Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Soil seed bank

Understanding the persistence of seeds within the soil seed bank is a fundamental requirement for understanding plant population dynamics. Knowledge about seed longevity can help determine whether species can potentially re-establish from seeds stored in the seed bank after local extinction events. Seed longevity was studied for the following six species of dry calcareous grassland: Carlina vulgaris, Daucus carota, Hypochoeris radicata, Pimpinella saxifraga, Succisa pratensis and Tragopogon pratensis. Workpackages 2-6 collected seeds from the UK, The Netherlands, Germany, Sweden and the Czech Republic. These seeds were air-dried, and sent, under standardised packing conditions, to the UK, where they were stored at room temperature until used for experiments. Prior to use in experiments, initial percentage viability levels were determined for seeds of all species collected from all countries.

Seeds were subjected to one of four treatments: (i) burial in the field for 7 months, (ii) burial in the field for 19 months, (iii) storage under ideal conditions to preserve viability in the Millennium Seed Bank (MSB), Wakehurst Place, for 7 months, (iv) storage under ideal conditions at MSB for 19 months. Seeds placed under field conditions were sewn into nylon bags with a small volume of soil, and buried at a depth of 5 cm in dry calcareous grassland field sites. The turf was replaced after burial of the seeds. Seeds to be stored at MSB were first dried through a series of reduced relative humidity rooms, and then vacuum-sealed in light-proof bags. They were then stored within the MSB vault at -20 degrees Celsius.

After retrieval from the burial treatments, seeds were rinsed free of soil and test-crushed for viability. Seeds stored at MSB were brought back to room temperature, and tested for germination in a controlled environment room. At the end of the period allowed for germination, seeds that had not germinated were checked for viability using the crush test.

In the burial treatments all species exhibited reductions in viability over time. Viability of Daucus carota decreased during the first 7 months, but remained stable thereafter. Differences in seed viability due to country of origin were seen in all species, but the differences were not consistent across species. For most species from most countries of origin, storage under ideal conditions at the MSB resulted in little if any reduction in viability over time.

Exceptions that did exhibit declining viability included Succisa pratensis seeds from the UK and the Netherlands, and Tragopogon pratensis ssp. pratensis. Results from the seed burial treatments indicated that a considerable number of seeds of all species examined would be capable of remaining viable under field conditions for at least 19 months. Daucus carota can be characterised as having a long-term seed bank. It was confirmed that the conditions of storage at the MSB are successful in maintaining viability of the majority of the species we tested. Variation in maintenance of viability of seeds of the same species collected from different countries demonstrates that checks of the viability of stored seeds may need to be done on a population or country basis rather than at the level of species, to avoid failure to detect loss through time of stored seeds.

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University of Sussex
School of Life Sciences
BN1 9QG Brighton
United Kingdom