André Schlichting

Sequentially extracted phosphorus fractions in peat‐derived soils

Phosphorus (P) forms were sequentially extracted from peat derived soils (Eutric Histosols and Gleysols) at eight sites in Saxony-Anhalt (Germany) to disclose general differences in P pools between mineral and organic soils and to investigate effects of peat humification and oxidation in conjunction with land use and soil management on the P status of soils. Overall 29 samples providing a wide variety of basic chemical properties were subjected to the Hedley fractionation. The Histosol topsoils contained more total P (P t ) (1345 ± 666 mg kg -1 ) than the Gleysol topsoils (648 ± 237 mg kg -1 ). The predominant extractable fractions were H 2 SO 4 -P (36-63 % of P t ) in calcareous and NaOH-P o (0-46 % of P t ) in non-calcareous Histosols. These soils had large pools of residual P (13-93 % of P t ). Larger contents and proportions of P o and of labile P fractions generally distinguished organic from mineral soils. Regression analyses indicated that poorly crystalline pedogenic oxides and organic matter were binding partners for extractable and non-extractable P. Intensive management that promotes peat humification and oxidation results in disproportional enrichments of labile P fractions (resin-P, NaHCO 3 -P i , and NaHCO 3 -P o ). These changes in P chemistry must be considered for a sustainable management of landscapes with Histosols and associated peat derived soils.

Effects of pretreatment on sequentially-extracted phosphorus fractions from peat soils

The composition and peculiarity of peat requires a critical evaluation of pretreatment for their effects on sequentially-extracted phosphorus (P) fractions. Therefore, these effects were determined on the sequential P fractionation scheme according to Hedley, which has been seldom applied to peat soils. A field-moist, low-moor peat was sampled and subjected to two drying and three storing techniques prior to the Hedley P fractionation. The P concentrations in nearly all fractions differed among treatments. The proportions of resin-P and NaHCO3-P decreased in the order fresh>frozen>cool stored. Drying led to great increases in the proportion of residual P, most of which was assigned to organic P forms. Organic P extracted by NaHCO3 and NaOH disappeared or was lowered in proportion due to drying. It was concluded that sequential P fractionation should be carried out with fresh peat samples to avoid undesired changes in the fractions.

New evidence for the molecular–chemical diversity of potato plant rhizodeposits obtained by pyrolysis–field Ionisation mass spectrometry

INTRODUCTION Detailed descriptions of the molecular-chemical diversity in plant rhizodeposits are scarce. The vast majority of our knowledge is derived from a priori methods of analysis, such as GC-MS and HPLC. OBJECTIVE To analyse the composition of rhizodeposits from the potato cultivar Solanum tuberosum L. cv. Albatros by pyrolysis -field ionisation mass spectrometry (Py-FIMS) and to explain differences in relation to plant growth stage and photoperiod. METHODOLOGY Potato (Solanum tuberosum L.) plants were grown in non-sterile, native soil under controlled environmental conditions (plant chamber). Rhizodeposit samples were collected by leaching during two different growth stages and after the physiological day- and night-cycle. All leachate samples were investigated by Py-FIMS. Mass spectrometric data were evaluated by multivariate statistics. RESULTS Screening of the rhizodeposits by Py-FIMS revealed a broad range of m/z signals. Low-molecular-weight substances of m/z 15-56 (8.1-18.6%), alkylaromatics (12.0-15.9%), phenols and lignin monomers (8.8-13.1%) and carbohydrates (6.0-11.2%) comprised the largest proportions of total ion intensity (TII). Mass signals with significantly different abundance at the various sampling dates were assigned to compound classes of carbohydrates, phenols and lignin monomers, lignin dimers, lipids, N-containing compounds, sterols, peptides and free fatty acids; these were supplemented by marker signals for N-acetylmuramic acid from bacterial cell walls and signal molecules for the regulation of secondary pathways such as 4-hydroxycinnamic acid and linolenic acid. CONCLUSION Py-FIMS was well suited to detect the molecular-chemical diversity of potato plant rhizodeposits and, compared with traditional a priori analytical methods, provided detailed evidence for significant differences in the composition of rhizodeposits depending on growth stage and diurnal period.

INFLUENCE OF SPECIFIC ORGANIC COMPOUNDS ON PHOSPHORUS SORPTION AND DISTRIBUTION IN A TROPICAL SOIL

Effects of organic matter on phosphorus (P) sorption are not completely understood, among others, because the molecular composition of organic matter seldom has been considered. Our objective was to investigate how surface modification of a tropical soil with specific organic compounds altered the P sorption and distribution of the sorbed P. Samples of an ando-humic Nitisol, original and treated with H2O2 to remove native organic matter, were amended by 50 g C kg−1 from lipids, lignin building blocks, glucose, albumin, tryptophan, histidine, and a mixture of these compounds. Phosphorus sorption was studied by equilibrating 1 g of the treated soil samples in 30 mL of 1 mM CaCl2 · 2H2O containing 0 to 645.71 &mgr;mol P L−1. The P concentrations in the soil solution after 24 h followed the order: histidine > mixture > lignin > albumin > lipid > tryptophan > glucose > control in the original sample and albumin > lignin > lipid > mixture > histidine > tryptophan > glucose > control in the H2O2-treated sample. Phosphorus sorption was lower in the H2O2-treated than in the original sample, which was explained by removal of aluminum and an increase in negative surface charges after native soil organic matter oxidation. The sorbed P distribution, studied by sequentially fractionating the samples with the highest P load, showed that 73 to 96% (original) and ≈100% (H2O2 treated) of sorbed inorganic P was extracted by the first three fractions (anion exchange membrane-Pi, NaHCO3-Pi, NaOH-Pi). From calculations of P requirements for sufficient P concentrations for plant growth, it was concluded that surface modification by the addition of locally available organic compounds with great molecular complexity and organic P constituents may help to reduce the need for mineral P fertilizer and increase its efficiency in tropical soils.

Effects of extracts from Linum usitatissimum on cell vitality, proliferation and cytotoxicity in human breast cancer cell lines

1 Department of Obstetrics and Gynaecology, Faculty of Medicine, University of Rostock, Suedring 81, 18059 Rostock, Germany. 2 Department of Biochemistry, Faculty of Natural Sciences, Institute of Biological Sciences, University of Rostock, AlbertEinstein-Strasse 3, 18059 Rostock, Germany. 3 Institute for Land-Use, Faculty of Agricultural and Environmental Sciences, University of Rostock, Justus-von-LiebigWeg 6, 18059 Rostock, Germany. 4 Department of Cell Biology, Medical Faculty, BMFZ, University of Rostock, Schillingallee 69, 18057 Rostock, Germany.

Pyrolysis-field ionization mass spectrometry and nitrogen K-edge XANES spectroscopy applied to bulk soil leachates—a case study

Although dissolved organic matter (DOM) is an important component of C- and N-fluxes in the environment, its structural composition is still poorly understood due to methodological challenges. We explored the potential of combining pyrolysis-field ionization mass spectrometry (Py-FIMS) and N X-ray absorption near edge structure (N-XANES) spectroscopy to study the molecular-chemical composition of lyophilized bulk soil solution samples that were not subjected to pretreatment like dialysis. Soil leachates were collected at 90 cm and 220 cm depth from an arable and a fallow site. Py-FIMS spectra reflected differences in DOM composition related to land use and sampling depth. Land use effects were expressed in higher abundances of carbohydrates and peptides at the arable than at the fallow site. The relative proportions of carbohydrates decreased and the proportions of lignin-derived compounds increased with depth, indicating a relative enrichment to more stabilized DOM along the flow path. Nitrogen XANES spectra were dominated by the signal of NO(3)-salts but also indicated the presence of organic, non-amidic N as found in imidazoles, pyrazoles, purines and/or nitrile-N, whereas N-compounds like pyridines, pyrroles, quinoline and indole were detected by Py-FIMS. Thus, the combined application of Py-FIMS and N-XANES yielded complementary information regarding the molecular-chemical composition of DOM. Future applications of these techniques may benefit from selectively analyzing soil solution samples with lower nitrate concentrations collected in early spring.

Fast and sensitive in vivo studies under controlled environmental conditions to substitute long-term field trials with genetically modified plants

We introduce an easy, fast and effective method to analyze the influence of genetically modified (GM) plants on soil and model organisms in the laboratory to substitute laborious and time consuming field trials. For the studies described here we focused on two GM plants of the so-called 3rd generation: GM plants producing pharmaceuticals (PMP) and plant made industrials (PMI). Cyanophycin synthetase (cphA) was chosen as model for PMI and Choleratoxin B (CTB) as model for PMP. The model genes are expressed in transgenic roots of composite Vicia hirsuta plants grown in petri dishes for semi-sterile growth or small containers filled with non-sterile soil. No significant influence of the model gene expression on root induction, growth, biomass, interaction with symbionts such as rhizobia (number, size and functionality of nodules, selection of nodulating strains) or arbuscular mycorrhizal fungi could be detected. In vitro, but not in situ under field conditions, structural diversity of the bulk soil microbial community between transgenic and non-transgenic cultivars was determined by PLFA pattern-derived ratios of bacteria: fungi and of gram+: gram- bacteria. Significant differences in PLFA ratios were associated with dissimilarities in the quantity and molecular composition of rhizodeposits as revealed by Py-FIMS analyses. Contrary to field trials, where small effects based on the transgene expression might be hidden by the immense influence of various environmental factors, our in vitro system can detect even minor effects and correlates them to transgene expression with less space, time and labour.