No depth-dependence of fine root litter decomposition in temperate beech forest soils

Aims Subsoil organic carbon (OC) tends to be older and is presumed to be more stable than topsoil OC, but the reasons for this are not yet resolved. One hypothesis is that decomposition rates decrease with increasing soil depth. We tested whether decomposition rates of beech fine root litter varied with depth for a range of soils using a litterbag experiment in German beech forest plots. Methods In three study regions (Schorfheide-Chorin, Hainich-Dün and Schwäbische-Alb), we buried 432 litterbags containing 0.5 g of standardized beech root material (fine roots with a similar chemical composition collected from 2 year old Fagus sylvatica L. saplings, root diameter<2mm) at three different soil depths (5, 20 and 35 cm). The decomposition rates as well as the changes in the carbon (C) and nitrogen (N) concentrations of the decomposing fine root litter were determined at a 6 months interval during a 2 years field experiment. Results The amount of root litter remaining after 2 years of field incubation differed between the study regions (76 ± 2 % in Schorfheide-Chorin, 85 ± 2 % in Schwäbische-Alb, and 88±2 % in Hainich-Dün) but did not vary with soil depth. Conclusions Our results indicate that the initial fine root decomposition rates are more influenced by regional scale differences in environmental conditions including climate and soil parent material, than by changes in microbial activities with soil depth. Moreover, they suggest that a similar potential to decompose new resources in the form of root litter exists in both surface and deep soils

Determination of trace amounts of nitrate in potassium chloride-extracts by HPLC with ultra-violet-detection

A method is presented that allows the determination of trace amounts of nitrate in I M potassium chloride extracts of environmental soil samples from Northern Europe. To avoid the interference of bromine ions on the evaluation of the nitrate peak, 50 muL of a 50mg/L nitrate standard solution are added to a 5mL soil extract. This makes sure that the overall nitrate concentration in the spike is >500 mug/L which allows an exact and reliable determination of the nitrate concentration. Analyses of the soil extracts are carried out by anion-exchange HPLC with ultra-violet detection at lambda = 210nm using 0.1 M KCl as eluent. Concentrations down to 25 mug/L of nitrate can be analyzed

Long-term monitoring of arsenic and selenium species in contaminated groundwaters by HPLC and HG-AAS

The long-term concentration and distribution of species of arsenic and selenium in contaminated groundwaters from Kelheim was monitored. Most of the groundwater wells contained elevated concentrations of iron, manganese and sulfur, Arsenic (III), arsenic (V), selenium (IV) and selenium (VI) were separated using high performance liquid chromatography (HPLC) based on phosphate buffers and collected in fractions. Due to the complex matrix, the fractions were analyzed element-specifically by hydride-generating atomic absorption spectrometry (HG-AAS). The combination of HPLC and HG-AAS was selected due to the authors' intention of developing an easy-to-handle, but nonetheless reliable, method suitable for the long-term monitoring of species distribution in an almost routine way? and taking account of the threshold values of 10 mu g/l for each element, indicated by German drinking water regulations. To enhance the reliability of the method, analytical quality control experiments were carried out. When applied to groundwater wells from Kelheim (Germany) they revealed that arsenic (V) and selenium (VI) were the dominating species, The presence of arsenic (III) and selenium (IV) was assumed to be supported by organic matter. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 15

The capability of ultrafiltration and ETV-ICP-MS for size fractionation studies of arsenic and selenium species in ground water samples with high concentrations of iron, manganese and sulfur

A simple, but highly sensitive procedure for the determination of particular and colloidally bound arsenic and selenium species in ground water samples with high concentrations of iron, manganese and sulfur is presented. Samples were first filtered through a 0.45 mu m filter to separate the particulate matter from the dissolved. Aliquots of the filtered sample were submitted to ultrafiltration through membrane filters with pore diameters of 30 nm and 1 nm, respectively. Filtrates were analyzed by ETV-ICP-MS for their arsenic and selenium concentration. [References: 20

Secreted pitfall-trap fluid of carnivorous Nepenthes plants is unsuitable for microbial growth

Background and Aims Carnivorous plants of the genus Nepenthes possess modified leaves that form pitfall traps in order to capture prey, mainly arthropods, to make additional nutrients available for the plant. These pitchers contain a digestive fluid due to the presence of hydrolytic enzymes. In this study, the composition of the digestive fluid was further analysed with regard to mineral nutrients and low molecular-weight compounds. A potential contribution of microbes to the composition of pitcher fluid was investigated