Presentation on theme: "Detecting changes in soil C pools and dynamics by means of stable isotopes and SOM fractionation M.Francesca Cotrufo Dip. Scienze Ambientali Seconda Università."— Presentation transcript:
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
Motivation: “Looking for small changes in large pools and fluxes”
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
Joint workshop “Partitioning soil CO 2 efflux” Villa Orlandi, Capri, Italy Oct 2 nd - 4 th 2004 CARBOEUROPE/COST Action 627
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
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
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
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
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
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.
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
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
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.
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
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
SOM C distribution: Del Galdo et al. SBB, submitted
Effects of land use change on soil C 100 years 20 years
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
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
“Modelling the measurable” “Measuring the modellable”
Rubino et al., in progress Identification of SOM chemical compounds where litter derived C is allocated
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).
I. Del Galdo, G. Battipaglia, T. Bertolini, I. Inglima, M. Rubino, F. Marzaioli, D. Piermatteo, C. Lubritto
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
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