1. Detecting changes in soil C pools and dynamics by means of stable isotopes and SOM fractionation M.Francesca Cotrufo Dip. Scienze Ambientali Seconda Università di Napoli 3 rd CARBOEUROPE Meeting, Finland 2005

2. Motivation: “Looking for small changes in large pools and fluxes”

3. Organic Matter Stabilized soil organic carbon turnover Fresh soil carbon input turnover Soil respiration Litter fall Wood & Litter decomposition Root respiration & decomposition Litter and soil C fluxes

4. Joint workshop “Partitioning soil CO 2 efflux” Villa Orlandi, Capri, Italy Oct 2 nd - 4 th 2004 CARBOEUROPE/COST Action 627

5. Heterotrophic contribution to soil respiration  Results of a meta-analytical review R H /R S = -0.149 ln(RS) +1.569 Subke, Inglima & Cotrufo, GCB Annual Review, 2006

6. Plant and fungal debris Clay microstructures Fungal or microbial metabolites Biochemically recalcitrant organic matter Silt-sized aggregates with microbially derived organomineral associations Microaggregates ~ 50-250  m Particulate organic matter colonized by saprophytic fungi Decomposing roots and detritus become encrusted with mineral particles forming microaggregates Decomposition continues at a slow rate in stable aggregates, due to formation of organomineral associations Eventually, organic binding agents decompose sufficiently for aggregate to be destabilized, accelerating decomposition until new aggregate is formed The SOM aggregation concept

7. Fractionation by size and density scheme Density flotation Light fraction (< 1.85 g cm -3 ) Intra-microaggregate POM (iPOM) Density flotation Light fraction (< 1.85 g cm -3 ) Intra-microaggregate POM (iPOM) >250  m fraction <53  m fraction 53-250  m fraction (m) Wet sieving Micro-aggregate isolator Silt + clay Coarse POM Micro’s (mM) 8 mm sieved soil

8. HYPOTHESES: Afforestation increases aggregate stability and soil C sequestration Elevated [CO 2 ] increases aggregation and SOC pools through higher C input Short-term effects on SOM dynamics after change in land use and exposure to increased [CO 2 ] The EUROFACE project

9. EUROFACE Location: Tuscania, Central Italy (42° 22’ N 11° 48’ E 150 m asl). Climate : Annual rainfall 676 mm, annual mean temperature 15 °C. Project PopFACE (EKV 4- CT96_0657)/ EUROFACE: from 1999 – Establisment of a poplar plantation (P.x euroamericana) on an agricultural region. 6 exsperimental plots, whitin the plantation, each with three poplar species (Populus alba, (clone A), P. nigra, (clone B), e P.x euroamericana, (clone C)); 3 plots are exposed to ambient and 3 to elevated (+200 ppm) concentration of CO 2 with a FACE (Free Air Carbon dioxide Enrichment) operating system

10. Experimental design & methods  4 Vegetation types: Agricultural field (T. aestivum) (A); Poplar plantation (P); clones B (P. nigra) and C (P. x euroamericana) for the FACE system.  6 Replicated samplings along two 50m transects, for A and P @ 0-10 cm depth.  10 Soil cores per sampling plot – Pooled.  4 soil cores, pooled, for clones B and C for each ring of the FACE.  Fractionation for size and density.  Analyses of C content for the total and for all the fractions isolated.

11. Carbon changes in SOM fractions: 1. LAND USE CHANGE EEFFECT C P = C content of soil fractions under poplar plantation C A = C content of respective fractions in the agriculture soils Del Galdo et al. GCB, submitted

12. 2. ELEVATED [CO 2 ] EFFECT C F = C content in FACE soil fractions C C = C content of controls Del Galdo et al. GCB, submitted

13. Past present and future atmospheric [CO 2 ] effects on SOM dynamics Sky Oaks CO 2 -enrichment field station HYPOTHESIS: From pre-industrial level to 750 ppm, the increase in atmospheric [CO 2 ] increases aggregation and SOC pools due to higher plant C input, thus the soil “close” to plants is the most affected.

14. Sky Oaks CO 2 -enrichment field station (Warner Springs, CA, USA)  12 closed chambers within an Adenostoma fasciculatum- dominated chaparral ecosystem, fumigated for 6 years with labelled CO 2 ranging from 250 to 750 ppm in 100 ppm step increments, with a total of two replicate chambers for each of the six treatments.  Three non-fumigated open chambers were selected as control (ambient). Sky Oaks CO 2 -enrichment field station

15.  Soil sampling (0-10 cm) 2 soil cores sampled close to the A. fasciculatum (pooled); 2 soil cores collected far from the plant.  Soil fractionation for size and density;  Analyses of C and  13 C for the totals and for all the fractions isolated Experimental design & methods

16. SOM C distribution: Del Galdo et al. SBB, submitted

17. P<0.005

18. Change in old-new C

19. Effects of land use change on soil C 100 years 20 years

20. Partitioning of soil C into: “new” - C derived from vegetation “old” – native SOC 10-30 cm 0 50 100 150 200 250 C A G C A G C A G C A G C A G C A G C A G M coarse POM mM iPOM_mM Silt&clayM m iPOM_m 0-10 cm 0 50 100 150 200 250 C A G C A G C A G C A G C A G C A G C A G M coarse POM mM iPOM_mM silt&clayM m iPOM_m g C kg-1 sandfree aggregate C= Crop A=Afforested G=Grassland New C Old C Del Galdo et al., GCB, 2003

21. Identify SOC dynamics -1500 -1000 -500 0 500 1000 0-10 cm 10-30 cm M m silt&clay C g m -2 C nuovo C nativo Del Galdo et al., GCB, 2003

22. “Modelling the measurable” “Measuring the modellable”

23. Conventional approach

24. The soil is a dynamic system!

25. Rubino et al., in progress Litter respiration measurements in lab-experiment Soil & P. taeda Soil & C. canadensis Soil & L. styraciflua

26. Rubino et al., in progress Dynamics of  13 C-CO 2 Soil & P. taeda Soil & C. canadensis Soil & L. styraciflua Bulk soil Bulk litters

27. Discrimination during heterotrophic respiration ??? Soil substrate 1:1 J. phaenicia P. lentiscus C. mospeliensis Leaf litter substrate

28. Partitioning of C loss from decomposing litter into soil C input and respired CO 2

30. Rubino et al., in progress Identification of SOM chemical compounds where litter derived C is allocated

31. CONCLUSIONS  Coupling of SOM fractionation by size and density and stable C isotope “labelling” proved to be a useful approach to quantify changes in soil organic C pools “step change” of manipulation studies??  Elevated atmospheric CO 2 appears to increase soil C losses proportionally more than inputs, resulting in a net decrease of soil C. Is it a true effect or rather due to the “step change” of manipulation studies??  After 20 years, afforestation increased the total amount of soil C by 23% and 6% in the 0–10 and in the 10–30cm depth layer, respectively. Forest-derived carbon contributed 43% and 31% to the total soil C storage in the afforested systems in the 0–10 and 10–30cm depths, respectively. Furthermore, afforestation resulted in significant sequestration of new C and stabilization of old C in physically protected SOM fractions, associated with microaggregates (53–250 m) and silt&clay (<53 m).

32. I. Del Galdo, G. Battipaglia, T. Bertolini, I. Inglima, M. Rubino, F. Marzaioli, D. Piermatteo, C. Lubritto

33. APPENDIX C s (t) = C s v (t) + C s n (t)  s (t)C s (t) =  v C s v (t) +  n (t)C s n (t) f’ C s v (t)/C s (t) = [ s (t) -  n (t)]/[ v -  n (t)] f C s v (t)/C s (t) = [ s (t) -  s (0)]/[ v -  s (0)] F r (t) =F r v (t) +F r n (t)  r F r (t) =  r v F r v (t) +  r n F r n (t) F r (t) [ r (t) -  s (0)] = F r v (t) [ v -  n (t)] F r n (t) = k s C s n (t) F r v (t) = F v k v + k s C s v (t) k s = [F r (t)/C s (t)] * [δ r (t)- δ v ]/[δ s (t)- δ v ] C s (t) - C s (0) = C s v (t) - F r s (t) dt C s (t) - C s (0) = C s (t) [δ s (t) - δ s (0)]/[ δ v - δ s (0)] - F r (t) [δ r (t) - δ v ]/[δ s (0) - δ v ] dt C s (t) - C s (0) = f · C s (t) – F r (t) · R s /R t dt

34. SOM DECAY and TURNOVER Six et al. 1998