Investigating the mechanisms for the opposing pH relationships of fungal and bacterial growth in soil     

Johannes Rousk  Philip C. Brookes 《Soil biology & biochemistry》2010,42(6):926-934

Soil pH is one of the most influential variables in soil, and is a powerful factor in influencing the size, activity and community structure of the soil microbial community. It was previously shown in a century old artificial pH gradient in an arable soil (pH 4.0-8.3) that bacterial growth is positively related to pH, while fungal growth increases with decreasing pH. In an attempt to elucidate some of the mechanisms for this, plant material that especially promotes fungal growth (straw) or bacterial growth (alfalfa) was added to soil samples of the pH gradient in 5-day laboratory incubation experiments. Also, bacterial growth was specifically inhibited by applying a selective bacterial growth inhibitor (bronopol) along the entire pH gradient to investigate if competitive interaction caused the shift in the decomposer community along the gradient. Straw benefited fungal growth relatively more than bacterial, and vice versa for alfalfa. The general pattern of a shift in fungal:bacterial growth with pH was, however, unaffected by substrate additions, indicating that lack of a suitable substrate was not the cause of the pH effect on the microbial community. In response to the bacterial growth inhibition by bronopol, there was stimulation of fungal growth up to pH 7, but not beyond, both for alfalfa and straw addition. However, the accumulation of ergosterol (an indicator of fungal biomass) during the incubation period after adding alfalfa increased at all pHs, indicating that fungal growth had been high at some time during the 5-day incubation following joint addition of alfalfa and bronopol. This was corroborated in a time-series experiment. In conclusion, the low fungal growth at high pH in an arable soil was caused to a large extent by bacterial competition, and not substrate limitation.  相似文献   

Loss of low molecular weight dissolved organic carbon (DOC) and nitrogen (DON) in H₂O and 0.5 M K₂SO₄ soil extracts     

Johannes Rousk  Davey L. Jones 《Soil biology & biochemistry》2010,42(12):2331-2335

Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (¹⁴C-glucose, 1 and 100 μM) and DON (¹⁴C-amino acid mixture, 1 and 100 μM) during extraction of soil (0-6 h) with either distilled water or 0.5 M K₂SO₄. The extractions were performed at 20 °C, at 4 °C, or in the presence of an inhibitor of microbial activity (HgCl₂ and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H₂O extracts at 1 μM for both substances (>90% loss after 15 min). Lower temperature (4 °C) and presence of K₂SO₄ both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H₂O or K₂SO₄ extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON.  相似文献   

Korrelationen zwischen den Werten der Saugkraft,der Zellsaftkonzentration und des Feuchtegehaltes in Zuckerrübenblättern und die Abhängigkeit der Zellsaftkonzentration von der Luft- und Bodenfeuchtigkeit     

Johannes Birke 《Archives of Agronomy and Soil Science》2013,59(12):1041-1049

  相似文献   

Autorreferate demnächst erscheinender Arbeiten     

Johannes Birke 《Archives of Agronomy and Soil Science》2013,59(9):679-682

  相似文献   

Polyuria and Polydipsia and Disturbed Vasopressin Release in 2 Dogs With Secondary Polycythemia     

Ilse K. van  Vonderen  Hein P. Meyer  Johannes S. Kraus  Hans S. Kooistra 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1997,11(5):300-303

In dogs, secondary polycythemia (SP) may be associated with polyuria and polydipsia (PU/PD). The pathogenesis of this PU/PD has not yet been explained. We hypothesized that hyperviscosity and increased blood volume in SP might affect vasopressin (VP) release, resulting in PU/PD. This hypothesis was tested in 2 dogs with SP caused by renal neo-plasia and PU/PD. Osmoregulation of VP release was studied by a modified water deprivation test and by investigating the VP response to hypertonic saline infusion.
Water deprivation test results were consistent with an inability to produce concentrated urine despite increasing plasma osmolality. During hypertonic saline infusion, the osmotic threshold of VP release was markedly increased in both dogs, resulting in a delayed VP response to increasing plasma osmolality. The sensitivity of VP release was low normal in both dogs. We conclude that blood hyperviscosity and increased blood volume led to impaired VP release and polyuria.  相似文献   

Is green infrastructure an effective climate adaptation strategy for conserving biodiversity? A case study with the great crested newt     

Astrid J. A. Van Teeffelen  Claire C. Vos  Rene Jochem  Johannes M. Baveco  Henk Meeuwsen  Jelle P. Hilbers 《Landscape Ecology》2015,30(5):937-954

  相似文献   

Biodiversity in cultural landscapes: influence of land use intensity on bird assemblages     

Johannes Rüdisser  Janette Walde  Erich Tasser  Johannes Frühauf  Norbert Teufelbauer  Ulrike Tappeiner 《Landscape Ecology》2015,30(10):1851-1863

  相似文献   

Use of the SDS-sedimentation test and SDS-polyacrylamidegel electrophoresis for screening breeder's samples of wheat for bread-making quality     

Johannes H. E. Moonen  Auke Scheepstra  Aris Graveland 《Euphytica》1982,31(3):677-690

Summary Gelprotein or SDS-insoluble gel-forming glutenin was isolated from wheat flour by extraction with an aqueous 1.5% SDS solution. Remarkable intervarietal differences were observed both in amount and subunit composition of these proteins.The amount of gelprotein and the SDS-sedimentation volume both proved to be good parameters for the bread-making quality of wheat cultivars. A high correlation was observed between amount of gelprotein and SDS-sedimentation volume. The amount of gelprotein was therefore tentatively assumed to be the essential basis of the SDS-sedimentation test.The subunit composition of the gelprotein was studied by SDS-PAGE after reduction of SS bonds by mercaptoethanol. It was found that the average bread-making quality of wheat cultivars and progeny of the cross Atlas 66 x Atys which possessed subunits 3 and 10, coded for by chromosome 1D, was significantly higher than that of wheat samples possessing subunit 2 and 11, their allelic counterparts.  相似文献   

Plant species richness and composition in managed grasslands: The relative importance of field management and environmental factors     

Sebastian Klimek  Anne Richter gen. Kemmermann  Johannes Isselstein 《Biological conservation》2007,134(4):559-570

Decline of grassland diversity throughout Europe within the last decades is threatening biological diversity and is a major conservation problem. There is an urgent need to determine the underlying factors that control vascular plant species richness and composition in managed grasslands. In this study, 117 grasslands were sampled using standardised methods. Explanatory variables were recorded for each grassland site, reflecting the local field management, site-specific environmental conditions and large-scale spatial trends. Using variation partitioning methods, we determined the pure and shared effects of these three sets of explanatory variables on the plant species richness and composition in grasslands. Most of the explained variation in plant species richness was related to the joint effect of local field management and environmental variables. However, the applied variation partitioning approach revealed that the pure effect of spatial variables contributed relatively little to explaining variation in both the plant species richness and species composition. The largest fractions of explained variation in plant species composition were accounted for by the pure effects of environmental and local field management variables. Moreover, the results revealed that the main mechanisms by which these sets of explanatory variables affect plant species vary according to the type of management regime under study. From our findings we could conclude that particularly a reduction of nitrogen fertilisation on meadows and grazing at a low stocking rate on pastures can help to conserve biodiversity.  相似文献   

Genotoxicity of melanoidin fractions derived from a standard glucose/glycine model   总被引：2，自引：0，他引：2  

Taylor JL  Demyttenaere JC  Abbaspour Tehrani K  Olave CA  Regniers L  Verschaeve L  Maes A  Elgorashi EE  van Staden J  de Kimpe N 《Journal of agricultural and food chemistry》2004,52(2):318-323

Genotoxic compounds can act at various levels in the cell (causing gene, chromosome, or genome mutations), necessitating the use of a range of genotoxicity assays designed to detect these different types of mutations. The production of melanoidins during the processing and cooking of foods is associated with changes in their nutritional character, and the discovery of mutagenic substances in pyrolyzed protein and amino acids has raised concern about the safety of these foods. The aim of this work was to test melanoidin fractions in three different in vitro assays (Ames test, Vitotox test, and micronucleus test). These melanoidin fractions were produced from the condensation of glucose with glycine and their separation was conducted by dialysis. The crude reaction mixture (before dialysis) and both the LMW and HMW fractions obtained by dialysis showed no genotoxicity in these assays, despite being tested at concentrations much higher than those naturally found in food products. The LMW fraction, however, showed toxicity at these high concentrations. The volatile fraction produced in this reaction showed genotoxicity only in the Vitotox test, at high concentrations.  相似文献