UNIVERSITYOFNAPOLI"FEDERICOIIAGRICULTURALEACULTYD.LS.S.P.A.P.ASoil chemistry departmentSoil Organic Matter dynamics13C labelled organic materialTMAHthermochemolysisDr.Riccardo Spaccini
UNIVERSITY OF NAPOLI “FEDERICO II” AGRICULTURAL FACULTY D.I.S.S.P.A.P.A. Dr. Riccardo Spaccini Soil chemistry department Soil Organic Matter dynamics - TMAH thermochemolysis - 13C labelled organic material
one of the pressing problems in agro-ecosystems is representedby the continuous loss of soil organic matter contenta part the immediate effect on plant productivity the lowering ofSOM level lead to a long term decrease of overall soil chemicaland biochemical fertility and soil aggregate stability (soil erosion)all these effects have as a feed back consequence, the furtherincrease of SOC losses: agricultural activities have nowadays asignificant contribute to green-house gas emissions in the earthatmospherein 1997 the estimation for the current loss rate from virgin soilsconvertedto intensive agricoltural exploitation was around0.9 x 1015 g C yr-ldifferent practices are therefore currently applied in order toreduce, in the short/medium terms, the decrease of SOC contentand to produce a long term restoring or improvement of SOM level
one of the pressing problems in agro-ecosystems is represented by the continuous loss of soil organic matter content a part the immediate effect on plant productivity the lowering of SOM level lead to a long term decrease of overall soil chemical and biochemical fertility and soil aggregate stability (soil erosion) all these effects have as a feed back consequence, the further increase of SOC losses: agricultural activities have nowadays a significant contribute to green-house gas emissions in the earth atmosphere in 1997 the estimation for the current loss rate from virgin soils converted to intensive agricoltural exploitation was around 0.9 x 1015 g C yr-1 different practices are therefore currently applied in order to reduce, in the short/medium terms, the decrease of SOC content and to produce a long term restoring or improvement of SOM level
integration or replacement of mineral fertilizers with organic materialssuch as green manure, animal manure, pig slurry, recycled organicbiomasses etc.among SOM pools an important component are represented by humicmaterials: this colloidal organic fraction largely affect all the variousaspect of long term soil fertility, moreover acting as a long term sinkof soil organic matterhumic substances, such as humic acids and humin represent in fact themost persistent pool for SOC accumulation, through the selectivepreservation of recalcitrant material and the close interaction withfinestsoil fractionshumic material is believed to play a fundamental role in the stableincorporation of more labile organic compounds released from rootexudates, plant litter and microbial activity, thereby increasing SOMsequestration and reducing the OC mineralization
- reconversion of marginal areas to less exploiting crops and reforestation of previous cleared virgin soils among SOM pools an important component are represented by humic materials; this colloidal organic fraction largely affect all the various aspect of long term soil fertility, moreover acting as a long term sink of soil organic matter humic substances, such as humic acids and humin represent in fact the most persistent pool for SOC accumulation, through the selective preservation of recalcitrant material and the close interaction with finest soil fractions - replacement of current soil management methods with less intense exploitation techniques such as minimum tillage, zero tillage and fallow - integration or replacement of mineral fertilizers with organic materials such as green manure, animal manure, pig slurry, recycled organic biomasses etc. humic material is believed to play a fundamental role in the stable incorporation of more labile organic compounds released from root exudates, plant litter and microbial activity, thereby increasing SOM sequestration and reducing the OC mineralization
"Organic carbon sequestration through protection by humic substances'ObjectiveStudy the effect of humified organic matter on the mineralizationof labile organic compound in soila short chain alcohol (2 decanol) was labelled with 13C isotope andused for soil incubation to study the OC mineralizationthe 13C labelled alcohol was added to soil either alone or inmixture with two humic acids extracted from lignite and fromrecycled organicbiomassthe mineralization of labelled alcohol was followed for 6 monthsin all soil treatments either in bulk soils and in soil-size fractions,determining also the final incorporation of labelled compounds insoil humic substances
“Organic carbon sequestration through protection by humic substances” Objective Objective Study the effect of humified organic matter on the mineralization of labile organic compound in soil a short chain alcohol (2 decanol) was labelled with 13C isotope and used for soil incubation to study the OC mineralization the 13C labelled alcohol was added to soil either alone or in mixture with two humic acids extracted from lignite and from recycled organic biomass the mineralization of labelled alcohol was followed for 6 months in all soil treatments either in bulk soils and in soil-size fractions, determining also the final incorporation of labelled compounds in soil humic substances
Why using 13C labelled compoundthe use of organic material labelled with 13C isotope is a useful tool forthe analysis of SOM dynamics and of OC mineralizationthe enzymatic systems involved during photosynthesis in plant C fixationdiscriminate against the 13C isotope, reducing the 13C content in plant tissues;the amount of 13C is indicated as and it is determined (with IR-MS)comparing the ratio 13C/12C of the sample and that of a reference standard(13C/12C)sample -(13C/12C)reference8× 1000(13C/12C)referencethe 13C content in the various plant species change with differentphotosynthetic pathway:-C3 plants (wheat) (Calvin cycle)havean average 13C content 8=-27%o-C4 plants (corn) (Hatch & Sluck cycle) have average 13C content 8= -14%o-CAM plants have an average 13C content = C4 plants(facultative CAM have a 13C content S =-14%o → -27%o)
the use of organic material labelled with 13C isotope is a useful tool for the analysis of SOM dynamics and of OC mineralization the enzymatic systems involved during photosynthesis in plant C fixation, discriminate against the 13C isotope, reducing the 13C content in plant tissues; the amount of 13C is indicated as δ and it is determined (with IR-MS) comparing the ratio 13C /12C of the sample and that of a reference standard the 13C content in the various plant species change with different photosynthetic pathway: -C3 plants (wheat) (Calvin cycle) have an average 13C content δ= -27‰ -C4 plants (corn) (Hatch & Sluck cycle) have average 13C content δ= -14‰ -CAM plants have an average 13C content δ ≅ C4 plants (facultative CAM have a 13C content δ = -14‰ ÷ -27‰) δ = (13C /12C)sample–(13C /12C)reference reference (13C /12C)reference reference × 1000 Why using Why using 13C labelled compound labelled compound
since there is not a net or significative microbial discrimination of 13Cduring microbial degradation and microbial synthesis the 13C abundance ofSOM reflect the composition of the plant species cultivatedby adding to soil an organic material with different 13C content it istherefore possible to label the new entering SOC and differentiate betweenold and new organic material, thereby following both processes of OCaccumulation and mineralizationplant speciesplant species S13C BPos813C A-oXSAoldSOCnew SOC8A<8X<SB0timeThe amount of recent SOC is calculated as percentage(8X - SA)% SOC× TOC(%)recent(8B - SA)
by adding to soil an organic material with different 13C content it is therefore possible to label the new entering SOC and differentiate between old and new organic material, thereby following both processes of OC accumulation and mineralization since there is not a net or significative microbial discrimination of 13C during microbial degradation and microbial synthesis the 13C abundance of SOM reflect the composition of the plant species cultivated plant species plant species δ13C A SOC content (%) 100 0 δA The amount of recent SOC is calculated as percentage % SOC recent = ( δX– δA) ( δB – – δA) × TOC(%) old SOC old SOC δ X new SOC new SOC time plant species plant species δ13C B δA < δX X < δ B
in long term field experiment the shift between old and recent SOM is obtainedby “natural labelling"' replacing the previous cultivated plant species withanother crop with different e.g. wheat (C, plant) replaced with corn (C4plant)in short term laboratory incubation experiment, synthesized labelledorganic compound, with a significant different 8, are likely used inorder to have a rapid shift between old and recent SOMlabelledorganiccompoundsSB8B-8A >100%0100(%) oXSAnewSOColdSOC8A<8X<8B0timedays/weeks
C3plantδA C4plant δB δA old SOC old SOC δX new SOC new SOC time T O C c o n t e n t (% ) 100 0 δA 100 A > 100‰ days/weeks in short term laboratory incubation experiment, synthesized labelled organic compound, with a significant different δ, are likely used in order to have a rapid shift between old and recent SOM
"Organic carbon sequestration through protection by humic substancesObjectiveStudy the effect of humified organic matter on the mineralizationof labile organic compound in soila short chain alcohol (2 decanol) was labelled with 13C isotope andused for soil incubation to study the OC mineralizationthe 13C labelled alcohol was added to soil either alone or inmixture with two humic acids extracted from lignite and fromrecycled organicbiomassthe mineralization of labelled alcohol was followed for 6 monthsin all soil treatments either in bulk soils and in soil-size fractions.determining also the final incorporation of labelled compounds insoil humic substances
“Organic carbon sequestration through protection by humic substances Objective Objective Study the effect of humified organic matter on the mineralization of labile organic compound in soil a short chain alcohol (2 decanol) was labelled with 13C isotope and used for soil incubation to study the OC mineralization the 13C labelled alcohol was added to soil either alone or in mixture with two humic acids extracted from lignite and from recycled organic biomass the mineralization of labelled alcohol was followed for 6 months in all soil treatments either in bulk soils and in soil-size fractions, determining also the final incorporation of labelled compounds in soil humic substances
13C-labelling of 2-decanol13C labelled 2-decanol was synthesized in our laboratory by aGrignard reaction between nonanoic aldehyde and a 13C-labelled methyliodide with a yield of 76.3% as reported in thefollowing scheme:ether13CH,Mgl13CH,I + MgC, aldehydeOMgCether→CH,-(CH2)-C_13CH3CHs-(CH2)-° + 13CH,MglHHOHOMglH,.O+CH3-(CH2)-C-13CHCH3-(CH2)-C-13CH3HH13C labelled 2-decanol = 13C2-dec
13C-labelling of 2-decanol 13C labelled 2-decanol was synthesized in our laboratory by a Grignard reaction between nonanoic aldehyde and a 13Clabelled methyliodide with a yield of 76.3% as reported in the following scheme: 13CH3I + Mg I + Mg ether 13CH3 3MgI ether 13CH3MgI CH3 3 -(CH2 )7 - C - 13CH 3 OMgI H CH3 -(CH2 )7 - C - 13CH 3 OMgI H H3 O + CH3 3 -(CH2 2 )7 7 -C + H O C9aldehyde aldehyde CH3 -(CH2 )7 - C - 13CH 3 OH H 13C labelled labelled 2 -decanol decanol = 13 C 2 -dec
Computer simulation of 2-decanol NMR spectra/8102370501060402030OH1CH,-CH,-CH,-CH,-CH,-CH,-CH,-CH,-CH-13CH,95384210761910NMR spectra of 13C2-decanol8X3250704020601030
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH-13CH3 70 60 50 40 30 20 10 70 60 50 40 30 20 10 7 6 5 4 3 2 1 OH 10 9 8 10 10 2 2 9 9 1 1 4 4 3 3 8 8 Computer Computer simulation simulation of 2-decanol decanol NMR spectra spectra NMR spectra spectra of 13C2-decanol decanol