CENTREFORESTALTECNOLÒGICDE CATALUNYAPinares secundarios en cultivos abandonados:Evolución del stock de carbono edáficoPere Rovira & Aida SalaSolsona
Broadleaf (18)Conifer (65)< 900 mm (8)900 - 1200 (17)1200 - 1500 (24)> 1500 mm (12)-40 -20 0 20 40Soil carbon change (%)Guo L.B. & Gifford R.M. (2002). Global Change Biology 8, 345-360.From crop abandon to forest: changes in soil C stock
Cardona (Barcelona): crop abandonment and secondary pine stands development
The replacement of crops by secondary forest, in the studiedarea of Cardona (Barcelona, Spain):1. Does it result in a net carbon sequestration?2. Where do the changes in the total C stock occur?3. How the C stock is affected by these changes?- Biochemical quality (labile / recalcitrant fractions)- Physical protection (POM / organomineral complexes)4. How the stability of the accumulated C is affected by thesechanges?Defining challenges
Plot location: systematic comparison of aerial photographs1956 2009
Delimitation of plot typesType Dominant species 1956 2009 FeaturesCrop Triticum aestivum Crop Crop TerracingNew forest 1 Pinus nigra Crop Forest TerracingNew forest 2 Pinus nigra Forest Forest TerracingOld forest Pinus nigra Forest Forest No terracing; nevercropped apparentlyIn all cases:Marl-type substrate, rich in carbonates, lclay-loam textures.
Organic horizons (litter): L, F and Hsampled with aluminum cylinders.8 cylinders per plot(forest plots only)Mineral soil down to 30 cm:sampled with prismatic core samplers.5 cores per forest plot,4 cores per agricultural plot.Soil sampling
0151530Soil samplingDepth, cm
Organic horizonsMineral soil (0-30 cm)kgCm-202468CropsNew forest 1New forest 2Old forestQuantifying total C stock, down to 30 cm depth-2Carbon sequestration potential, on the very long term: about 3 kg C mAbout 1 kg in the mineral soil, about 2 kg in the litter horizonsDeep soil (> 30 cm depth): much more difficult to predict.
Incubation under standard conditions:25ºC, optimal humidityC respired after 30 days (mg per g OC)60 70 80 90 100 110Depth(cm)-100102030CropsNew forests 1New forests 2Old forestsLitterMineral soilDifferences not significant overallHow does stability of soil C change?
- Increases in the biochemical quality- Decreases in the physical protection- Both- ...?Why?
Evaluation of biochemical qualitySoil sampleRecalcitrantresidueHydrolysate I Hydrolysate II1M HCl3 h6M HCl24 hRecalcitrance index =Unhydrolyzed CTotal C
Old forests0 2 4 6 8 10New forests 2Total organic Carbon (% w/w)0 2 4 6 8 10020406080100New forests 1Crops0.0 0.5 1.0 1.5 2.0RecalcitranceindexforCarbon(%)020406080100Recalcitrance is related to OC content
Hydrolysis with hydrochloric acidRecalcitrance index for Carbon (%)25 30 35 40 45 50 55 60Depth(cm)-100102030CropsNew forests 1New forests 2Old forestsLitterMineral soilRecalcitrance is related to land useChanges in OC biochemical quality do not explain its lower stability in forests.
OC in the < 20 µm fraction (% of total OC)30 40 50 60 70 80 900 - 5 cm5 - 15 cm15 - 30 cmabbOverall, physical protection increases with depth
Mineral soil (first cm not included)OCinthe<20µmfraction(%oftotalOC)2030405060708090CropsNew forest 1New forest 2Old forestP < 0.001a b b bPhysical protection as related to land useOverall, the replacement of crops by forests results in a decreasein the degree of physical protection of soil organic matter.
Organic carbon (% w/w)0 1 2 3 4 5Carbonin<20µmfraction(%oftotalOC)455055606570758085 CropsNew forests 1New forests 2Old forestsR 2= 0.2026 **Physical protection as related to OC content of the horizon
Physical protection of soil carbonOC in the < 20 µm fraction (% of total OC)20 40 60 80 100Depth(cm) 051015202530CropsNew forest 1New forest 2Old forestPhysical protection as related to land use and position within the soil profile
- Evolution of nitrogen forms.- Evolution of phosphorus forms and availability.- Evolution of inorganic C (carbonates).- Chemical fertility: Cation exchange capacity, exchangeable cations...etc.To be continued!Work under way...
Thanks for your attention!This research was performed under the framework of the CRONOCARB project,funded by the Ministerio de Ciencia y Tecnología, Spain.