest Boreal forest Fraction of total respiration  14 C X 14 C from CASA X

13. Model-data comparison initially disappointing at low latitudes CASA Prediction 20 years ~ 4 years Latitude

14. Agreement improves if the oldest 25-50% of respired CO 2 is removed 100% 75% 50% 25% Latitude

15. Problems with incubations Overemphasis of ‘young’ part of the respiration distribution –Exclusion of woody debris from soil sampling will bias against the longer ‘tail’ - Artifacts with incubation in general - Inclusion of roots in incubations emphasizes ‘young’ pools (variation with time)

16. Potential issues with CASA Too long of a ‘tail’ - treats wood as a single pool with homogeneous turnover (do we need multiple pools to reflect different life strategies in tropical forest? Vieira et al. in revision PNAS) - model may allocate too much NPP to stem growth in tropical forests (stem allocation <1/3 of NPP)

17. 2.0 dead wood (50-100) yr Total heterotrophic respiration ~10 (11-24 yr) Total autotrophic respiration ~20 (0.01-1 yr) Total ecosystem respiration ~30 (3 – 8 yr) 3.3 leaf litter (2-3 yr) 4.7 Root/SOM (5-10 yr) Photosynthesis (~30) Rootrespiration Fluxes from Chambers et al. Units are MgC ha -1 yr -1 Dead wood excludes trees <10cm DBH Observations Manaus ZF2

18. 0 dead wood (50-100) yr Total heterotrophic respiration ~10 (4-7 yr) Total autotrophic respiration ~20 (0.01-1 yr) Total ecosystem respiration ~30 (0.9-1.6 yr) 3.3 leaf litter (2-3 yr) 6.7 Root/SOM +wood (5-10 yr) Photosynthesis (~30) Rootrespiration Fluxes from Chambers et al. Units are MgC ha -1 yr -1 Dead wood excludes trees <10cm DBH Bias removes wood component

19. 3.3 dead wood (50-100) yr Total heterotrophic respiration ~10 (20-37 yr) Total autotrophic respiration ~20 (0.1-1 yr) Total ecosystem respiration ~30 (7-24 yr) 3.3 leaf litter (2-3 yr) 3.3 Root/SOM (5-10 yr) Photosynthesis (~30) Rootrespiration Fluxes from Chambers et al. Units are MgC ha -1 yr -1 Dead wood excludes trees <10cm DBH CASA

20. Conclusions Radiocarbon provides a measure of time elapsed between photosynthesis and respiration The mean age of C respired from soils ranges from <1 – 20 years Heterotrophically respired C has ages from 3-40 years Comparisons of model with data show that either data are skewed ‘young’ or models are skewed ‘old’; largest problem in low latitude forests

21. Biomass C MgC/ha 180 141 Growth MgC/ha/yr 1.6-2.1 2.2 -3.0 MRT of C (yr) 86-112 47-64 (stock/growth)** Mean age of C (yr)* 260 220 Manaus Santarém