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The role of local adaptation and factors other than climate in determining extinction probabilities of species under climate change has not been yet explicitly studied. Here we performed a field experiment with annual plants growing along a steep climatic gradient in Israel to isolate climatic effects for local trait expression. The focus trait was seed dormancy, for which many theoretical predictions exist regarding climate-driven optimal germination behaviour. We evaluated how germination is consistent with theory, indicating local adaptation to current and changing climatic conditions, and how it varies among species and between natural and standardised soil conditions. We reciprocally sowed seeds from three or four origins for each of three annual species, Biscutella didyma, Bromus fasciculatus and Hymenocarpos circinnatus, in their home and neighbouring sowing locations along an aridity gradient. Our predictions were: lower germination fraction for seeds from more arid origins, and higher germination at wetter sowing locations for all seed origins. By sowing seeds in both local and standard soil, we separated climatic effects from local conditions. At the arid sowing location, two species supported the prediction of low germination of drier seed origins, but differences between seed origins at the other sites were not substantial. There were no clear rainfall effects on germination. Germination fractions were consistently lower on local soil than on standard soil, indicating the important role of soil type and neighbour conditions for trait expression. Local environmental conditions may override effects of climate and so should be carefully addressed in future studies testing for the potential of species to adapt or plastically respond to climate change. [ABSTRACT FROM AUTHOR]

Empirical evidence suggests that the direction and intensity of plant-plant interactions may depend on the favourability of the environment. Previous studies have mainly focused on steep gradients of environmental stress or disturbance, while the interplay of competition and environment has not been tested for subtle environmental differences. Here, we present results from a study on plant communities of temporary wetlands in East-German farmland. Due to yearly ploughing in autumn, the vegetation is composed of annual species. Flooding does not affect adult plants and the elevation on the gradient expresses differences in the length of the growing season rather than in disturbance intensity or severe environmental stress. We tested whether such subtle differences in environmental stress may affect the importance of interspecific competition by the dominant species. Two treatments were applied at two elevations: removal of the dominant species (Matricaria maritimassp.inodora) and reciprocal transplants of the seed-bank of the two elevations. At both elevations, removal ofMatricaria inodoraled to an increase in total species richness and number of wetland species, but the effects were substantially stronger at high elevations. Removal and the elevation on the flooding gradient significantly influenced the plant community composition. In particular, the weed communities became more similar to the wetland communities after the removal. Transplanted weed species did not emerge at low elevations. While two of four target species had significantly higher densities after the removal at high elevations, none of them was influenced by removal at low elevations. This indicates that, consistent with previous studies from other habitat types, competition by the dominant species was more intense under conditions of low environmental stress. The overall results suggest that both flooding as well as interspecific competition are important in structuring the plant communities along the freshwater gradient studied. [ABSTRACT FROM AUTHOR]