A Comparative Study of Germination Biology and Plant Performance in Two Dry Grassland Species

Over the last 20 years, the species assemblage of the species-rich dry grassland communities of central Germany has changed due to the ongoing abandonment of traditional land-use practices. In our study we wanted to investigate the germination biology and the plant-plant interaction of the low-growing and declining forb Alyssum montanum and the increasingly dominant grass Festuca rupicola. To investigate the germination behaviour we simulated cold (8/4°C), warm (20/10°C) and hot (32/20°C) conditions under a light-dark regime (12/12 hours) as well as in constant darkness. Germination of both species was similar with almost all non-dormant seeds germinating under intermediate temperature conditions (20/10°C). Whereas F. rupicola (F) germinated equally well under light changing conditions and constant darkness, the germination of A. montanum (A) was clearly reduced in darkness, which implies a strong competitive advantage of F. rupicola in dense vegetation cover. However, A. montanum germinated early under all temperatures regimes and better under 20/10°C as well as with light changing conditions. The interactions between the two species were tested in a pod-experiment with a replacement design, within which the composition of individuals was changed in the following way: 4A/1F, 3A/2F, 2A/3F, 1A/4F (eight replications per each). To evaluate any influence of intraspecific competition we created monocultures in an additive design (1A, 2A, 3A, 4A, 5A, 1F, 5F; eight replications per each). Despite that A. montanum developed faster and flowered after only four months in the replacement design experiment, the herb responded negatively to the presence of F. rupicola in several parameters (number of flowers, number of fruits and biomass per individual). The calculation of the Relative Neighbour Effect (RNE) indicated facilitation for F. rupicola and competition on A. montanum, which increased with increasing number of individuals of the other species. Our data suggest that A. montanum seedling recruitment, growth and fitness are negatively affected by increasing vegetation density of the expanding grass species F. rupicola.