Effects of nitrogen deposition on soil and vegetation in primary succession stages in inland drift sands

Background and aims Primary succession was studied in acid inland drift sands. Main research questions were: 1) How do vegetation and soil change during succession? 2) How are soil parameters and species abundance affected by atmospheric nitrogen deposition? Methods One hundred sixty-five plots were selected in 21 drift sands throughout The Netherlands, divided over eight succession stages from bare sand to dry heath and within a gradient in nitrogen deposition. Vegetation development and soil parameters were described and water-extractable elements measured and differences between high (>30 kg N ha−1 year−1) and lower nitrogen deposition sites calculated. Results Vegetation cover and height increased during succession. Lichens contributed most to plant species diversity. Thickness of Ah horizon increased and pH decreased and concentrations of Fe, Al, S increased. Base cations increased as well, despite the drop in pH. Also, water-extractable ammonium, nitrate and phosphate increased, along with the NH4:NO3 ratio. Sites with high nitrogen deposition had higher NH4:NO3 and Al:Ca ratios, lower pH, higher cover of algae, lower lichen and total species diversity, more Pinus sylvestris seedlings and more species of late succession stages. Conclusions Drift sand succession seems to be mainly driven by an increase in organic matter, but is accelerated by nitrogen deposition

A Novel Extracytoplasmic Function (ECF) Sigma Factor Regulates Virulence in Pseudomonas aeruginosa

Next to the two-component and quorum sensing systems, cell-surface signaling (CSS) has been recently identified as an important regulatory system in Pseudomonas aeruginosa. CSS systems sense signals from outside the cell and transmit them into the cytoplasm. They generally consist of a TonB-dependent outer membrane receptor, a sigma factor regulator (or anti-sigma factor) in the cytoplasmic membrane, and an extracytoplasmic function (ECF) sigma factor. Upon perception of the extracellular signal by the receptor the ECF sigma factor is activated and promotes the transcription of a specific set of gene(s). Although most P. aeruginosa CSS systems are involved in the regulation of iron uptake, we have identified a novel system involved in the regulation of virulence. This CSS system, which has been designated PUMA3, has a number of unusual characteristics. The most obvious difference is the receptor component which is considerably smaller than that of other CSS outer membrane receptors and lacks a β-barrel domain. Homology modeling of PA0674 shows that this receptor is predicted to be a bilobal protein, with an N-terminal domain that resembles the N-terminal periplasmic signaling domain of CSS receptors, and a C-terminal domain that resembles the periplasmic C-terminal domains of the TolA/TonB proteins. Furthermore, the sigma factor regulator both inhibits the function of the ECF sigma factor and is required for its activity. By microarray analysis we show that PUMA3 regulates the expression of a number of genes encoding potential virulence factors, including a two-partner secretion (TPS) system. Using zebrafish (Danio rerio) embryos as a host we have demonstrated that the P. aeruginosa PUMA3-induced strain is more virulent than the wild-type. PUMA3 represents the first CSS system dedicated to the transcriptional activation of virulence functions in a human pathogen

Biodiversiteitsgraadmeters Fryslân : status en trend van hoofd-natuurtypen en soorten

De graadmeter bestaat uit twee delen, een deel bevat informatie over de voor- of achteruitgang van soorten (zoals vogels, vlinders en zoogdieren), het tweede deel bevat informatie over de natuurkwaliteit en het oppervlak natuur. Informatie van soorten en de natuurkwaliteit is gebaseerd op veldwaarnemingen. Zowel de natuurkwaliteit als het oppervlak natuur worden vergeleken met een ongestoorde situatie. Voor het agrarisch gebied is een aparte referentie gebruikt. De gebruikte methode maakt het mogelijk om de Friese situatie qua biodiversiteit te spiegelen aan het verleden en aan de landelijke situatie. Het aandeel van het Friese grondgebied met min of meer natuurlijke ecosystemen, exclusief (half)natuurlijk grasland, bedraagt nu circa 48%. De toename in de oppervlakte natuur is sinds de introductie van de EHS in Fryslân groter dan landelij