Australian Journal of Botany Australian Journal of Botany Society
Southern hemisphere botanical ecosystems
RESEARCH ARTICLE

Are we underestimating the impact of rising summer temperatures on dormancy loss in hard-seeded species?

Anne Cochrane
+ Author Affiliations
- Author Affiliations

Western Australian Department of Parks and Wildlife, Science and Conservation Division, Locked Bag 104, Bentley Delivery Centre, WA 6983, Australia. Email: anne.cochrane@dpaw.wa.gov.au

Australian Journal of Botany 65(3) 248-256 https://doi.org/10.1071/BT16244
Submitted: 6 December 2016  Accepted: 1 April 2017   Published: 16 May 2017

Abstract

Short duration dry heat shock similar to the heat of fire is known to be effective in alleviating physical dormancy in seeds, but are we underestimating the impact of the cumulative heat dose of summer soil temperatures on dormancy loss in hard-seeded species in the context of a changing climate? This study investigated short and long duration dry heat treatments in seeds of four Acacia species (Fabaceae) from South-West Western Australia. Seeds were treated at 90, 100, 110 and 120°C for 10 and 180 min (‘fire’) and at fluctuating temperatures of 30/20, 55/20, 65/20°C for 14, 28, 56 and 112 days (‘summer’). The non-dormant seed fraction of each species was low, but seeds were highly viable after scarification. The results indicate the presence of species-specific temperature thresholds for dormancy loss with duration of heating slightly less important than temperature for dormancy break. Seeds remained highly viable after all long duration treatments but short duration heat shock treatments above 110°C resulted in increased seed mortality. Although cumulative periods of lower fluctuating temperatures were less effective in breaking physical dormancy than the heat of fire in three of the four species, more than 40% of seeds of Acacia nigricans (Labill.) R.Br. lost dormancy after 28 days at 65/20°C. These potentially disturbing findings suggest that long hot summer conditions may compromise soil seed bank longevity over time and may be detrimental to the bet-hedging ability afforded by a hard seed coat in some species in the face of climate warming forecasts for the region.

Additional keywords: Acacia, germination, global warming, physical dormancy, South-West Western Australia.


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