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Some like it cold - unlocking the secrets of alpine seeds

by Trust scientists Dr Amelia Martyn, Dr Karen Sommerville & Dr Cathy Offord

Temperature is a critical factor influencing plant regeneration and nowhere is this more evident than in Australia’s Snowy Mountains, where the depth and duration of snow cover influences which plants are able to grow where. As a result, alpine ecosystems are very sensitive to environmental change and are particularly threatened by warming temperatures.

In February 2004 and 2007, Trust seed collectors Richard Johnstone and Andrew Orme visited the Snowy Mountains and collected seed from a variety of herbs growing at high altitude in Kosciuszko National Park. The seeds were dried, packaged and then stored in the NSW Seedbank at the Australian Botanic Garden as part of an ongoing project to preserve the native species of NSW. An important part of this seedbanking process is ensuring the species collected are able to grow; however, it was found to be very difficult to get some of the alpine seeds to germinate at all.

In a project funded by the Australian Flora Foundation and the Australian Native Plant Society, Canberra, germination specialist Amelia Martyn began a series of experiments to unlock the secrets of the alpine seeds. There followed years of testing, waiting and watching while seeds were given long periods of chilling followed by warm temperatures designed to mimic the seasons in the Snowy Mountains. With the help of dedicated seed bank technicians Veronica Viler, Leah Seed and Allison Frith, Amelia diligently recorded the emergence of the tiny roots and shoots that signalled the beginning of germination. She also recorded the size and weight of seeds from each plant, and the size and shape of the embryos within, in an attempt to find a relationship between the seeds’ germination needs and their physical characteristics.

Each species had a unique response to temperature, with some germinating during the chilling cycle at 5°C, some requiring chilling followed by warm spring temperatures, and some indifferent to the temperatures tested. Two species were unable to germinate at all without chilling, while others germinated much faster and in far great numbers if they were chilled before exposure to warmer temperatures. The requirement for chilling makes these species particularly vulnerable to a warming climate.

Conservation scientist Karen Sommerville joined the team to examine the data for connections between seed characteristics and germination requirements. Seeds with tiny embryos surrounded by endosperm (nutritive tissue) were found to be most likely to require chilling. Seeds without endosperm tended to germinate at a wide range of temperatures whether previously chilled or not. Species in the latter group (including members of the Asteraceae and Rosaceae families) are likely to remain stable or expand in range under a warming climate. Species in the former group (including members of the Apiaceae and Campanulaceae families) are more likely to contract in range in response to warming temperatures, especially if they are already restricted to high-altitude sites. These species should be prioritised for seedbanking as an ‘insurance policy’ against their extinction in the wild.

eyebright
Euphrasia (eyebright) is very difficult to germinate and requires further investigation. Photo: K. Downs.

Andrew-Orme
Seed collector Andrew Orme in the Snowy Mountains. Photo: Euan Mills.

mountain-celery
Aciphylla glacialis (mountain celery) requires very low temperatures for germination. Image: K. Downs.