Mineral-organic Associations: Formation, properties, and functions

Transcription

1 Summer-School, Krasnojarsk Mineral-organic Associations: Formation, properties, and functions Robert Mikutta, Institute of Soil Science, Hannover, Germany Introduction >1 Gt OC in association with minerals Assuming ~15 Gt OC (2 m depth, excluding Histosols) and >6% of total soil OC being mineral-associated, Data: Soil Taxonomy, Batjes (1996) Eur. J. Soil Sci. 47, Global importance 1

2 Introduction Under extreme conditions wet (MAP 3-6 mm) cold (MAT -12 C) % mineral-associated OC n = 22 n = 3 n = 15 A, AO, AE B, BC C % mineral-associated OC n = 25 n = 1 n = 25 n = 26 Ajj A/AB B/BCg/Cg PF New Zealand, 12 Kyr chronosequence Siberian tundra soils Global importance Introduction Clay minerals SSA 1-8 m 2 g -1 PZC <5 The reaction partners 2

3 Introduction Metal (hydr)oxides SSA 5-5 m 2 g -1 PZC 7-9 The reaction partners Introduction and organic matter non-humic humic Size and complexity The reaction partners 3

4 Concepts & Ideas Concepts & Ideas Concepts & Ideas Regosols Andosols Luvisols Jahn et al. (1992) Miner. Petrogr. Acta 35A, Mineral-transformations 4

5 Concepts & Ideas Chronosequence at Hawaiian Islands.3 4,1 Kyrs Phenols (mg/g MOC) Phenols Lignin phenols H BA 2H BA 3H BA 4H BA 3,5diH BA Site age (kyr) Carbohydrates (mg/g MOC) Sugars Xyl Ara Rib Rha Fuc Fru Man Gal Glu GluA GalA Site age (kyr) BA = benzoic acid Selectivity in organic matter accumulation Mikutta R. et al. (29) Geochim. Cosmochim. Acta 75, Concepts & Ideas Well-aerated acidic soils density separates, d >1.6 Mg m 3 Neutral alkaline soils density separates, d >1.6 Mg m R 2 = R 2 =.85 OC [g kg -1 ] OC [g kg -1 ] topsoils illuvial subsoils topsoils Fe DCB [g kg -1 ] Oxide-free clay [g kg -1 ] Kaiser K & Guggenberger G (2) Org. Geochem. 31, Selectivity in organic matter accumulation 5

6 Concepts & Ideas 2 Permafrost soils (Kolyma lowlands) density separates, d >1.6 Mg m 3 No correlation with total pedogenic Fe (DCB-extractable Fe)! OC [g kg -1 ] R 2 =.8 P <.1 Reason: Reductive dissolution of Fe(III) oxides 4 Topsoil and subsoil Clay content [g kg -1 soil] Selectivity in organic matter accumulation Concepts & Ideas Mineral specific surface area maximum C sorption m 2 g 1 mg C m 2 mg C g 1 Kaolinite Illite Vermiculite Smectite Hydroxy-interlayered clays amorphous Al(OH) Gibbsite Ferrihydrite Haematite Goethite Allophane / Imogolite Kaiser K & Guggenberger G (2) Org. Geochem. 31, Selectivity in organic matter accumulation 6

7 Concepts & Ideas EA Bh Bs bulk soil POM MOM Bw C1 C2 Data: Waldstein Podzol Klaus Kaiser Radiocarbon age [years B.P.] Binding mechanisms Surface loading and pore clogging Multilayer formation Minerals and organic matter stabilization mechanisms Concepts & Ideas Organic matter adsorption to different mineral surfaces K aff, L/kg Sorption affinity Clay minerals Fe oxide desorbable OC, % Desorption Clay minerals Fe oxide Cation bridges Covalent bonds V = Vermiculite, P = Pyrophyllite, G = Goethite, Cation bridges Covalent bonds Mineral surface reactivity and bonding mechanisms 7

8 Concepts & Ideas Biological stability of mineral-associated OC Rate constant K1 [d -1 ] K1 K2 r 2 =.86; P < Initial ph: Rate constant K2 [1-3 d -1 ] desorbable OC [%] ph after 9 d of incubation Abiotic conditions control binding strength and thus mineralization Mikutta R. et al. (27) Geochim. Cosmochim. Acta 71, Mineral surface reactivity and bonding mechanisms Concepts & Ideas OC sorbed [mg m -2 ] ph = 4. DOC = 33 mg l 1 with sorbed organic matter 1.9 mg OC m OC added [mg m -2 ] 2 nm High C loading goethite without organic Low matter biochemical stability with sorbed organic matter.9 mg OC m 2 Low C loading High biochemical stability 2 nm Kaiser and Guggenberger (27) Eur. J. Soil Science 58, Organic matter loading and octopus effect 8

9 Concepts & Ideas Multilayer model Sollins et al. (26) Soil Biol. Biochem. 38, Kleber et al. (27) Biogeochem. 85, 9 24 Organization of organic coatings at mineral surfaces Concept & Ideas Hydration of macromolecular OM (e.g., mucilage, extracellular polymeric substances, humic compounds) H 2 O H 2 O H 2 O H 2 O Hydration time Organic matter flexibility: hydration effects 9

10 Concept & Ideas Phosphate sorption and organic C desorption Phosphate sorbed, µmol g h hydration time 17 h hydration time Time, h Phosphate faster accessible to external mineral sufaces after longer hydration time Organic matter flexibility: hydration effects Mikutta C. et al. (26) Geochim. Cosmochim. Acta 7, Mineral-microbe interactions The Bio Mineral surfaces as microbial microreactors 1

11 Mineral-microbe interactions Handbook of Soil Science Chenu and Plante 26, Eur. J. Soil Sci., 57, Mineral-microbe associations in soils Fortin and Langley 25, Earth-Sci. Rev. Mineral-microbe interactions Mineral effects on C and P cycles well recognized but Renneberg et al. (29) Plant Biol. 11, 4 23 N mineralized (µg/g dry wt.) R 2 = N in heavy fraction (%) Re-drawn from Sollins et al. (1984) Soil Biol. Biochem. 16, Knicker (211) Soil Biol. Biochem. 43, Mineral-bound OM as substrate for microorganisms 11

12 Concepts & Ideas Chronosequence at Franz Josef Glacier (NZ) Kyrs OC stocks (kg m -2 ) MOM POM ON stocks (kg m -2 ) MOM POM Substrate age (Kyr) Substrate age (Kyr) Mineral-bound OM as substrate for microorganisms Mineral-microbe interactions % % A B C D E ß-Proteobacteria A quartz + montmorillonite B quartz + illite C quartz + ferrihydrite D quartz + montmorillonite + illite E quartz + montmorillonite + charcoal F quartz + illite + ferrihydrate G quartz + illite + boehmite H quartz + illite + ferrihydrate + charcoal Incubation Acidobacteria time /months Incubation time /months Mineral surfaces cause modification of microbial community structure Artificial soils with added sterile manure Selective colonization of mineral surfaces by r- (ß-proteobacteria) and K-strategiest (acidobacteria) r type: rapid growth under conditions of high resource availability K type: lower growth rates, but higher substrate affinity Kandeler et al. (in prep.) Mineral surfaces as drivers for microbial community separation 12

13 Mineral-microbe interactions Extracellular polymeric substances (EPS) Contribution to mineral-associated OM? idealhomegarden Dohnalkova et al., 211 Microbial-derived organic matter Mineral-microbe interactions Extracellular polymeric substances (EPS) from Bacillus subtilis adsorbed to Al hydroxide 12 Adsorbed EPS constituents (%) Initial EPS-C = 1 mg/l ph = 4.5 EPS-C EPS-N EPS-P EPS-S Molar Al:C ratio Mikutta, R. et al. (211) Geochim. Cosmochim. Acta 75, Microbial-derived organic matter 13

14 Mineral-microbe interactions Charge properties of Fh and its association with polysugars EM (1-8 m 2 /V/s) Fh PGA-Fh copr ph Coprecipitates are net negatively charged Alginate-Fh copr. Stability of suspensions at ph 7: Fh = low, coprecipitates = high Charge effects of microbial compounds PZC Pure Fh 7.2 PGA-Fh ~2 Alginate-Fh ~2 Mikutta, C. et al. (28) Geochim. Cosmochim. Acta 72, Introduction Formation of mineral-organic associations: Coprecipitation 14

15 Structure & Reactivity Illite 115 m 2 g -1 Ferrihydrite on Illite 133 m 2 g -1 Kaolinite 7 m 2 g -1 Goethite on kaolinite 14 m 2 g -1 Secondary oxide precipitation modify surface properties Introduction 15

16 Structure & Reactivity Organic C (mg/g) Initial OC 5 mg/l ph Al.1.1+Al.1.1+Al 1 Adsorption Coprecipitation Blue: Aromatic Oa Green: Sugar-rich Oi Adsorption versus coprecipitation Structure & Reactivity Field evidence: Sediments Coprecipitation / adsorption and organic matter stabilization Lalonde et al. (212) Nature 483,

17 Structure & Reactivity Field evidence: Hawaiian Islands 4 Topsoil Subsoil young 3 4 kyr V OM /V mineral kyr 2 kyr old Soil ph (H 2 O) Adsorption versus coprecipitation Mikutta R. et al. (29) Geochim. Cosmochim. Acta 75, Structure & Reactivity.3 Field evidence: Permafrost soils.25 Fe p +Al p (mmol g -1 ) y =.2 ±. x r 2 =.95; P< Mineral-associated OC (mmol g -1 ) Adsorption versus coprecipitation Mikutta R. et al. (214) Eur. J. Soil Sci. (submitted) 17

18 Structure & Reactivity Surface properties at varying metal:c ratios SSA [m²/g] Ferrihydrite Adsorption complexes 1 R² =.99 M:C.1 M:C R² = OC content [mg/g] Organic matter shapes mineral phases Structure & Reactivity Organic matter disturbs crystallite formation Organic matter shapes mineral phases 18

19 Structure & Reactivity A B C A B C Increase in Fe oxide crystallinity not the total amount but position of phenolic groups influence HFO crystallization Mikutta C. (211) Geochim. Cosmochim. Acta 75, Organic matter shapes mineral phases Structure & Reactivity Dissolution reactions Single ligand system: 1.5 mm oxalate, Fe tot =.1 g/l, ph 4 5 Fe aq (µmol/fe tot ) Fast Slow Initial Kinetic Rate: 9 mmol/mol Fe/min Initial Kinetic Rate:.3 mmol/mol Fe/h Fe/C = 1 Fe/C = time (min) Molar Fe/C ratio controls dissolution processes 19

20 Structure & Reactivity Dissolution reactions 1 Single ligand system: 1.5 mm oxalate, Fe tot =.1 g/l, ph 4 R app dissolution rate (mmol mol -1 Fe h -1 ) 1 1 Oa M/C =.1 Oa M/C = 1 Oi M/C = 1 Oi M/C = Fe structural /Fe org Fe org = pyrophosphate-extractable Fe (with ultracentrifugation 3. g for 3 h) Fe complexation mode controls dissolution processes Structure & Reactivity Dissolution reactions 6 5 Oi % Aromatic Carbonyl /Carboxyl Fe aq (µmol/fe tot ) Oa Oi Oa time (min) Humified OM (more acidic and aromatic) binds more strongly and blocks surface sites more efficiently than litter-derived OM ( Surface passivation ) Influence of OM source on dissolution kinetics 2

21 Structure & Reactivity Dissolution reactions (especially relevant in permafrost soils) Fe(II) aq (mm) Coprecipitation Oa Oi EPS Ferrihydrite Shewanella putrefaciens Flavins Time (days) Humified OM (more acidic and aromatic) accelerates Fe reduction Electron shuttling Influence of OM source on dissolution kinetics Structure & Reactivity Dissolution reactions Fe(II) aq (mm) Coprecipitation Oa Oi EPS Ferrihydrite Adsorption Oa Oi EPS Ferrihydrite 2 mg OC/g Time (days) Time (days) Almost similar reactivity; higher in case of coprecipitated Oa- and EPS-C Influence of OM source on dissolution kinetics 21

22 Structure & Reactivity Biodegradation 12 1 Adsorption Solution phase Solid phase Mineralized OC (%) Pure EPS Initial molar Al:C ratio %OC Coprecipitation / adsorption and organic matter stabilization Structure & Reactivity Biodegradation 12 1 Coprecipitation Solution phase Solid phase Mineralized OC (%) Pure EPS Initial molar Al:C ratio Mikutta, R. et al. (211) Geochim. Cosmochim. Acta 75, Coprecipitation / adsorption and organic matter stabilization 22

23 Structure & Reactivity DOM adsorption to Al hydroxide (Schneider et al. 27, Geochim. Cosmochim. Acta) Artificial metal-organic complexes (Boudot et al. 1989, Soil Biology Biochem.) Mineralized OC (% of initial OC) 6 Oi beech Oa beech Oi spruce Oa spruce %C 1-3%C Mineralized OC (% of initial OC) 6 Al-fulvic acid Al-humic acid Fe-humic acid Fe-fulvic acid %C 6-9%C Solid-to-solution ratio molar metal:c Increasing surface OC loading Increasing surface OC loading Coprecipitation / adsorption and organic matter stabilization Take-home messages Minerals control OM accumulation and stabilization in many soils Mineralogy changes in days to millennia and thus also the capability to accumulate OM Minerals accumulate OM selectively and act as nutrient sink and source (organic N and P) Besides adsorption, coprecipitation of OM with metals (Fe, Al, Ca) plays a role in many soil ecosystems Minerals reduce OM mineralization but never impair the decomposition completely Mineral-associated OM modifies mineral reactivity (dissolution reactions) 23

24 Final Thank you Labour input: many, many (PhD students, technicians, collaborators) Intellectual input: many 24