EGRO-project Summer 1995 : report of a six month project in Great Britain

This is a report of a six month project in the summer of 1995 at the Institute of Grassland and Environmental Research (IGER)/ North Wyke Station, Devon, Great Britain. The project is part of the fullfillment of a degree in biology at the University of Groningen (RUG, The Netherlands). To examine the effects of high nutrient input on seed viability, nylon mesh bags with seeds of selected semi-natural grassland species were buried on plots treated with N, P, K fertilizer at five sites in The Netherlands and Great Britain. Before burial a blank germination test in the laboratory took place. The fertilizing started in spring 1993 and will be repeated each year of the project. The seeds will be exhumed at each of four periods (year 1, 2, 4 and 8) and tested on their viability by means of germination. This year the first seed samples were exhumed and tested. The results show that there are no significant differences in viability of the seeds between the different treatments within the species of a site and between the treatments within the sites. However, there are significant differences in germination percentages between the blank germination test and the exhumed seeds. There are also significant differences between the species within the treatments and within the sites. Statistical analysis also shows significant differences in germination of the seeds of the same species and origin between the sites.

Release from native root herbivores and biotic resistance by soil pathogens in a new habitat both affect the alien Ammophila arenaria in South Africa

Many native communities contain exotic plants that pose a major threat to indigenous vegetation and ecosystem functioning. Therefore the enemy release hypothesis (ERH) and biotic resistance hypothesis (BRH) were examined in relation to the invasiveness of the introduced dune grass Ammophila arenaria in South Africa. To compare plant–soil feedback from the native habitat in Europe and the new habitat in South Africa, plants were grown in their own soil from both Europe and South Africa, as well as in sterilised and non-sterilised soils from a number of indigenous South African foredune plant species. While the soil feedback of most plant species supports the ERH, the feedback from Sporobolus virginicus soil demonstrates that this plant species may contribute to biotic resistance against the introduced A. arenaria, through negative feedback from the soil community. Not only the local plant species diversity, but also the type of plant species present seemed to be important in determining the potential for biotic resistance. As a result, biotic resistance against invasive plant species may depend not only on plant competition, but also on the presence of plant species that are hosts of potential soil pathogens that may negatively affect the invaders. In conclusion, exotic plant species such as A. arenaria in South Africa that do not become highly invasive, may experience the ERH and BRH simultaneously, with the balance between enemy escape versus biotic resistance determining the invasiveness of a species in a new habitat. [KEYWORDS: Coastal foredunes; Invasive plants; Plant-parasitic nematodes; Plant–soil feedback; Species diversity