Detecting changes in soil C pools and dynamics by means of stable isotopes and SOM fractionation

1. 3rd CARBOEUROPE Meeting, Finland 2005 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

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

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

4. CARBOEUROPE/COST Action 627 Joint workshop “Partitioning soil CO2 efflux” Villa Orlandi, Capri, Italy Oct 2nd - 4th 2004

5. Heterotrophic contribution to soil respiration • Results of a meta-analytical review RH/RS = -0.149 ln(RS) +1.569 Subke, Inglima & Cotrufo, GCBAnnual Review, 2006

6. The SOM aggregation concept Microaggregates ~ 50-250 m Plant and fungal debris Fungal or microbial metabolites Particulate organic matter colonized by saprophytic fungi Biochemically recalcitrant organic matter Silt-sized aggregates with microbially derived organomineral associations Clay microstructures 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

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

8. Short-term effects on SOM dynamics after change in land use and exposure to increased [CO2] The EUROFACE project • HYPOTHESES: • Afforestation increases aggregate stability and soil C sequestration • Elevated [CO2]increases aggregation and SOC pools through higher C input

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, (cloneA), P. nigra, (clone B), e P.x euroamericana, (clone C)); 3 plots are exposed to ambient and 3 to elevated (+200 ppm) concentration of CO2with 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 CP = C content of soil fractions under poplar plantation CA = C content of respective fractions in the agriculture soils Del Galdo et al. GCB, submitted

12. 2. ELEVATED [CO2] EFFECT CF = C content in FACE soil fractions CC = C content of controls Del Galdo et al. GCB, submitted

13. Sky Oaks CO2-enrichment field station Past present and future atmospheric [CO2] effects on SOM dynamics • HYPOTHESIS: • From pre-industrial level to 750 ppm, the increase in atmospheric [CO2]increases aggregation and SOC pools due to higher plant C input, thus the soil “close” to plants is the most affected.

14. Sky Oaks CO2-enrichment field station Sky Oaks CO2-enrichment field station (Warner Springs, CA, USA) • 12 closed chambers within an Adenostoma fasciculatum-dominatedchaparral ecosystem, fumigated for 6 years with labelled CO2 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).

15. Experimental design & methods • 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 d13C for the totals and for all the fractions isolated

16. 4000 3000 ) SC -2 2000 m C (g m M 1000 0 control 250 350 450 550 650 750 CO (ppm) 2 Close to plant 4000 3500 3000 ) SC 2500 -2 m 2000 C (g m 1500 M 1000 500 0 control 250 350 450 550 650 750 CO (ppm) 2 Far from plant 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. 250 250 0-10 cm 10-30 cm New C 200 200 Old C 150 150 100 100 50 50 0 0 C A G C A G C A G C A G C A G C A G C A G C A G C A G C A G C A G C A G C A G C A G M M coarse coarse POM POM mM mM iPOM_mM iPOM_mM silt&clayM Silt&clayM m m iPOM_m iPOM_m Partitioning of soil C into:“new” - C derived from vegetation “old” – native SOC g C kg-1 sandfree aggregate C= Crop A=Afforested G=Grassland Del Galdo et al., GCB, 2003

21. C nuovo C nativo 0-10 cm10-30 cm 1000 500 C g m-2 0 -500 -1000 M m silt&clay M m silt&clay -1500 Identify SOC dynamics Del Galdo et al., GCB, 2003

22. “Modelling the measurable” “Measuring the modellable” Del Galdo et al., GCB, 2003

23. Conventional approach

24. The soil is a dynamic system!

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

26. Soil & P. taeda Soil & C. canadensis Soil & L. styraciflua Dynamics of d13C-CO2 Bulk soil Bulk litters Rubino et al., in progress

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

28. Partitioning of C loss from decomposing litter into soil C input and respired CO2

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

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 • Elevated atmospheric CO2 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 mm) and silt&clay (<53 mm).

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

33. APPENDIX Cs(t) = Csv(t)+ Csn(t) s(t)Cs(t)= vCsv(t)+n(t)Csn(t) f’ º Csv(t)/Cs(t) =[s(t)- n(t)]/[v - n(t)] f º Csv(t)/Cs(t) =[s(t)- s(0)]/[v - s(0)] Fr(t) =Frv(t)+Frn(t) rFr(t) = rvFrv(t)+rnFrn(t) Fr(t) [r(t)- s(0)] = Frv(t) [v - n(t)] Frn(t) = ksCsn(t)Frv(t) = Fvkv + ksCsv(t) ks = [Fr(t)/Cs(t)] * [δr(t)- δv]/[δs(t)- δv] Cs(t) - Cs(0)= Csv(t) - ò Frs(t) dt Cs(t) - Cs(0) = Cs(t) [δs(t)- δs(0)]/[ δv - δs(0)] - ò Fr(t) [δr(t)- δv]/[δs(0) - δv] dt Cs(t) - Cs(0) = f · Cs(t) – ò Fr(t) · Rs/Rt dt

34. SOM DECAY and TURNOVER Six et al. 1998