Only small changes in soil organic carbon and charcoal concentrations found one year after experimental slash-and-burn in a temperate deciduous forest

International audienceAnthropogenic fires affected the temperate deciduous forests of Central Europe over millennia. Biomass burning releases carbon to the atmosphere and produces charcoal, which potentially contributes to the stable soil carbon pools and is an important archive of environmental history. The fate of charcoal in soils of temperate deciduous forests, i.e. the processes of charcoal incorporation and transportation, and the effects on soil organic matter are still not clear. In a long-term experimental burning site, we investigated the effects of slash-and-burn and determined soil organic carbon, charcoal carbon and nitrogen concentrations and the soil lightness of colour (L*) in the topmost soil material (0?1, 1?2.5 and 2.5?5 cm depths) before, immediately after the fire and one year after burning. The main results are that (i) only few charcoal particles from the forest floor were incorporated into the soil matrix by soil mixing animals. In 0?1 cm and during one year, the charcoal C concentrations increased only by 0.4 g kg?1 and the proportion of charcoal C to SOC concentrations increased from 2.8 to 3.4%; (ii) the SOC concentrations did not show any significant differences; (iii) soil lightness significantly decreased in the topmost soil layer and correlated with the concentrations of charcoal C (r=-0.87**) and SOC (r=?0.94**) in samples 0?5 cm. We concluded that the soil colour depends on the proportion of aromatic charcoal carbon in total organic matter and that Holocene burning could have influenced soil charcoal concentrations and soil colour

Soil organic

[1] We quantified the effects of repeated, seasonal fires on soil organic carbon (SOC), black carbon (BC), and total N in controls and four fire treatments differing in frequency and season of occurrence in a temperate savanna. The SOC at 0-20 cm depth increased from 2044 g C m À2 in controls to 2393-2534 g C m À2 in the three treatments that included summer fire. Similarly, soil total N (0-20 cm) increased from 224 g N m À2 in the control to 251-255 g N m À2 in the treatments that included summer fire. However, winter fires had no effect on SOC or total N. Plant species composition coupled with lower d 13 C of SOC suggested that increased soil C in summer fire treatments was related to shifts in community composition toward greater relative productivity by C 3 species. Lower d 15 N of soil total N in summer fire treatments was consistent with a scenario in which N inputs > N losses. The BC storage was not altered by fire, and comprised 13-17% of SOC in all treatments. Results indicated that fire and its season of occurrence can significantly alter ecosystem processes and the storage of C and N in savanna ecosystems

Multi-objective calibration of RothC using measured carbon stocks and auxiliary data of a long-term experiment in Switzerland

Interactions between model parameters and low spatiotemporal resolution of available data mean that conventional soil organic carbon (SOC) models are often affected by equifinality, with consequent uncertainty in SOC forecasts. Estimation of belowground C inputs is another major source of uncertainty in SOC modelling. Models are usually calibrated on SOC stocks and fluxes from long‐term experiments (LTEs), whereas other point data are not used for constraining the model parameters. We used data from an agricultural long‐term (> 65 years) fertilization experiment to test a multi‐objective parameter estimation approach on the RothC model, combining SOC data from different fertilization treatments with microbial biomass, basal respiration and Zimmermann’s fractions data. We also compared two methods to estimate the belowground C inputs: a conventional scaling of belowground biomass from crop harvest yield and an alternative approach based on constant belowground C for cereals measured experimentally in the field. The resulting posterior parameter distributions still suffered from some equifinality; the most stable C pool kinetic constants and composition of exogenous organic matter were the most sensitive parameters. The use of fixed belowground C inputs for cereals improved the model performance, reducing the importance of treatment‐specific parameters and processes. The introduction of microbial biomass and basal respiration data was effective for increasing determination of the calibration, but also suggested a change in the model structure: the microbial biomass pool, which is proportional to the C inputs in the traditional models, could be represented by different microbial physiology functions

Physical and chemical protection of soil organic carbon in three agricultural soils with different contents of calcium carbonate

The amount of organic carbon physically protected by entrapment within aggregates and through polyvalent cation-organic matter bridging was determined on non-calcareous and calcareous soils. The composition of organic carbon in whole soils an

Nature of organic carbon and nitrogen in physically protected organic matter of some Australian soils as revealed by solid-state 13C and 15N NMR spectroscopy

The <53-□m particle-size fractions of 5 different Australian soils were subjected to high energy ultraviolet (UV) photo-oxidation for a period of 2 h in order to remove most of the physically unprotected organic material. Solid-state 13C and 15N nuclear magnetic resonance (NMR) spectroscopy was applied for characterising the chemical nature of the remaining organic fraction. The 13C NMR spectroscopic comparison of the residues after UV photo-oxidation and the untreated bulk soils revealed a considerable increase in condensed aromatic structures in the residues for 4 of the 5 soils. This behaviour was recently shown to be typical for char-containing soils. In the sample where no char was detectable by NMR spectroscopy, the physically protected carbon consisted of functional groups similar to those observed for the organic matter of the bulk sample, although their relative proportions were altered. The solid-state 15N NMR spectrum from this sample revealed that some peptide structures were able to resist UV photo-oxidation, probably physically protected within the core of microaggregates. Heterocyclic aromatic nitrogen was not detected in this spectrum, but pyrrolic nitrogen was found to comprise a major fraction of the residues after photo-oxidation of the <53-□m fractions of the char- containing soils. Acid hydrolysis of these samples confirmed that some peptide-like material was still present. The identification of a considerable amount of aromatic carbon and nitrogen, assignable to charred material in 4 of the 5 investigated soils, supports previous observations that char largely comprises the inert or passive organic matter pool of many Australian soils. The influence of such material on the carbon and nitrogen dynamics in such soils, however, requires further research.Peer reviewe

Types and chemical composition of organic matter in reforested lignite-rich mine soils

20 pages, 4 figures, 6 tables, 49 references.In the post-mining landscapes of Lusatia, forest soils develop from extremely aeid, lignite-rich open cast mine spoils. The sites have been ameliorated with 8sb from lignite-fired power stations prior to afforestation. During stand development, incorporation of plant-derived organic matter leads to an intimate mixture with the substrate-derived lignite in the first centimetres of the soil CAí horizon). The objective of the study was to characterise and to compare the composition of organic matter of mine soils under forest which contain substantial amounts of lignite. Therefore, the forest floor and the mineral soil (Ai and Cv horizon) under a 20-year-old pine and a 36-year-old red oak site were analysed for elemental composition, magnetic susceptibility, chemical structure by cross-polarisation magic angle spinning (CPMAS) I3C and ISN nuclear magnetic resonance (NMR) spectroscopy and lignite content by radiocarbon dating. The 13e CPMAS NMR spectra of!he forest fioor and Ai horizon reveal signals at 56, 72, 105, 119, 130 and 150 ppm, indicating the presence of carbohydrates and lignin ariginating from plant material. Additionally, structures characteristic for lignite material (aromatic and aliphatic carbon) could be observed in the Oh and Ai horizons. Using radiocarbon dating, 25 to 83% of the total carbon in these horizons can be assigned to lignite. Lignite carban may also indicate carbonaceous particles derived from amelioration ash as well as from lignite-derived airborne contamination, which are possible carbon sources of the forest floor and the surface soil. 13C NMR and radiocarbon dating show that the subsoil Cv horizon. is dominated by carbon derived from lignite. From these results it is concluded that mine soils, rich in lignite contain up to four organic matter types, namely lignite inherent to the parent substrate, organic matter derived from decomposition of plant residues, carbonaceous particles in amelioration ash and carbonaceous particles from airborne lignite-derived contamination. 15N NMR spectroscopy revealed that most of the nitrogen of these soils is of recent biogenic origin.Peer reviewe

Origin and composition of organic matter in pits from the Neolithic settlement at Murr, Bavaria

10 pages, 6 figures, 2 tables, 35 references.-- Como conferencia fue presentada en International Conference on soils and Archaeology 2: 47-49 (2003).-- International conference on soils and archaeology 2nd, International conference on soils and archaeology, Felici, Pisa, Italia.[EN]: The archaeological site in Murr, Upper Bavaria, was settled over the whole Neolithic period between 5500 and 2700 BC. Various pits and a ditch were found in the area, distinct from the surrounding loamy soil by the dark-brown colour of their filling materials. Although numerous artefacts were found, at the present stage of research neither the nature of the filling material nor the function of pits and ditches are well understood. Thus, the organic matter composition of 30 filling layers from 11 Neolithic pits of this settlement was investigated and compared to that of a close-by Luvisol profile and two A horizons from contemporary Phaeozems in southern Germany. The samples were subjected to C and N analysis, soil colour measurements, solid-state 13C CP MAS nuclear magnetic resonance (NMR) spectroscopy, combined fractionation/highenergy ultraviolet (UV) photo-oxidation/13C CPMAS NMR spectroscopy, polysaccharide and lignin analysis. The organic carbon contents are higher in the Neolithic samples than in the Luvisol horizons, but are generally lower than in the A horizons of contemporary phaeozemic soils developed from loess. The Neolithic samples show much higher colour intensity in darkness than the surrounding Luvisol horizons. The organic carbon content of the Neolithic samples can be correlated with the colour lightness value. Solid-state 13C NMR measurements revealed that this correlation is mostly due to their aromatic carbon content, which is considerably higher in the Neolithic samples compared to the contemporary soils. Low polysaccharide contents and no lignin-derived phenols are found in the Neolithic samples. Between 29 and 77% of soil organic carbon survived UV photo-oxidation, mostly present as aromatic structures. Dipolar dephasing NMR spectroscopy indicated a high degree of condensation for the aromatic rings, while scanning electron microscopy showed that the material had a plant-like morphology. Summarizing, the organic material filling the Neolithic pits shows significant differences in the overall chemical composition compared to the surrounding soil. It represents a highly altered, highly aromatic material, with no evidence for lignindegradation products, probably deriving from non-soil origin. There is strong evidence that the aromatic carbon is derived from charcoal. The material either originated from soil material that has undergone vegetation fires or from other charred organic material, e.g. residues from cooking or Neolithic fire places.[IT]: Origine e composizione della materia organica proveniente da pozzetti dell’insediamento neolitico di Murr, Baviera. Il sito archeologico di Murr (Baviera superiore), è stato abitato per tutto il Neolitico, tra 5500 e 2700 a.C. Nell’area sono stati rinvenuti numerosi pozzetti ed un fossato, distinguibili dal circostante suolo limoso per il colore bruno scuro del riempimento. Quantunque siano stati rinvenuti numerosi reperti, allo stato attuale delle ricerche né la natura del riempimento né la funzione dei pozzetti e del fossato sono ancora state comprese. Pertanto, la composizione della materia organica di 30 strati di riempimento di 11 pozzetti di questo insediamento è stata analizzata e confrontata con quella di un vicino Luvisol e due orizzonti A di Phaeozems della stessa età della Germania meridionale. Sui campioni sono state effettuate analisi di C ed N, misurazioni del colore, spettroscopia a stato solido CP MAS NMR del 13C, frazionamento/foto-ossidazione UV ad alta energia/spettroscopia 13C CP MAS NMR combinati, analisi dei polisaccaridi e della lignina. Il contenuto in C organico nei campioni neolitici è maggiore che negli orizzonti dei Luvisol, ma in genere minore che negli orizzonti A dei contemporanei Phaeozem sviluppati su loess. I campioni neolitici mostrano una maggiore intensità dei colori scuri rispetto a quella dei vicini Luvisol. Il contenuto in C organico dei campioni neolitici è correlato al colore, e le misure NMR a stato solido di 13C indicano che questa correlazione è dovuta soprattutto al loro contenuto in C aromatico, che è notevolmente superiore rispetto a quello dei suoli contemporanei. Nei campioni neolitici il contenuto in polisaccaridi è basso e non vi sono fenoli derivati dalla lignina. Da 29 a 77% del carbonio organico dei suoli ha resistito all’ossidazione UV, soprattutto come strutture aromatiche. La spettroscopia NMR a sfasamento dipolare ha posto in evidenza un forte grado di condensazione degli anelli aromatici, mentre la microscopia SEM ha mostrato morfologie vegetali. Riassumendo, il riempimento organico dei pozzetti neolitici mostra differenze significative nella composizione chimica generale rispetto ai circostanti suoli. È costituito da materiale fortemente aromatico molto alterato e senza prodotti di degrado della lignina, di origine probabilmente estranea al suolo. Vi sono forti indizi che il C aromatico derivi da carbone che ebbe origine da materiale pedogenetico coinvolto in incendi di vegetazione oppure da altro materiale organico carbonizzato, ad esempio residui di cottura o focolari neolitici.This work was supported by the DFG (Deutsche Forschungsgemeinschaft, Ko 1035/8-1).Peer reviewe

Comparison of structural stability, carbon fractions and chemistry of krasnozem soils from adjacent forest and pasture areas in south-western Victoria

Basalt-derived krasnozems are generally well-structured soils; however, there is a concern that intensive agricultural practices may result in an adverse decline in soil organic carbon, organic matter chemistry, and structural quality over time. A study was conducted on loam to silty clay loam krasnozems (Ferrosols) near Ballarat in south-western Victoria to assess changes in soil C, soil structural stability, and C chemistry, at the 0-10 cm soil depth, under 3 paired sites consisting of adjacent long-term forest (Monterey pine or eucalyptus) v. 30 year cropping [3 year pasture-2 year crops (potato and a root crop or grain)]. Soil structural stability was also characterised in the A and B horizons under long-term eucalyptus and several cropped sites. Organic C levels in the A horizons for all the soils were relatively high, ranging from 46 to 89 g/kg. A lower organic C (30%), associated mainly with loss of the sand-sized (> 53 mum) macro-C fraction, and a decrease in exchangeable Ca and Mg was found in the agricultural soils, compared with forest soils. Physically protected C in the <53 μm fraction, as indicated by UV photo-oxidation, was similar among soils. Wet sieving indicated a decline of both C and N concentration in water-stable aggregates and the degree of macro-aggregation under agricultural soils, compared with the forest soils. However, soil structural changes under cropping were mainly related to a decline in the >5 mm sized aggregates, with no deleterious increase in the proportion of 0.10 mm aggregates. Solid state C-13 NMR spectroscopy indicated a decrease in O-alkyl and alkyl C under pasture and cropping compared with forest soils, which was in agreement with the decline in the macro-C fraction. Characterisation of C chemistry following UV photo-oxidation showed that charcoal C (dominant presence of aryl C) accounted for 30% of the total soil organic C, while other functional groups (polysaccharides and alkyl C) were probably protected within micro-aggregates. Based on soil organic C and aggregate stability determinations alone, the implications for soil physical quality, soil loss, and diffuse pollution appear minimal