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We used a combination of field studies and laboratory experiments to characterize key ecological aspects of the seed biology and soil seed bank dynamics of annual plant communities in chenopod shrublands of South Australia. A sequential study of the soil seed bank demonstrated seasonal and between-year variability in numbers and composition of the soil seed bank. Soil samples incubated under different temperature and watering regimes produced different communities, indicating that species respond differentially to various environmental combinations. Emergence was extremely low at low water availability and at high temperatures, even in trays with ample water. A high percentage of seeds of four out of five species buried in the field remained viable for two years, while the fifth, Carrichtera annua, showed a sharp decline in seed viability, reaching nearly zero survivorship. Our results indicate that, in this system, annual plant communities result from germination of a fraction of seeds present in the soil seed bank, when autumn or winter rainfalls occur. Because different species have different responses to various combinations of environmental conditions, the community composition varies from year to year. This variability is likely to be a component of coexistence through the storage effect.
Facelli et al. (Tue,) studied this question.