1. A.EKBLAD & P.HÖGBERG Plant and Soil 219: 197-209, 2000
Analysis of δ13C of CO2 distinguishes between microbial respiration of added C4-sucrose and other soil respiration in a C3-ecosystem
A.EKBLAD & P.HÖGBERG
Plant and Soil 219: , 2000
J.Michael MÜHLEGGER Stable Isotope Tracing 2009/2010

2. Background δ13C difference between C3 plants and C4 plants
δ13C3: ‰; δ13C4: ‰ relative to V-PDB
Soil respiration (roots, mycorrhizal fungi, rhizosphere microorganisms and litter decomposing microorganisms)
Rapid increase of respiration of C3-C
Mühlegger, Ekblad & Högberg, 2000

3. Aims of study Increase in C3-respiration: artefact or true increase?
Are roots or microbes the main contributors?
Respire mycorrhizal roots the added C4-sucrose?
Mühlegger, Ekblad & Högberg, 2000

4. Material & Methods 7 experiments in total
In situ measurements in boreal forests Respiration measurement on sieved mor- layer (root free) and in forest (with roots)
Monitoring of soil respiration after adding C4-sucrose in field and laboratory
Mühlegger, Ekblad & Högberg, 2000

5. Material & Methods
Experiment 1: applying C3-sucrose, C4-sucrose and H2O to sieved mor-layer
Experiment 2-5: time course experiments in laboratory and in forests
Experiment 6: inoculated roots vs. non-inoculated roots
Experiment 7:10 repeated samplings of basal respiration from a single point
Mühlegger, Ekblad & Högberg, 2000

6. Results
Experiment 1
no difference between control (H2O), C3-sucrose and isotopic composition of C3-sucrose
δ13C after addition of C4-sucrose intermediate between value of C4-sucrose itself and value of pure C3-respiration
Mühlegger, Ekblad & Högberg, 2000

7. Results Experiments 2 and 3
Mühlegger, Ekblad & Högberg, 2000

8. Results Experiments 4 and 5
Mühlegger, Ekblad & Högberg, 2000

9. Results Experiment 6: Experiment 7:
Wether either mycorrhizal or non mycorrhizal roots respire added sucrose
Experiment 7:
Mühlegger, Ekblad & Högberg, 2000

10. Discussion
C4-sucrose-induced increase in respiration of endogenous C3-C
No artefact
No increased respiration of root-related carbon
No exchange during CO2 diffusion
Accelerated turnover of C in microbial biomass
Mühlegger, Ekblad & Högberg, 2000

11. Pros and Cons of method Pros of method
No artificial labelling, no radiation
Inexpensive
Cons of method
Low sensitivity because of small differences in δ13C values between C3 and C4 plants
Mühlegger, Ekblad & Högberg, 2000