Microbial utilization and mineralization of [14C]glucose added in six orders of concentration to soil

The substrate availability for microbial biomass (MB) in soil is crucial for microbial biomass activity. Due to the fast microbial decomposition and the permanent production of easily available substrates in the rooted top soil mainly by plants during photosynthesis, easily available substrates make a very important contribution to many soil processes including soil organic matter turnover, microbial growth and maintenance, aggregate stabilization, CO₂ efflux, etc. Naturally occurring concentrations of easily available substances are low, ranging from 0.1 μM in soils free of roots and plant residues to 80 mM in root cells. We investigated the effect of adding ¹⁴C-labelled glucose at concentrations spanning the 6 orders of magnitude naturally occurring concentrations on glucose uptake and mineralization by microbial biomass. A positive correlation between the amount of added glucose and its portion mineralized to CO₂ was observed: After 22 days, from 26% to 44% of the added 0.0009 to 257 μg glucose C g^?1 soil was mineralized. The dependence of glucose mineralization on its amount can be described with two functions. Up to 2.6 μg glucose C g^?1 soil (corresponds to 0.78% of initial microbial biomass C), glucose mineralization increased with the slope of 1.8% more mineralized glucose C per 1 μg C added, accompanied by an increasing incorporation of glucose C into MB. An increased spatial contact between micro-organisms and glucose molecules with increasing concentration may be responsible for this fast increase in mineralization rates (at glucose additions <2.6 μg C g^?1). At glucose additions higher than 2.6 μg C g^?1 soil, however, the increase of the glucose mineralization per 1 μg added glucose was much smaller as at additions below 2.6 μg C g^?1 soil and was accompanied by decreasing portions of glucose ¹⁴C incorporated into microbial biomass. This supports the hypothesis of decreasing efficiency of glucose utilization by MB in response to increased substrate availability in the range 2.6–257 μg C g^?1 (=0.78–78% of microbial biomass C). At low glucose amounts, it was mainly stored in a chloroform-labile microbial pool, but not readily mineralized to CO₂. The addition of 257 μg glucose C g^?1 soil (0.78 μg C glucose μg^?1 C micro-organisms) caused a lag phase in mineralization of 19 h, indicating that glucose mineralization was not limited by the substrate availability but by the amount of MB which is typical for 2nd order kinetics.     

Root Exudation of Organic Acids of Herbaceous Pioneer Plants and Their Growth in Sterile and Non-Sterile Nutrient-Poor, Sandy Soils from Post-Mining Sites

Nutrient-poor, sandy soils form the prevailing substrate at post-mining sites of the Lusatian region(Brandenburg, Germany) and present a challenge for vegetation development. We studied the organic acid quantity and composition of three commonly occurring pioneer plant species, the legumes Lotus corniculatus L. and Trifolium arvense L. and the grass Calamagrostis epigeios(L.) Roth, to determine if plant growth and exudation differed with(non-sterilized soil) and without(sterilized soil) an indigenous soil microbial community. We investigated whether organic acids were found in the rhizosphere and surrounding soil and whether this influenced nutrient mobilization. This study consists of linked field investigations and a greenhouse experiment. Plants were grown in the greenhouse in either sterilized or non-sterilized sandy soil from a reclamation site in the Lusatian mining landscape(Welzow Su¨d, East Germany). After seven months, the plant biomass, root morphology, organic acids, and water-soluble nutrients and root colonization with arbuscular mycorrhizal fungi(AMF) and dark septate endophytes(DSE) were analyzed. Roots of all three plants in the field and greenhouse experiments were highly colonized with AMF. Calamagrostis epigeios and T. arvense had a significantly higher colonization frequency with DSE than L. corniculatus. The quantity and composition of organic acids strongly differed among plant species, with the highest number of organic acids found for L. corniculatus and lowest for C. epigeios. The quantity of organic acids was greatly reduced in all plants under sterilized soil conditions. However, the composition of organic acids and plant growth in sterilized soil were reduced for both legumes, but not for C. epigeios, which had a higher biomass under sterilized conditions. Changes in nutrient concentrations in the field rhizosphere soil relative to those in the control were measurable after seven months. While the spectrum of organic acids and the growth of legumes seemed to be dependent on a highly diverse soil microbial community and a symbiotic partner, the grass C. epigeios appeared capable of mobilizing enough nutrients without an indigenous microbial community, and might be more competitive on sites where soil microbial diversity and activity are low.     

Interactive effects of substrates and ectomycorrhizal colonization on growth of a poplar clone

A balsam poplar clone (Populus trichocarpa cv. Weser 6) was inoculated by two ectomycorrhizal strains (Laccaria bicolor MW 158 and Paxillus involutus 1444) in Kick‐Brauckmann‐pots. The substrates were two arable sandy soils (Cambisols) with different organic matter content and nutrient supply. One soil (WIL) was rich in organic matter (C_org = 1.6%) and total nitrogen (N_t = 0.14%), whereas the other soil (RIE) had low contents of C_org (0.8%) and N_t (0.08%). Leaf nutrient concentrations, shoot lengths, root and shoot biomass production and nitrogen accumulation in the biomass were determined to discover possible inoculation effects. Mycorrhization indices (% colonized fine roots) of 36% with Laccaria bicolor and 40% with Paxillus involutus were observed on the C_org rich soil (WIL) in contrast to 16% and 14% on the C_org poor soil (RIE), respectively. Inoculation of poplar on the soil WIL increased shoot length, biomass production, shoot:root ratio and total N uptake of the cuttings, whereas on the soil RIE only the shoot:root ratio increased and the N nutrition was improved. We conclude that interactions between soil and fungus should be tested when choosing ectomycorrhizal strains for inoculation.     

Hydrogen consumption and carbon monoxide production in soils with different properties

 Soils are the dominant sink in the global budget of atmospheric H₂, and can be an important local source of atmospheric CO. In order to understand which soil characteristics affect the rates of H₂ consumption and CO production, we measured these activities in 16 different soils at 30% and 60% of their maximum water holding capacity (whc). The soils were obtained from forests, meadows and agricultural fields in Germany and exhibited different characteristics with respect to texture, pH, total C, substrate-induced respiration (SIR), respiration, total and inorganic N, N mineralization, nitrification, N₂O production and NO turnover. The H₂ consumption rate constants were generally lower at 60% than at 30% whc, whereas the CO production rates were not influenced by the whc. Spearman correlation analysis showed that H₂ consumption correlated significantly (r>0.5, P<0.05) at both water contents only with SIR and potential nitrification. The correlation with these variables that are largely dominated by soil microorganisms is consistent with our understanding that atmospheric H₂ is oxidized by soil hydrogenases. Multiple regression analysis and factor analysis gave similar results. Production of CO, on the other hand, was significantly correlated to soil total C, respiration, total N and NH₄ ⁺. The correlation with these variables that are largely dominated by a soil's chemical composition is consistent with our understanding that CO is produced by chemical oxidation of soil organic C. CO production was also influenced by soil usage, with rates increasing in the order: arable<meadow<forest. H₂ consumption was not influenced by soil usage. Received: 28 October 1999     

Effect of selenate supplementation on glycoalkaloid content of potato (Solanum tuberosum L.)

Potatoes (Solanum tuberosum L.) supplemented with increasing amounts of sodium selenate were analyzed for glycoalkaloid (GA) content. GAs were extracted with 5% acetic acid from freeze-dried tubers of two potato cultivars, Satu and Sini, harvested 10 weeks after planting as immature. The GAs alpha-solanine and alpha-chaconine were quantified by reverse-phase high-performance liquid chromatography (RP-HPLC) with diode array detection. Two independent experiments were performed. In the first experiment, the total GA concentration +/- standard error of the tubers ranged between 105 +/- 9 and 124 +/- 10 mg kg(-1) fresh weight in Satu and between 194 +/- 26 and 228 +/- 10 mg kg(-1) fresh weight in Sini. The ratio of alpha-solanine to alpha-chaconine was 0.2 in Satu and 0.5-0.6 in Sini. In the second experiment, the total GA concentration +/- standard error was 75 +/- 4 to 96 +/- 11 mg kg(-1) fresh weight, and the ratio of alpha-solanine to alpha-chaconine was 0.3-0.4 in Satu. A high sodium selenate supplementation (0.9 mg of Se kg(-1) quartz sand) slightly decreased the GA content in Satu, but this decrease was not statistically significant. Furthermore, at this addition level the Se concentration increased to a very high level of 20 microg g(-1) dry weight, which cannot be recommended for human consumption. In both experiments, the Se concentration in tubers increased with increasing sodium selenate application levels. Our results show that acceptable application levels of selenate did not have an effect on the GA concentration in immature potato tubers.     

Evolutionary impact assessment: accounting for evolutionary consequences of fishing in an ecosystem approach to fisheries management

Managing fisheries resources to maintain healthy ecosystems is one of the main goals of the ecosystem approach to fisheries (EAF). While a number of international treaties call for the implementation of EAF, there are still gaps in the underlying methodology. One aspect that has received substantial scientific attention recently is fisheries‐induced evolution (FIE). Increasing evidence indicates that intensive fishing has the potential to exert strong directional selection on life‐history traits, behaviour, physiology, and morphology of exploited fish. Of particular concern is that reversing evolutionary responses to fishing can be much more difficult than reversing demographic or phenotypically plastic responses. Furthermore, like climate change, multiple agents cause FIE, with effects accumulating over time. Consequently, FIE may alter the utility derived from fish stocks, which in turn can modify the monetary value living aquatic resources provide to society. Quantifying and predicting the evolutionary effects of fishing is therefore important for both ecological and economic reasons. An important reason this is not happening is the lack of an appropriate assessment framework. We therefore describe the evolutionary impact assessment (EvoIA) as a structured approach for assessing the evolutionary consequences of fishing and evaluating the predicted evolutionary outcomes of alternative management options. EvoIA can contribute to EAF by clarifying how evolution may alter stock properties and ecological relations, support the precautionary approach to fisheries management by addressing a previously overlooked source of uncertainty and risk, and thus contribute to sustainable fisheries.     

Diagnosis and treatment of Neospora caninum infection in a dog

Neospora caninum, a protozoan organism, caused extensor rigidity of the pelvic limbs in a 12-week-old dog. Diagnosis was based on results of muscle biopsy, neuroelectrodiagnostics, serotesting, and cell culture. Indirect fluorescent antibody (IFA) titer to N caninum was 1:800 at time of admission and 1:3,200 after 4 and 6 weeks. A reciprocal IFA titer of 50 to N caninum was also found in the CSF. Serotesting for T gondii was negative. Treatment with clindamycin followed by sulfadiazine and trimethoprim did not change the pelvic limb extensor rigidity, but other signs of minor neurologic dysfunction improved.     

Peripheral hypomyelinization in two golden retriever littermates

Peripheral hypomyelinization was found in 2 Golden Retriever littermates that had pelvic limb ataxia, depressed postural reactions, and depressed segmental reflexes. Diagnostic findings included infrequent denervation potentials, reduced or absent evoked potentials, and markedly diminished motor nerve conduction velocities. Light and electron microscopy of peripheral nerves revealed fewer than normal myelinated axons, myelinated sheaths inappropriately thin for the caliber of the fiber, poor myelin compaction, greater than normal numbers of Schwann cell nuclei, many Schwann cells with voluminous cytoplasm, and greater than normal amount of perineural collagen. Findings were compatible with a peripheral hypomyelinization process; a defect in Schwann cell function was suspected.     

Vertebral lymphosarcoma in a cat

Lymphosarcoma of the cauda equina in a domestic shorthair cat invaded the body of L7 and cranial portion of the sacrum. Clinical signs consisted of acute ambulatory paraparesis, tail paralysis, and dyschezia. Radiographically, there was evidence of bone lysis. Surgical exploration yielded a diagnosis, but did not induce improvement in the cat, which was subsequently euthanatized. Neurologic signs were similar to those associated with sacral nerve root avulsion injuries in cats.     

Genotyping of the fish rhabdovirus, viral haemorrhagic septicaemia virus, by restriction fragment length polymorphisms

The aim of this study was to develop a standardized molecular assay that used limited resources and equipment for routine genotyping of isolates of the fish rhabdovirus, viral haemorrhagic septicaemia virus (VHSV). Computer generated restriction maps, based on 62 unique full-length (1524 nt) sequences of the VHSV glycoprotein (G) gene, were used to predict restriction fragment length polymorphism (RFLP) patterns that were subsequently grouped and compared with a phylogenetic analysis of the G-gene sequences of the same set of isolates. Digestion of PCR amplicons from the full-length G-gene by a set of three restriction enzymes was predicted to accurately enable the assignment of the VHSV isolates into the four major genotypes discovered to date. Further sub-typing of the isolates into the recently described sub-lineages of genotype I was possible by applying three additional enzymes. Experimental evaluation of the method consisted of three steps: (i) RT-PCR amplification of the G-gene of VHSV isolates using purified viral RNA as template, (ii) digestion of the PCR products with a panel of restriction endonucleases and (iii) interpretation of the resulting RFLP profiles. The RFLP analysis was shown to approximate the level of genetic discrimination obtained by other, more labour-intensive, molecular techniques such as the ribonuclease protection assay or sequence analysis. In addition, 37 previously uncharacterised isolates from diverse sources were assigned to specific genotypes. While the assay was able to distinguish between marine and continental isolates of VHSV, the differences did not correlate with the pathogenicity of the isolates.