Impact of nitrogen deposition on the species richness of grasslands

A transect of 68 acid grasslands across Great Britain, covering the lower range of ambient annual nitrogen deposition in the industrialized world (5 to 35 kg Nha–1 year–1), indicates that long-term, chronic nitrogen deposition has significantly reduced plant species richness. Species richness declines as a linear function of the rate of inorganic nitrogen deposition, with a reduction of one species per 4-m2 quadrat for every 2.5 kg Nha–1 year–1 of chronic nitrogen deposition. Species adapted to infertile conditions are systematically reduced at high nitrogen deposition. At the mean chronic nitrogen deposition rate of central Europe (17 kg Nha–1 year–1), there is a 23% species reduction compared with grasslands receiving the lowest levels of nitrogen deposition

Ellenberg N value, tissue chemistry and soil chemistry 15 years after the cessation of nitrogen addition

Background & Aims The consequences of fertiliser addition to semi-natural grasslands are well understood, but much less is known about the consequences of cessation of nitrogen fertiliser regimes, including rates of recovery. This study aimed to investigate whether the effects of nitrogen (N) additions to a mesotrophic grassland were still apparent 15 years after the cessation of N inputs. Methods A long-term experiment at Tadham Moor, UK, received N additions at rates of 0, 25, 50, 100 and 200 kg N ha−1 yr−1 between 1986 and 1994. Fifteen years after the cessation of N additions soil chemistry, plant tissue chemistry, plant biomass and Ellenberg N values were assessed. Results KCl-extractable ammonium-N, total soil N, total organic carbon and microbial biomass N differed between the controls and the higher historic levels of N addition. Plant tissue chemistry showed no significant effects of previous N addition. Above-ground biomass was higher where N had been added, although this response was only weakly significant. The species composition of the vegetation showed effects of the N addition with mean Ellenberg N values significantly higher than the control in most treatments. Conclusion The effects of long-term N addition can be seen for many years

Cathodoluminescence microanalysis of electron irradiation damage in wide band gap materials

Cathodoluminescence (CL) microanalysis (spectroscopy and microscopy) in an electron microscope enables both pre-existing and irradiation induced local variations in the bulk and surface defect structure of wide band gap materials to be characterized with high spatial (lateral and depth) resolution and sensitivity. CL microanalytical techniques allow the in situ monitoring of electron irradiation induced damage, the post irradiation assessment of damage induced by other energetic radiation, and the investigation of irradiation induced electromigration of mobile charged defect species. Electron irradiated silicon dioxide polymorphs and MeV H+ ion implanted Type Ila diamond have been investigated using CL microanalytical techniques

Maximum likelihood estimation in multidimensional scaling

lognormal, hypothesis testing, implicit equation,