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Dissolved components in precipitation water percolated through forest litter (2000)

Hongve, D. ; Van Hees, P. A. W. ; Lundström, U. S.

Oxford, UK : Blackwell Science Ltd

European journal of soil science 51 (2000), S. 0

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ISSN: 1365-2389

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Leaves lying on the forest floor are a major source of dissolved organic substances in soil and surface waters, and these substances have important effects in those environments. We used zero-tension lysimeters to study the chemical characteristics of water percolating through litter from various species of forest trees. The leaching rates were greatest in the autumn and declined rapidly thereafter, especially for deciduous litter. During an annual cycle, 2.5–17% of the initial contents of the carbon in the litter was recovered as dissolved organic carbon in percolates. Humus-like substances, hydrophilic acids and hydrophilic neutral compounds constituted the major fractions of dissolved C. Leachates from deciduous leaf litter were only partly biodegradable, and those from spruce needles were scarcely biodegradable.Low molecular weight organic acids constituted 0–12% of the dissolved organic carbon in the percolates of the first autumn sampling and decreased over time. Acetic and formic acids were present at the largest concentrations, up to 30 μmol l−1 per g litter, and gluconic, pyruvic, fumaric, oxalic and citric acids were also frequent in significant concentrations. Among the aromatic acids, p-hydroxybenzoic acid was identified in four out of five autumn samples. The organic components in litter leachates are important for the microbial activity in soil and surface waters. The organic acids enhance weathering and translocation of metals by their ability to form complexes. Litter is also a source of inorganic ions in soil solutions. The dominant cations in the percolates were K+, Ca2+ and Mg2+, and spruce litter also yielded large quantities of Al and Fe.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2389.2000.00339.x

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Mobilization of aluminium, iron and silicon by Picea abies and ectomycorrhizas in a forest soil (2004)

Van Hees, P. A. W. ; Jones, D. L. ; Jentschke, G. ; [et al.]

Oxford, UK : Blackwell Science Ltd

European journal of soil science 55 (2004), S. 0

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ISSN: 1365-2389

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Weathering of soil minerals is a key determinant of ground and surface water quality and is also important in pedogenic and rhizosphere processes. The relative importance of biotic and abiotic studies in mineral weathering, however, is poorly understood. We investigated the impact of Picea abies seedlings, an ectomycorrhizal fungus and humic acid on the solubilization of aluminium (Al), iron (Fe) and silicon (Si) in an E horizon forest soil over 10 months. Elemental budgets were constructed based upon losses in drainage water, accumulation in plants and changes in the pools of exchangeable ions. Plants and mycorrhizas or both had a significant effect on the total amounts of Al, Fe and Si mobilized from the soil. Significantly larger amounts of Al and Fe were recovered in plants than those lost in drainage water, whereas the opposite trend was true for Si. The continual addition of dissolved organic matter to the soil in the form of humic acid had an effect only on mobilization of Fe, which increased due to larger plant uptake and an increase in the exchangeable pool. The mobilization of Fe and Si were positively correlated with hyphal length, soil respiration and concentrations of oxalate in the soil solution, and mobilization of Al was strongly correlated with plant weight. Scanning electron microscopy revealed that most fungal hyphae were associated with mineral surfaces with little occupation of cracks and micropores within mineral grains. Evidently ectomycorrhizas have important impacts on mineral dissolution and the chemistry of forest soils.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2389.2003.00581.x

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Impact of ectomycorrhizas on the concentration and biodegradation of simple organic acids in a forest soil (2003)

Van Hees, P. A. W. ; Godbold, D. L. ; Jentschke, G. ; [et al.]

Oxford, UK : Blackwell Science Ltd

European journal of soil science 54 (2003), S. 0

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ISSN: 1365-2389

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Simple organic acids seem to be important in many soil processes including nutrient uptake in the rhizosphere and long-term pedogenic processes such as podzolization. The factors regulating the concentrations of these acids in soil, however, remain poorly understood. We have investigated one set of factors, namely the impact of ectomycorrhizal (Paxillus involutus) and non-mycorrhizal Picea abies seedlings and humic acid on the concentration and dynamics of organic acids in soil solution. We did so over 10 months in laboratory columns containing soil from the E horizon of a sandy forest soil. Several organic acids were identified in the solution extracted from the root zone including oxalic, citric, malonic, succinic, acetic, formic and lactic acids at concentrations ranging from 〈0.1 to 2.3 µm. Both plants and ectomycorrhizas had significant effects on the concentration of organic acids in soil solution. In contrast, omitting P from the irrigation water appeared to have little effect on the concentrations. The microbial mineralization kinetics of oxalate conformed well to a single Michaelis–Menten equation. Further, the soil with the mycorrhizas had a significantly faster mineralization of oxalic acid over a wide concentration range than did the soil without ectomycorrhizas and without plants. We conclude that the oxalate flux through the soil with both trees and mycorrhizas is much faster than is evident from measurements of solution concentration at steady state. Humic acid had little effect on the concentrations of organic acids or dynamics in the soil solution. Oxalic acid concentrations in the soil solution were correlated with hyphal length, rate of microbial mineralization, soil respiration, and shoot to root weight ratio. We conclude that both mycorrhizas and plants have a large impact on organic acid cycling in forest soils.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1351-0754.2003.0561.x

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4

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Rock-eating fungi (1997)

Jongmans, A. G. ; van Breemen, N. ; Lundström, U. ; [et al.]

[s.l.] : Macmillan Magazines Ltd.

Nature 389 (1997), S. 682-683

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Weatherable minerals under many European coniferous forests contain a network of numerous tubular pores, formed by organic acids exuded by fungi. We believe that symbiotic mycorrhizal hyphae translocate dissolved minerals from the isolated micropores directly to their host plants, bypassing ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/39493

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Combustion behaviour of fabric and polyurethane flexible foam mock-up combinations under Cone Calorimetry test conditions (1993)

Vanspeybroeck, R. ; Van Hees, P. ; Vandevelde, P.

New York, NY [u.a.] : Wiley-Blackwell

Fire and Materials 17 (1993), S. 167-172

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ISSN: 0308-0501

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: The relative contributions of fabric and foam on important fire hazard parameters as measured in the cone calorimeter were determined for various mock-up combinations. Three commercial types of high-resilience PU flexible slabstock foams, representing a wide range of combustion performance, were combined with three different fabrics: polyester, polypropylene and combustion-modified cotton. Total heat release of the combinations correspond well with the value calculated from the individual components and is determined by the density and effective heat of combustion of the components, and the foam/fabric weight ratio. The foams show a smaller variation in effective heat of combustion than the fabrics. Covering of PU flexible foams with a fabric results in general in a delay of ignition and peak rate of heat release. Performance of the mock-ups is mainly determined by the fabric but is also influenced by the quality of the foam.

Additional Material: 8 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/fam.810170404

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Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions (1993)

Vanspeybroeck, R. ; Van Hees, P. ; Vandevelde, P.

New York, NY [u.a.] : Wiley-Blackwell

Fire and Materials 17 (1993), S. 155-166

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ISSN: 0308-0501

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: The first part of this study focuses on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) moulded foams. A decrease in heat flux (down to 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 25 mm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW m-2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large differences in combustion performance in small-scale flammability tests performed almost identically in the cone calorimeter. In the second part of this study the effects of foam variables, such as foam type, density and melamine content, are defined. These effects were clearly pronounced at radiant flux levels of 15-25 kWm-2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion in HR-slabstock and all MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.

Additional Material: 18 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/fam.810170403

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