1,720,966 research outputs found
Influence of soil acidity on depth gradients of microbial biomass in beech forest soils
No full textThe objectives of the study were to investigate mineral soil profiles as a living space for microbial decomposers and the relation of microbial properties to soil acidity. We estimated microbial biomass C on concentration (mu g g(-1) DW) as well as on volume basis ( g m(-2)) and the microbial biomass C to soil organic C ratio along a vertical gradient from L horizon to 20 cm in the mineral soil and along a gradient of increasing acidity at five beech forest stands in Germany. Microbial biomass C concentration ranged from 17,000 - 34,000 mu g C-mic g(-1) DW in the litter layer and decreased dramatically down the profile to 29 - 264 mu g C-mic g(-1) DW at 15 - 20 cm depth in the mineral soil. This represents depth gradients of microbial biomass C concentrations ranging from a factor of 65 in slightly acidic and up to 875 in acidic soils. In contrast, microbial biomass C calculated on a volume basis ( g C-mic m(-2)) showed a different pattern since a considerable part of the microbial biomass C was located in the mineral soils. In the soil profile 22-34% of the microbial biomass C was found in the mineral soil at strictly acidic sites and as much as 64 - 88% in slightly acidic soils. The microbial biomass C to soil organic carbon ratios decreased in general down from the L horizon in the forest floor to 0 - 5 cm depth in the mineral soils. In strongly acidic mineral soils however, the C to soil organic carbon ratio increased with depth, suggesting a positive relation to increasing pH. We conclude from depth gradients of soil pH and microbial biomass C to soil organic carbon ratio that pH affects this ratio at acidic sites. The inter-site comparison indicates that acidity restricts microbial biomass C in the mineral soils
Manganese toxicity in epiphytic lichens: chlorophyll degradation and interaction with iron and phosphorus
No full textConcentrations of chlorophylls a and b decreased with increasing MnCl2 supply in the zepiphytic lichen Hypogymnia physodes, but not in Lecanora conizaeoides. The reduction of chlorophyll concentrations in. H. physodes was as strong (chlorophyll a) or even; stronger (chlorophyll b) as in samples treated with CuCl2. FeCl3 compensated for MnCl2-induced chlorophyll degradation in H. physodes. Furthermore, MnCl2-induced growth inhibition of soredia cultivated on agar plates was alleviated by FeCl3. These results suggest that Mn causes intra cellular Fe deficiency in H. physodes. A soredia growth test with MnCl2 and KCl in combination proved that mitigating effects of FeCl3 were not just caused by reduced chemical activity of Mn2+ due to the addition of another salt. Furthermore, the test showed that Cl- did not inhibit soredia growth. High FeCl3 concentrations applied alone or in combination with MnCl2 were even more detrimental to H. physodes than MnCl2. MnCl2 did not affect the concentrations of ATP, ADP and AMP in H. physodes. This suggests that Mn uptake does not induce intracellular P deficiency in H. physodes despite that Mn is known to be immobilized with P in H. physodes in intracellular polyphosphate granules and in extracellular encrustations. (C) 2002 Elsevier Science B.V. All rights reserved
Relation between respiration, ATP content, and Adenylate Energy Charge (AEC) after incubation at different temperatures and after drying and rewetting
No full textTemperature, drying, and rewetting are important climatic factors that control microbial properties. In the present study we looked at the respiration rates, adenosine 5'-triphosphate (ATP) content, and adenylate energy charge, (AEC) as a measure for energy status of microbial biomass in the upper 5 cm of mineral soils of three beech forests at different temperatures and after rewetting. The soils differed widely in pH (4.0 to 6.0), microbial biomass C (92 to 916 mug (g DW)(-1)) and ATP content (2.17 to 7.29 nmol ATP (g DW)(-1)). The soils were incubated for. three weeks at 7 degreesC, 14 degreesC, and 21 degreesC. After three weeks the microbial properties were determined, retaining temperature conditions. The temperature treatment acid not significantly affect AEC or ATP content, but respiration rates increased significantly with increasing temperature. In a second experiment the soils were dried for 12 hours at 40 degreesC. Afterwards the soils were rewetted and microbial properties were monitored for 72 hours. After the drying, respiration rates dropped below the detection limit; but within one hour after rewetting respiration rates increased above control level drying reduced AEC by 16 % to 44 % and ATP content by 47 % to 7.8 %, respectively. Rewetting increased AEC and ATP content significantly as compared to dry soil, but after 72 hours the level of the controls was still not reached. The level of AEC values indicated dormant cells, but ATP content increased. These results indicate that he microbial carbon turnover was not directly linked to microbial growth or microbial energy, status. Furthermore our results indicate that AEC may describe an average energy status but does not reflect phases of growing, dormant, or dying cells in the complex microbial populations of soils
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Adenylates as an estimate of microbial biomass C in different soil groups.
No full textAdenylate (i.e. adenosine tri- (ATP), di- (ADP) and monophosphates (AMP)) and microbial biomass C data were collected over a wide range of sites including forest floor layers and forest, grassland and arable soils. Microbial biomass C was measured by fumigation extraction and adenylates after alkaline Na3PO4/DMSO/EDTA extraction and HPLC detection. Our aims were (1) to test whether the sum of adenylates is a better estimate for microbial biomass than the determination of ATP, (2) to compare our conversion values with those proposed by others, and (3) to analyse whether soil properties or land use form affect the relationships between ATP, adenylates and microbial biomass C. A close relationship was found between microbial biomass C and ATP (r = 0.96), but also with the sum of adenylates (r = 0.96) within all appropriately conditioned soil samples (n = 112). In the mineral soil (n = 98), the geometric means of the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were 7.4 and 11.4 mumol g(-1), respectively. The mean ratios did not differ significantly between the different texture classes and land use forms. In the forest floor, the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were both roughly two-thirds of those of the mineral soil. The average adenylate energy charge (AEC) of all soil samples was 0.79 and showed a strong negative relationship with the soil pH (r = -0.69). However, the AEC is presumably only indirectly affected by the soil pH. (C) 2003 Elsevier Ltd. All rights reserved
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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