Bernd Marschner

Controls of bioavailability and biodegradability of dissolved organic matter in soils

Abstract In soils, dissolved organic matter (DOM) is probably the most bioavailable fraction of soil organic matter, since all microbial uptake mechanisms require a water environment. Bioavailability describes the potential of microorganisms to interact with DOM. It is a prerequisite for biodegradation and can be restricted, if DOM is present in small pores or within soil aggregates and therefore not accessible for microorganisms. DOM biodegradation is defined as the utilisation of organic compounds by soil microorganisms quantified by the disappearance of DOM or O2 or by the evolution of CO2. The controlling factors for DOM biodegradability can be divided into three groups, namely, intrinsic DOM quality parameters, soil and solution parameters and external factors. DOM characteristics that generally enhance its biodegradability are high contents of carbohydrates, organic acids and proteins for which the hydrophilic neutral fraction seems to be a good estimate. In contrast, aromatic and hydrophobic structures that can also be assessed by UV absorbance decrease DOM biodegradability, either due to their recalcitrance or due to inhibiting effects on enzyme activity. Effects of solution parameters such as Al, Fe, Ca and heavy metal concentrations on DOM biodegradability have been documented in various studies, however with different, sometimes conflicting results. Inhibitory effects of metals are generally attributed to toxicity of the organic complexes or the free metal ions. In contrast, the enhanced degradability observed in the presence of metal ions may be due to flocculation, as larger structures will provide better attachment for microbial colonies. As degradation is dependent on microbial activity, the composition and density of the microbial population used in the degradation studies also influence biodegradation. Site-specific factors, such as vegetation, land use and seasonality of meteorological parameters control DOM composition and soil and soil solution properties and therefore also affect its biodegradability. The major obstacle for a better understanding of the controls of DOM biodegradability is the lack of a standardised methodology or at least systematic comparisons between the large number of methods used to assess DOM biodegradability.

Priming effects of sugars, amino acids, organic acids and catechol on the mineralization of lignin and peat

The 14C-labeled substrates glucose, fructose, alanine, glycine, oxalic acid, acetic acid, and catechol were incubated at 20 °C in a model system that consisted of sand mixed with lignin or peat (3 % Corg). Each substrate was added at either 80 or 400 μg C (g sand)—1. During 26 days of incubation with an inoculum extracted from forest soil, the amount of CO2 evolved was measured hourly. The amount of 14CO2 was determined after 4, 6, 12, 19, and 26 days. After 26 days of incubation, each substrate showed priming effects, but not in all examined treatments. Most substrates stimulated the degradation of the model substances (positive priming effects). Negative priming effects only were found in the lignin system with oxalic acid and catechol addition at both concentrations. The strongest positive priming occurred in the peat system with the oxalic acid addition of 80 μg C g—1 where 1.8 % of the peat were mineralized after 26 days, compared to 0.7 % in the control. The addition of 400 μg alanine-C g—1 caused the strongest increase in lignin mineralization, amounting to 3.9 % compared to 2.8 % in the control. During the incubation the extent of priming changed with time. Most substrates caused the strongest effects during the first 4 to 10 days of incubation. The extent of priming depended on substrate type, substrate concentration, and organic model substance. Possibly this is due to the activation of different microorganisms. Priming-Effekte von Zuckern, Aminosauren, organischen Sauren und Brenzcatechin auf die Mineralisation von Lignin und Torf Die 14C-markierten Substrate Glucose, Fructose, Alanin, Glycin, Oxalsaure, Essigsaure und Brenzcatechin wurden bei 20�°C in einem Modell-System inkubiert, das aus mit Lignin oder Torf gemischtem Seesand bestand (3 % Corg). Jedes Substrat wurde in den Konzentrationen 80 oder 400 μg C (g Sand)—1 zugegeben. Wahrend einer 26-tagigen Inkubation mit Zugabe eines Inokulums aus einem Waldboden wurde die CO2-Entwicklung stundlich gemessen. Die Menge an 14CO2 wurde nach 4, 6, 12, 19 und 26 Tagen bestimmt. Nach 26-tagiger Inkubation konnten fur jedes Substrat Priming-Effekte nachgewiesen werden, jedoch nicht immer in allen untersuchten Varianten. Die meisten Substrate steigerten den Abbau der Modellsubstanzen (positive Priming-Effekte). Negative Priming-Effekte wurden nur im Lignin-System nach Zugabe von Oxalsaure und Brenzcatechin bei beiden Substratkonzentrationen beobachtet. Der starkste positive Priming-Effekt trat im Torf-System nach Zugabe von 80 μg Oxalsaure-C g—1 auf. Nach 26 Tagen waren 1,8 % des Torf mineralisiert im Vergleich zu 0,7 % in der Kontrolle. Bei Lignin hatte die Zugabe von 400 μg Alanin-C g—1 den starksten Effekt auf die Mineralisation. Anstelle von 2,8 % in der Kontrolle, wurden 3,9 % des Lignins mineralisiert. Wahrend der Inkubation anderte sich das Ausmas des Priming mit der Zeit. Die meisten Substrate verursachten die starksten Effekte innerhalb der ersten 4 bis 10 Tage. Das Ausmas des Priming-Effekts war abhangig von Substratart, -konzentration und der organischen Modellsubstanz. Dies ist moglicherweise auf die Aktivierung unterschiedlicher Mikroorganismen zuruckzufuhren.

The effect of liming on quantity and chemical composition of soil organic matter in a pine forest in Berlin, Germany

The study was carried out in a 40-yr old pine plantation on a Cambic Arenosol within the urban area of Berlin. Lime application (6.1 t ha-1) has led to a pH increase in the forest floor from 3.3 to 5.5 within one year and to a strong stimulation of macrofaunal and microbiological activity. Three years after liming, the C:N ratio of the forest floor decreased from 28 to 25 and P, Pb, Zn, Cu and Cd concentrations in organic matter increased significantly. The organic C pool of the forest floor was almost 7 t ha-1 lower in the limed plot which is attributed to increased microbial respiration. In the mineral soil too, C-pools are lower in the limed plot, amounting to 13.2 t ha-1 or 14% less than in the control. C:N ratios have narrowed significantly from 27–29 to 23 in 10–30 cm depth. The humic acid fraction is lower throughout the limed profile while the percentage of fulvic acids has increased significantly below 10 cm. The results point to severe losses of organic matter and to profound changes in its composition. This may be of consequences for site quality and leaching processes.

Chemical and biological processes leading to the neutralisation of acidity in soil incubated with litter materials

Plant materials containing high amounts of ash alkalinity can be utilized to increase the pH of acid soils but the chemical and biological processes involved in the release of this alkalinity are not fully understood. In this laboratory study fresh leaf litter from two tree species (Melia azedarach, Castanea sativa) and sugarcane (Saccharum oAcinarum) trash containing ash alkalinities of 288, 141 and 33 mmolc kg ˇ1 respectively, were mixed at three diAerent rates (4, 16, 32 mg g ˇ1 ) with acidic topsoil from a Ultic Palexeralf and incubated at 90% WHC and at 258C for 20 d while monitoring CO2-evolution. Treatment eAects were assessed by measuring changes in pH, acid buAering curves and exchangeable cations before and after incubation. Furthermore, soluble organic compounds, mineral N-forms were determined in soil extracts. Immediately after mixing, up to 50% of the added alkalinity was available for acid neutralisation. After incubation, acid neutralisation capacity at pH 4 (ANCpH4) and the pH of the soils with the two higher amendment rates had increased in all treatments. The changes were most pronounced in the Melia amended soils, followed by Castanea and sugarcane and reflected the added amounts of ash alkalinity. In all treatments, soil respiration increased with amendment rate and was closely related to a decline in soluble organic carbon during incubation. Together with the shift from stronger to weaker acidity observed after incubation, this is evidence for the microbial decarboxylation of soluble organic anions. 7 2000 Elsevier Science Ltd. All rights reserved.

Effects of treated wastewater irrigation on the dissolved and soil organic carbon in Israeli soils.

In many arid and semi-arid regions, the demand for drinking water and other domestic uses is constantly growing due to demographic growth and increasing standard of living. Therefore, less freshwater is available for agricultural irrigation and new water sources are needed. Treated wastewater (TWW) already serves as an important water source in Israel since more than 40 years and its usage will further be extended. Related to its high loads with nutrients, salts and organic materials its use as irrigation water can have major effects on the soil physical, chemical and biological properties, in the worst case leading to soil degradation. Additional organic matter reaches the soil with the effluent water and soil microbial activity is stimulated. Soil organic carbon (SOC) seems to accumulate in the topsoil and tends to decrease after long-term irrigation with secondary TWW in the subsoil. The amount of dissolved organic carbon increased and the aromaticity of the organic compounds in the soil percolates decreased over the irrigation period. Priming effects, occurring after stimulation of microbial activity by the addition of easily degradable substances, could be found in the soils and were stronger for subsoil (1 m depth).

Sorption von polyzyklischen aromatischen Kohlenwasserstoffen (PAK) und polychlorierten Biphenylen (PCB) im Boden

Hydrophobe organische Umweltchemikalien wie die PAK und PCB sorbieren im Boden vornehmlich an die organische Substanz.Uber die Sorptionsmechanismen existieren verschiedene Modellvorstellungen, die von kovalenten Bindungen uber hydrophobe Wechselwirkungen bis diffusionsgesteuerten Verteilungsprozessen reichen. Durch die Sorption an geloste organische Substanzen (DOM) kann die Verteilung der hydrophoben Verbindungen zugunsten der Losungsphase verschoben sein, und es werden fur ein solches 3-Phasen System Modellrechnungen zur Abschatzung des DOM-Mobilisierungspotentials vorgestellt. Viele Untersuchungen zeigen weiterhin, das das Sorptionsvermogen der organischen Substanz von bestimmten Qualitatsparametern wie Aromatizitat und Molekulgrose abhangt und auch durch das chemische Milieu (pH, Salze) beeinflust werden kann. Trotz groser Fortschritte im Verstandnis dieser Zusammenhange bestehen aber noch eine Vielzahl von Forschungsdefiziten. Sorption of polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) in soil Hydrophobic organic compounds such as PAH and PCB in soils are mainly sorbed to organic matter. There exist several conceptual models about the sorption mechanisms which encompass covalent bonds, hydrophobic interactions and diffusion-controlled partitioning. The partitioning of hydrophobic compounds into the aqueous phase can be enhanced through sorption to dissolved organic matter (DOM). For such 3-phase systems, some model calculations are presented in order to evaluate the mobilizing potential of DOM. Many investigations show that the sorptivity of organic matter is influenced by certain quality parameters such as aromaticity and molecular size. In addition, it can be modified by the chemical environment (pH, salts). But despite the progress made in the last years in the understanding of these relationships there remains a multitude of open questions and further research needs.

Factors controlling the biodegradation of 17β-estradiol, estrone and 17α-ethinylestradiol in different natural soils

We conducted a series of laboratory microcosm incubations with [(14)C]-labeled 17beta-estradiol (E2), estrone (E1) and 17alpha-ethinylestradiol (EE2) in 17 different natural soils to characterize hormone mineralization. A significantly higher mineralization was observed for E1 (2.0-37.6%) and E2 (4.2-50.2%) than for EE2 (0.5-2.6%) in all test soils after 21 days. Soil physical or chemical parameters were not related to estrogen mineralization. Although sorption parameters varied greatly for E2 (K(F)=21.9-317.5 mL g(-1)), for E1 (K(F)=46.0-517.5 mL g(-1)) and for EE2 (K(F)=29.9-326.1 mL g(-1)) this apparently did not control estrogen bioavailability since it showed no effects on hormone mineralization. In order to elucidate the controlling factors, experiments with combined additions of radiolabeled estrogens and different substrates were conducted. Additions of ammonium nitrate or alanine to soil samples generally increased EE2 mineralization, thus indicating N-limitation. Additions of glucose induced higher E2 and EE2 degradation in comparison to control samples which is attributed to co-metabolism. Additions of saw dust, catechol or streptomycin influenced the microbial population in the test soils and affected the mineralization of E2 and EE2. Thus, we clearly demonstrate that different microbial communities are responsible for E2 and EE2 degradation in soils. We suggest that EE2 is mineralized by white-rot fungi and E2 by bacteria.

Dissolved organic carbon from sewage sludge and manure can affect estrogen sorption and mineralization in soils.

In this study, effects of sewage sludge and manure borne dissolved organic carbon (DOC) on 17beta-estradiol (E2) and 17alpha-ethinylestradiol (EE2) sorption and mineralization processes were investigated in three agricultural soils. Batch equilibrium techniques and equilibrium dialysis methods were used to determine sorption mechanisms between DOC, estrogens and the soil solid phase. It was found that that the presence of organic waste borne DOC decreased estrogen sorption in soils which seems to be controlled by DOC/estrogen complexes in solution and by exchange processes between organic waste derived and soil borne DOC. Incubation studies performed with (14)C-estrogens showed that DOC addition decreased estrogen mineralization, probably due to reduced bioavailability of estrogens associated with DOC. This increased persistence combined with higher mobility could increase the risk of estrogen transport to ground and surface waters.

Kinetics of the release of dissolved organic matter (DOM) from air-dried and pre-moistened soil material.

In this study, the kinetics of soil organic matter (SOM) dissolution from soil samples in different states of moisture was investigated, using a continuous extraction method. The investigation distinguished three processes of SOM dissolution. They include an initial, fast process (probably hydrophilic dissolved organic matter) and two slow, rate limited processes, which probably correspond to hydrophobic dissolved organic matter (DOM). The second process indicates a slow, continuous release of DOM, whereas the third process is determined by a power law. The rate of the third process strongly depends on temperature and state of moisture. It is diffusion limited, with the diffusion control probably being located in the solid soil organic matter. This was explained by a gel structure, which slowly forms in the hydrating SOM and allows diffusion of mobile particles of SOM. The results show the importance of considering the moisture state of SOM for the kinetics of DOM dissolution. Kinetik der Freisetzung geloster organischer Substanzen (DOM) aus luftgetrocknetem und vorbefeuchtetem Bodenmaterial In dieser Studie wurde mit Hilfe einer kontinuierlichen Extraktionsmethode die Kinetik der Freisetzung geloster organischer Substanzen (DOM) aus Bodenmaterial in unterschiedlichen Feuchtezustanden untersucht. Es konnten drei verschiedene Teilprozesse im Auflosungsvorgang unterschieden werden. Diese beinhalten einen anfanglich schnellen Vorgang (wahrscheinlich hydrophile DOM) und zwei kinetisch kontrollierte Vorgange, die wahrscheinlich der hydrophoben DOM zuzuordnen sind. Der zweite Vorgang weist auf eine langsame, kontinuierliche DOM-Freisetzung hin, wahrend der dritte Vorgang durch einen Potenzterm beschrieben werden kann. Die Geschwindigkeit des dritten Vorganges wird stark von der Temperatur und vom Feuchtezustand der Probe bestimmt. Er ist diffusionskontrolliert, wobei die Diffusionskontrolle wahrscheinlich in der festen organischen Bodensubstanz lokalisiert ist. Dies wurde mit einer Gelstruktur erklart, die sich langsam in der quellenden organischen Bodensubstanz ausbildet und eine Diffusion mobiler Partikel der organischen Bodensubstanz ermoglicht. Die Ergebnisse weisen auf die Bedeutung des Feuchtezustandes der organischen Bodensubstanz fur die Kinetik der DOM-Freisetzung hin.

Potential hazards of lime application in a damaged pine forest ecosystem in Berlin, Germany

Ninety percent of the pines (P. Sylvestris) in the forests of Berlin (West) are classified as damaged. Needle and leaf analyses do not indicate nutrient deficiencies. In site of high S-inputs (55 kg ha−1 yr−1 with throughfall) total acid inputs are moderate (2.4 kmol ha−1 yr−1) due to their neutralization by carbonatic dusts. Heavy metal depositions have led to accumulations in the forest floor (e.g. Pb 150 mg kg−1, Cd 0.5 mg kg−1). The dominating soil type, a cambic arenosol (Ustipsamment) is strongly acidified (pH 3.2 – 4.0) and poor in available nutrients. On an experimental plot, the application of dolomitic lime (6.1 tons ha−1) and fertilizer (145 kg ha−1 K2SO4) led to a significant increase m pH and base saturation in the top 10 cm of the mineral soil after 2 yr. The data on element fluxes give evidence for increased mineralization rates, enhanced heavy metal accumulation in the forest floor and increased soil solution concentrations of potentially hazardous substances (Al, Cd, NO3). The lime application is discussed in terms of site specific effects on ecosystem stability and groundwater quality.