Light, temperature, and substrate effects on the germination of three Bromus species in comparison with their abundance in the field

The landscape in the northern Negev Desert of Israel consists of small patches of dwarf shrubs separated by a matrix of biological soil crusts. Bromus species, important winter annuals, are very common in shrub patches and in places where the soil crust has been disturbed. Therefore, patch properties such as substrate and microclimate may have important effects on the size of the seed bank, germination, and seedling establishment of these species. We studied germination under laboratory conditions in light and darkness, at different temperatures, and on various substrates collected from the Sayeret Shaked Long Term Ecological Research (LTER) station. We compared the experimental results with findings of the distribution of abundance of the species in the field. Germination in all three Bromus species responded to light and temperature. The seeds germinated faster in darkness below 20°C, but more rapidly in the light at 20°C. Different constant temperatures not only influenced the rate of germination, but also the start and the time to achieve 75% and 100% germination. The differences in the occurrence of B. alopecuroides and B. fasciculatus in the Sayeret Shaked LTER station may not depend on the substrate. The highest germination (96-100%), with no significant differences, occurred on all substrates except for sterile organic matter, which resulted in 64-66% germination. Comparing these results with the findings of germination abundance in the field, the differentiating factor may be related to the number of seeds that arrive and remain in the different patch types, which in turn depends either on the numbers of seeds produced per plant or on their dispersability or protection against removal. Nevertheless, B. rubens did show significant differences between the two patch types.