In East Germany, a high percentage of species-rich, semi-natural dry grasslands has been converted into species-poor communities dominated either by Poa angustifolia or Festuca rupicola. The disappearance of low-intensity types of agricultural land-use such as mowing and grazing has been the cause for the decline of many grassland species, as lack of biomass extraction leads to a new situation in competition. Here we evaluate the performance of the rare forb Campanula glomerata in competition with P. angustifolia and F. rupicola using a replacement design experiment. C. glomerata responded to the presence of these grass species in contrasting ways: whereas the presence of P. angustifolia had a negative effect on C. glomerata biomass and fitness, the presence of F. rupicola affected the forb in a positive way. The results of an additional sowing experiment revealed that the germination and establishment rates of C. glomerata decrease in accordance with increasing density of P. angustifolia. Thus the response of this rare forb varies among neighbour species.
Salt tolerance of halophytes corresponds with the habitat requirement of the species. It is an important factor during the germination phase and it can determine successful establishment. This paper presents the effects of alternating temperaturelight regimes (4/8°C, 10/20°C, 20/32°C; 12 h dark: 12 h light) and different salinity levels (0, 200, 400, 600 mmol l 21 NaCl) on seed germination of five halophytes, Halimione pedunculata, Bupleurum tenuissimum, Aster tripolium, Triglochin maritimum and Armeria maritima. The five species differ with respect to family and life-form and spatially correspond to a decreasing salt gradient (i.e. distance from salt water, with H. pedunculata being the most tolerant and A. maritima being the least). Armeria maritima, A. tripolium and T. maritimum seeds were additionally subjected to a cold stratification experiment. The results showed that Halimione pedunculata, an annual therophyte of year-round heavily saline habitats, was dormant under all experimental conditions. Bupleurum tenuissimum, a species typical to sites of varying salinity prone to leaching during spring and autumn rainfall, germinated best under cold and warm temperatures, but only under non-saline conditions. Aster tripolium and T. maritimum, close neighbours in salt marshes, showed very similar germination behaviour: seeds of both species tolerated high levels of salinity and germinated best in summer temperatures during periods of highest soil salinity, and germination was significantly promoted by cold. Armeria maritima, a species usually found on the marginal fringes of saline habitats, germinated only under low salt levels and maximum germination was under cold (spring) and warm (autumn) temperatures, with no significant effect of cold stratification.
The disappearance of low-intensity types of agricultural land use such as mowing and grazing is a global phenomenon which leads to changes in species composition and interactions in plant communities. In central Germany, formerly species-rich, semi-natural dry grasslands have been converted into species-poor communities dominated by Festuca rupicola or Poa angustifolia. As a consequence, several forbs have become endangered, and biodiversity has decreased. In a 5-year competition experiment (replacement design; pots were placed outdoors at Halle Botanical Garden), we evaluated the performance of plant-plant interactions between the rare forb Campanula glomerata, F. rupicola and P. angustifolia, respectively. The response of C. glomerata to the presence of the two grass species were measured by stem length, number of flowers and above-ground biomass annually harvested. We did not find significant differences in C. glomerata stem lengths between years and treatments, but flower production, which was highest in the first year, strongly decreased in the subsequent years. Moreover, flower production was lower in combination with P. angustifolia than with F. rupicola. Biomass production showed significant differences between years, but not between treatments. The positive and negative interactions between C. glomerata and the two grass species was estimated by calculating Relative Neighbour Effect Index (RNE). In combination with F. rupicola, interactions switched between facilitation and competition from year to year. In the presence of P. angustifolia, competitive effects on C. glomerata were highest in the second year, but declined from year to year. Curiously, there were no significant correlations between positive and negative interactions with climatic conditions (annual temperature, precipitation and relative air humidity). Our results showed that the response of the rare forb C. glomerata varies with neighbour species, and that fecundity is more prominently affected by competition than stem height or biomass. Our data indicate that biomass removal by traditional land use methods would facilitate the restoration of species-rich dry grassland communities.
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.
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