Overstory-specific effects of litter fall on the microbial carbon turnover in a mature deciduous forest

Mature deciduous forests can serve as important carbon (C) sinks, but the C storage differs significantly in dependency on the tree species. To specify the significance of overstory-specific effects of litter fall on the soil microbial C turnover, we have investigated the ¹³C isotopic signature of microbial biomarker phospholipid fatty acids (PLFAs). Samples were taken under pure Fagus sylvatica and mixed overstory (F. sylvatica and Fraxinus excelsior or F. excelsior, Acer spp. and F. sylvatica) in a mature temperate deciduous forest in Central Germany 4 weeks prior to and 3 weeks after litter fall. Accordingly, the CO₂ emission from soil was measured before, during and after the litter fall to investigate the response of decomposition. At all sites and at both sampling dates the fungal biomarker PLFA 18:2ω6,9 had predominantly lower δ¹³C values (from −32 to −43‰) than the bacterial biomarker PLFAs (δ¹³C values from −23 to −39‰). This difference indicated that fungi generally used preferentially plant derived C, whereas the bacterial populations include groups which used SOM derived C, independent on the overstory trees. Under pure F. sylvatica overstory the δ¹³C values of microbial biomarker PLFAs were slightly decreased (up to 2‰ for 17:0br) or unchanged after litter fall. By contrast, under both variants of mixed overstory the δ¹³C values of biomarker PLFAs of fungi (18:2ω6,9) were increased after litter fall (+3.5 and +3.8‰). This might be explained partly by a faster initial decomposition of foliar litter from mixed overstory already during litter fall as confirmed by higher CO₂ emission under mixed F. excelsior, Acer spp. and F. sylvatica than under pure F. sylvatica in this period. However, the involved microbial populations differed overstory-specific. Bacterial biomarker PLFAs with strongest overstory-specific differences in the response on litter fall were 17:0br (Gram-positive bacteria), 18:1 and 19:0cy (Gram-negative bacteria). The present results indicate that a tree species conversion even exclusively between deciduous tree species might alter the soil microbial C turnover during litter decomposition and suggest that it would in the long-term change the SOM stability and C storage.     

Distribution of total mercury in coastal sediments from Jade Bay and its catchment, Lower Saxony, Germany

Purpose

Sediment cores provide a reliable record of mercury (Hg) contamination and can be used to study long-term Hg pollution and relevant environmental change. In the last hundred years, there were several events which may have contributed to the accumulation of Hg in Jade Bay and its catchment. This work was undertaken to assess the record in total Hg (THg) content in sediments of cores from Jade Bay and its catchment.

Materials and methods

A 5-m sediment core from Jade Bay, Lower Saxonian Wadden Sea, southern North Sea and a 12-m core from its catchment area (Wangerland, coastal zone of the Jade Bay) were used to study Hg contents in sediments. Total Hg, grain size distribution, aluminium (Al) and total organic carbon (TOC) were analysed on subsamples of both sediment cores. Total Hg was determined by oxygen combustion-gold amalgamation using DMA-80.

Results and discussion

As THg contents of the Jade Bay core were positively correlated to the sum of TOC and Al contents (r ²?=?0.86, p?<?0.001), the Hg data were interpreted using a regional normalisation function with the sum of Al and TOC as the normalisation parameters. Total Hg contents of the Wangerland core were correlated better to Al contents (r ²?=?0.70, p?<?0.001) than to the sum of TOC and Al contents (r ²?=?0.63, p?<?0.05). Therefore, Hg contents in sediments of the Wangerland core were normalised to Al contents. Comparison between enrichment factors and the background range of the sediment cores suggested that Jade Bay was contaminated about 50 years ago, and that Wangerland, or the catchment area of Jade Bay, was contaminated about 300 years ago, if no diagenetic remobilization occurred.

Conclusions

Total Hg contents of both cores were low and of no concern to the aquatic environment of Jade Bay. The Hg record was in good agreement with the history of industrial development in the region; thus, Hg deposition could have occurred through atmospheric input, ammunition residues of the Second World War and volcanic emanations, as well as through diagenetic remobilization.     

Chemical changes during the production of thermo-treated beech wood

Thermal treatments of beech wood with different temperature loads on the wood cause characteristic changes in the chemical composition. The determination of specific changes was carried out by means of suitable methods, both wet chemical and instrumental analyses. It could be confirmed that in addition to the degradation of polyoses, lignin, known as the thermally most stable compound, shows significant thermal alterations too.     

Beobachtungen über den Käferflug vonAnthrenus verbasci L. undAnthrenus pimpinellae F.

Zusammenfassung Bei den beiden Anthrenusartenverbasci undpimpinellae wurden Käferflug, Eiablage und Ursprungsort beobachtet. Folgende Feststellungen konnten gemacht werden:1. Fast ansschließlich wurden kleinblütige, weiße Blütenstände angeflogen.2. Es wurden solche Blütenstande (Dolden oder Rispen) bevorzugt, die über der Laubzone der betreffenden Pflanze stehen.3. BeiSpiraea wurde nur die weiße, nicht aber die rote Spielart aufgesucht.4. Die Weibchen vonA. verbasci legen ihre Eier nach dem Blütenbesuch ab.5. Die Weibchen vonA. pimpinellae legen ihre Eier vor dem Blütenbesuch ab.6. An den Ursprungsorten der Käfer wurden Eilarven nur vonA. pimpinellae festgestellt.     

Studies on milled wood lignins from spruce part 1. Composition and molecular properties

Summary Isolation of six milled wood lignins (MWL) from spruce under different conditions resulted in variable yields between 2.2% and 11.8% related to wood lignin. The composition of crude and purified lignins was evaluated with regard to non-hydrolyzable residue, acid-soluble lignin and polysaccharide content, which varied from 0.9 to 2.5%, depending on isolation conditions. The polysaccharide moiety of the crude and purified lignins contained a high percentage of glucose, probably derived from cellulose. The molecular size distributions determined by gel chromatography on different gels showed a broad distribution for all isolated lignins. A probable maximum of 40,000 for the molecular weight of milled wood lignins was determined by ultracentrifugation. Some of the lignin fractions were examined in the electron microscope.The authors are indepted to Prof. E. Killmann and Mrs. M. Bäumle (Institute for Technical Chemistry, Technical University of Munich) for assistance with the ultracentrifuge measurements and Dr. M. Stoll for precious suggestions and discussions. Submitted by Deutsche Forschungsgemeinschaft (DFG).     

Penetration studies of propoxur and phoxim from eggshell into whole egg after experimental exposure and application in henhouses

The penetration of propoxur and phoxim from eggshell into whole egg was investigated in vitro by spraying eggs directly and in vivo after application of the compounds in henhouses. Although mean concentrations of the compounds on eggshells were up to 23000 microg kg(-1), mean residue concentrations in whole eggs were far below the current maximum residue levels (50 microg kg(-1) for propoxur and 60 microg kg(-1) for phoxim). These results provide the first evidence that propoxur and phoxim do not penetrate from eggshell into whole egg under experimental and field conditions. Subsequently, residue carry-over after egg cracking in households and during a worst-case situation in an egg-cracking plant was investigated. However, when eggs were cracked manually, a negligible contamination of whole egg values occurred. If, in an automated process, eggshells accidentally come into close contact with whole egg, very high residue levels of propoxur and phoxim may be generated time dependently. These results suggest that eggshell contact with whole egg during egg cracking must be avoided to prevent pesticide carry-over.     

Analysis of fatty aldehyde composition, including 12-methyltridecanal, in plasmalogens from longissimus muscle of concentrate- and pasture-fed bulls

In a large study, 64 German Holstein and German Simmental bulls were randomly allocated to either an indoor concentrate system or periods of pasture feeding followed by a finishing period on a concentrate containing linseed to enhance the contents of beneficial fatty acids in beef. This paper reports the diet effects on the concentration of 12-methyltridecanal (12-MT) and further fatty aldehydes released from plasmalogens in the phospholipids of longissimus muscle of the bulls. Because of the trace level of the important odorant 12-MT in beef, the determination of fatty aldehydes in phospholipids was done by acidic hydrolysis and the reaction of the aldehydes with 2,4-DNPH followed by high-pressure liquid chromatography (HPLC) analysis. The diet affected the 12-MT concentrations in the muscle phospholipids of both breeds. Pasture feeding significantly increased the 12-MT concentrations up to 350 microg/100 g fresh muscle in the muscle phospholipids of German Holstein and German Simmental bulls as compared with the concentrate-fed bulls. Furthermore, pasture feeding resulted in a significant increase of n-octadecanal in the muscle phospholipids of both breeds up to 39.5 mg/100 g fresh muscle. The concentration of n-hexadecanal was not affected by the diet. Pasture feeding as compared to concentrate feeding significantly decreased the concentration of n-octadec-9-enal in the muscle phospholipids. Summarizing, pasture feeding increased the 12-MT concentration, which can be associated with meat of more intensive aroma and better taste.