Assoziation organischer Bodensubstanz mit mineralischen Oberflächen in einem ackerbaulich genutzten Oberboden mit unterschiedlicher Bodentextur

Die Menge und mikroskalige Verteilung mineralassoziierter organischer Bodensubstanz (engl. mineral-associated organic matter, MOM) hängt von der Verfügbarkeit und Zugänglichkeit adsorptiver Mineraloberflächen ab. In tonarmen Böden mit wenig Mineraloberfläche müsste der Bedeckungsgrad an organischer Substanz entsprechend höher sein als in tonreichen Böden bei gleicher MOM Konzentration. In dieser Arbeit wurde MOM im Oberboden (0-20 cm) einer ackerbaulich genutzten (Para-)Braunerde mit unterschiedlicher Bodentextur untersucht. Die beprobte Fläche in Scheyern (Bayern, Deutschland) wurde einheitlich bewirtschaftet und mit gleichen Mengen organischen Materials versorgt. Der Texturgradient (6-37 % Partikel in der Tonfraktion) lässt sich wahrscheinlich auf unterschiedliche Lössanteile in den grobkörnigeren Tertiärsedimenten zurückführen. Um die MOM zu untersuchen, wurde aus der schweren Dichtefraktion >1,6 g cm‑3 die Feinschluff- (2‑6,3 µm) und Tonfraktion (0,2‑2 µm) gewonnen. Neben der Konzentration mineralassoziierten Kohlenstoffs wurde die chemische Zusammensetzung der MOM durch 13C-Festkörper-Kernresonanzspektroskopie bestimmt. In der Tonfraktion wurde durch Nano Sekundärionen-Massenspektrometrie (NanoSIMS) die räumliche Verteilung der Ionen 16O‑, 12C‑ und 12C14N‑ bestimmt, welche mittels Bildbearbeitung als Indikator des räumlichen organischen Bedeckungsgrads herangezogen wurde. Röntgenbeugungsanalysen haben gezeigt, dass die mineralogische Zusammensetzung ähnlich ist, wobei die Auswirkungen eines schwankenden Vermiculitgehalts noch durch Bestimmung der Kationenaustauschkapazität näher überprüft werden. Die Konzentration mineralassoziierten Kohlenstoffs in der Feinschluff und Tonfraktion war bei 6 % Tongehalt mit 80 mg g‑1 höher als bei 15 % Tongehalt mit 40 mg g‑1. In den Böden mit Tongehalt zwischen 15 und 30 % war die Konzentration mineralassoziierten Kohlenstoffs dagegen konstant bei etwa 40 mg g‑1. Zusätzlich zeigten die NanoSIMS-Messungen einen höheren organischen Bedeckungsgrad in den tonarmen Böden als in den tonreichen Böden. Unsere Daten besagen, dass in den untersuchten tonarmen Böden unter 15 % Tongehalt die MOM Konzentration als auch der Bedeckungsgrad höher ist je niedriger der Tongehalt. In den untersuchten tonreichen Böden über 15 % Tongehalt war die MOM Konzentration und der organische Bedeckungsgrad konstant niedrig, was auf ausreichende Verfügbarkeit und Zugänglichkeit adsorptiver Mineraloberflächen ab dieser Bodentextur schließen lässt

Projected loss of soil organic carbon in temperate agricultural soils in the 21^stcentury: effects of climate change and carbon input trends

Climate change and stagnating crop yields may cause a decline of SOC stocks in agricultural soils leading to considerable CO2 emissions and reduced agricultural productivity. Regional model-based SOC projections are needed to evaluate these potential risks. In this study, we simulated the future SOC development in cropland and grassland soils of Bavaria in the 21st century. Soils from 51 study sites representing the most important soil classes of Central Europe were fractionated and derived SOC pools were used to initialize the RothC soil carbon model. For each site, long-term C inputs were determined using the C allocation method. Model runs were performed for three different C input scenarios as a realistic range of projected yield development. Our modelling approach revealed substantial SOC decreases of 11–16% under an expected mean temperature increase of 3.3 °C assuming unchanged C inputs. For the scenario of 20% reduced C inputs, agricultural SOC stocks are projected to decline by 19–24%. Remarkably, even the optimistic scenario of 20% increased C inputs led to SOC decreases of 3–8%. Projected SOC changes largely differed among investigated soil classes. Our results indicated that C inputs have to increase by 29% to maintain present SOC stocks in agricultural soils

Forest soil organic matter: structure and formation

Soil organic matter represents a major component of the world surface carbon reserves. The total carbon in dead organic matter in the forest floor and in the underlying mineral soil has been estimated to be 1450 x 10"9t C, exceeding the amount stored in living vegetation by a factor of two or three (Schlesinger 1977; Meentemeyer et al., 1982; Jenkinson, 1988). Mineralization and humification represent important processes in the terrestrial carbon cycle. Schlesinger (1990) estimated that about 0.7% of the annual terrestrial net primary production is sequestered in refractory humic substances carbon. Organic matter of forest soils is composed of a mixture of above- and belowground plant residues (primary resources), microbial residues (secondary resources), and humic compounds (Swift et al., 1979). Humic compounds are formed concomitantly during the microbial decomposition of primary and secondary resources. The conceptual view of soil organic matter in the present study is that of a continuum ranging from fresh plant litter to humic substances, the final products of humification. A complete separation of plant remains and humic compounds is not possible, due to the fact that organic matter at all stages of degradation and humification is present simultaneously in natural soils, albeit at different amounts. The way in which the objective of this research will be addressed is the study of the chemical structural changes during humification of major plant components, namely lignin and aliphatic biomacromolecules. This is achieved by the analysis of bulk samples in comparison with different fractions. The fractionation procedure is chosen according to the suitability for the compound class under investigation. The data obtained in this way reveal that previous hypotheses on the humification processes in soils are unrealistic. In a final step the results obtained on the structural chemical trends of the individual components are combined with evidence from the literature and a hypothesis is proposed for the major humification processes in forest soils. (orig.)SIGLEAvailable from TIB Hannover: RO 9287(24) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Mechanisch-biologische Behandlung von zu deponierenden Abfaellen. Teilvorhaben 3/2: Humifizierungsprozesse und Huminstoffhaushalt waehrend der Rotte und Deponierung von Restmuell Abschlussbericht

SIGLEAvailable from TIB Hannover: F00B1147 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Neue Techniken zur Kompostierung. Teilvorhaben 13: Humifizierungsprozesse von Kompost nach der Ausbringung auf den Boden Endbericht

SIGLEAvailable from TIB Hannover: F98B1462 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

The modeling of reactive solute transport with sorption to mobile and immobile sorbents

This paper presents a mathematical model to describe the transport of reactive solutes with sorption to mobile and immobile sorbents. The mobile sorbent is considered to be reactive, too. The sorption processes mentioned are equilibrium and nonequilibrium processes. A transformation of the model in terms of total concentrations of solute and mobile sorbents is presented which simplifies the mathematical formulation. Effective isotherms, which describe the sorption to the immobile sorbent in the presence of a mobile sorbent and rate functions are introduced and their properties are discussed. The differences to existing approaches to model reactive solute transport are shown. Possible extensions are pointed out and the numerical approximation is sketched. The restrictions of the model as a consequence of the assumptions made on reactive solute transport are not due to mathematical reasons, but due to limitations of experimental information available. (orig.)Available from TIB Hannover: RR 5549(24)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Increased methane uptake but unchanged nitrous oxide flux in montane grasslands under simulated climate change conditions

Montane grasslands of Central Europe are expected to be exposed to strong warming and to altered precipitation patterns, suggesting that biosphere-atmosphere-hydrosphere exchange of carbon (C) and nitrogen (N) compounds may be vulnerable to future climatic conditions. By transferring small lysimeters along an altitudinal gradient, we assessed the impact of climate change conditions on soil-atmosphere exchange of methane (CH4) and nitrous oxide (N2O) as well as on ammonium (NH4+) and nitrate (NO3-) in soil water in extensively managed montane grassland in southern Germany. Lysimeter transfer to lower altitude increased air and soil temperatures by more than 2 degrees C and reduced summer precipitation as well as soil moisture throughout the year compared with a control transfer within the high altitude site. This simulation of climate change conditions almost doubled the CH4 sink strength from -0.11 to -0.19gCm(-2)year(-1), which appeared to be mainly related to improved gas diffusion after reduced soil moisture. Mean NH4+ and NO3- concentrations in soil water (0.05mg NH4+-Nl(-1) and 0.08mg NO3--Nl(-1)) and N2O emissions (approximately 0.03gNm(-2)year(-1)) remained small and unaffected by climate change simulation. Our study suggests that expected climate change conditions will have positive effects on the non-CO2 greenhouse gas balance in extensively managed montane grassland because of increased net CH4 uptake in soil. For N2O emission, we conclude that potential effects of management changes may override the small effects of simulated climate change on N2O emissions observed in this study

Tree girdling provides insight on the role of labile carbon in nitrogen partitioning between soil microorganisms and adult European beech.

Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitriflers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined. Surprisingly plants preferred organic N over inorganic N and nitrate (NO3-) over ammonium (NH4+) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi Cenococcum geophilum was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of C. geophilum remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms

N balance and cycling of Inner Mongolia typical steppe: a comprehensive case study of grazing effects

Increasing grazing pressure and climate change affect nitrogen (N) dynamics of grassland ecosystems in the Eurasian steppe belt with unclear consequences for future delivery of essential services such as forage production, C sequestration, and diversity conservation. The identification of key processes responsive to grazing is crucial to optimize grassland management. In this comprehensive case study of a Chinese typical steppe, we present an in-depth analysis of grazing effects on N dynamics, including the balance of N gains and losses, and N cycling. N pools and fluxes were simultaneously quantified on three grassland sites of different long-term grazing intensities. Dust deposition, wind erosion, and wet deposition were the predominant but most variable processes contributing to N losses and gains. Heavy grazing increased the risk of N losses by wind erosion. Hay-making and sheep excrement export to folds during nighttime keeping were important pathways of N losses from grassland sites. Compared to these fluxes, gaseous N losses (N2O, NO, N-2,N- and NH3) and N losses via export of sheep live mass and wool were of minor relevance. Our N balance calculation indicated mean annual net N losses of 0.9 +/- 0.8 g N/m(2) (mean +/- SD) at the heavily grazed site, whereas the long-term ungrazed site was an N sink receiving mean annual inputs of 1.8 +/- 1.1 g N/m(2), mainly due to dust deposition. Heavy grazing reduced pool sizes of topsoil organic N, above- and belowground biomass, and N fluxes with regard to plant N uptake, decomposition, gross microbial N turnover, and immobilization. Most N-related processes were more intensive in seasons of higher water availability, indicating complex interactions between land use intensity and climate variability. The projected increase of atmospheric N depositions and changes in rainfall pattern imposed by land use change will likely affect N sink-source pathways and N flux dynamics, indicating high potential impact on grassland ecosystem functions. Land use practices will be increasingly important for the management of N dynamics in Chinese typical steppe and, therefore, must be considered as key component to maintain, restore or optimize ecosystem services