15N stable isotope labelling of slugs (Gastropoda: Pulmonata)

Stable isotope tracers are a promising tool for investigating the ecology of terrestrial slugs, including predator‐prey relationships, migration behaviour, nutrient turnover and dietary routing. The objective of the present feasibility study was to label two economically important slug groups, Deroceras reticulatum and keeled slugs (families Limacidae and Milacidae, respectively), with the stable isotope ¹⁵N under controlled laboratory conditions. Significant isotopic enrichment in slug tissue was detected after 4 days and persisted for at least 10 days after slugs had been fed on ¹⁵N enriched food for a period of 15 days. The time course of ¹⁵N uptake into slug tissues and its relation to food consumption were well described mathematically. Estimated mean ¹⁵N assimilation efficiencies from labelled maize mixed with unlabelled wheat bran were 30% and 38%, respectively, for the species groups studied. These findings suggest that slugs can be readily and efficiently labelled and that it is feasible to devise protocols for producing large numbers of isotopically labelled slugs for use in ecological studies. A simple method is described for the collection and analysis of cutaneous mucus from individual slugs which can be used to test uniformity of isotopic labelling.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Time course of signal transduction in phytochrome-mediated anthocyanin synthesis in mustard cotyledons

Abstract. The effectiveness of phytochrome (Pfr) in mediating anthocyanin synthesis in epidermal cells of mustard ( Sinupis alba L.) cotyledons is strongly increased by a light pretreatment of the seedling prior to competence (Mohr et al. , 1979; Johnson, 1980). Here we test the hypothesis that the observed 'sensitivity amplification' is related to a change in the time course of signal transduction from phytochrome to the responsive cell function. It was found that the time course of escape from photoreversibility—considered to reflect the time course of signal transduction—is not changed by a light pretreatment, although the rate of signal transduction increases with age and depends strongly on the level of Pfr.     

Rediscovery of Paramecium nephridiatum Gelei, 1925 and its Characteristics

Paramecium nephridiatum Gelei. 1925, was rediscovered. It is a euryhaline brackish-water species that morphologically resembles Paramecium woodruffi . but with multiple contractile vacuole pores. The general morphology, morphometry. and random amplified polymorphic DNA (RAPD) fingerprint patterns are presented for a number of the stocks collected around the world.     

Taurine Transport in N-deprived Chlorella fusca

The development of taurine uptake into the unicellular greenalga Chlorella fusca 211-8b was characterized as a specificresponse to either nitrate or sulphate limitation. Taurine transportunder nitrogen starvation was stimulated by low pH and showeda biphasic kinetics with K_m-values of 1.1 x 10^–3 mol dm^–3and 1.0 x 10^–2 mol dm^–3. Uptake was substantiallyinhibited by all - and ß-amino acids tested, whereassulphonate analogues failed to diminish taurine accumulation.Thus, uptake seemed to be mediated by a ‘general aminoacid permease’, unable to discriminate between carboxyland sulphonyl groups. However, Chlorella fusca could not catabolizethis unusual ß-amino acid and mobilize the amino-boundnitrogen for growth. Only a small group of -amino acids supportedthe growth of Chlorella fusca as an efficient nitrogen source. Key words: Taurine uptake, nitrogen starvation, amino acid uptake, Chlorella fusca.     

How far do experimentally elevated CO2 levels reach into the surrounding? – An example using the 13C label of soil organic matter as an archive

During the last two decades, free air CO₂ enrichment (FACE) studies have been conducted to study the effects of rising atmospheric CO₂ concentrations on ecosystems. The distances between fumigated and control plots differ widely among those projects, but no experimental data are available how far into the surrounding area an effect of CO₂ fumigation can be detected. As the CO₂ gas added to the fumigated plots has a different ¹³C label than ambient atmospheric CO₂, its carbon can be traced into plants and soil organic matter (SOM). The Swiss FACE in Eschikon had been conducted for 10 years on a grassland site. After it had ended, we analysed soil samples from three transects extending from the plots to the surrounding area for their organic carbon (C_org) content and carbon isotopic signature. We determined the maximum spatial extension to which carbon originating from the fumigation was incorporated into SOM. A budget of the fumigation gas‐derived C_org in the upper 10 cm of the soil showed that approximately 50 kg C were stored within the plots, and an additional 31 kg C were stored in their immediate surroundings up to a distance of 9 m from the gas pipes. The presented approach provides us with a method to determine a posteriori the extension to which the CO₂ fumigation treatment contaminated its immediate surroundings during a FACE experiment. In the presented example, this showed that the distances between plots could have been reduced significantly. Although not generalizable to other experimental settings, the finding indicates that optimizing the spatial layout, e.g. by modelling gas dispersion, will be useful when planning future large‐scale FACE infrastructures. Our approach provides a solid basis to test such gas‐dispersion models on existing FACE sites before planning new sites.     

Isolation and characterization of microsatellite loci from Macadamia

Thirty‐three microsatellite loci were isolated for the Australian rainforest tree Macadamia integrifolia. Genotyping across a test panel of 43 commercial cultivars generated an average polymorphic information content of 0.480. Five loci showed no polymorphism across cultivars. Significant linkage disequilibrium was detected in 10 pairwise comparisons, including two pairs of loci identified from the same clone sequence. The 33 microsatellite loci represent a significant tool for genome mapping and population genetic studies.