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Freezing sensitivity

Conservation in a seedbank requires seeds to be tolerant of both drying and freezing.

Some rainforest seeds don’t tolerate the drying necessary for seed banking. We’ve found others will tolerate the drying process but then don’t survive freezing! We now need to look inside these rainforest seeds1 to see what is happening as they freeze and thaw.

To do this, we’re using a differential scanning calorimeter (DSC)2. This machine can be used to lower the temperature of a seed sample to -150°C and then raise it back to room temperature. The machine records any sudden changes in energy of the seed as it freezes and thaws and the exact temperatures at which those energy changes happen. This information will help us to determine the critical temperatures at which seed damage occurs for a given species and will allow us to customise storage conditions for that species.

One familiar native plant that falls in this ‘freezing sensitive’ category is the macadamia. All four species of macadamia – Macadamia integrifolia, M. jansenii, M. ternifolia and M. tetraphylla – are native to Australian rainforest and all are threatened in the wild. We’re now using cultivated nuts supplied by the Macadamia Conservation Trust, private growers, and the Department of Primary Industries at Alstonville, to see exactly what happens to the seed as it freezes and thaws. We’ll then use that information to develop storage methods that can be used to conserve the wild species.

Determining whether rainforest seeds can be stored in the seedbank usually requires a series of time-consuming and sometimes inconclusive germination tests. To reduce the time and labour involved, and fast-track our conservation efforts, we’re also trialling use of the DSC to rapidly screen species for freezing sensitivity. Some of the seeds for this part of the project are being provided through a 5-yr collaboration to conserve tropical mountain rainforest plants led by the Australian Tropical Herbarium  and funded by The Ian Potter foundation.

Learn more about the DSC and seedbanking in our Branch Out podcast
1‘Looking inside rainforest seeds’ is a 3-yr project funded by The Ian Potter Foundation.

2The differential scanning calorimeter was kindly donated by the Foundation and Friends of the Botanic Gardens.