AOBPreview originally published online on June 16, 2008
Annals of Botany 2008 102(2):255-264; doi:10.1093/aob/mcn087
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Interaction Between Seed Dormancy-release Mechanism, Environment and Seed Bank Strategy for a Widely Distributed Perennial Legume, Parkinsonia aculeata (Caesalpinaceae)
1 CSIRO Entomology, Indooroopilly, Queensland, Australia
2 CRC for Australian Weed Management
3 Weed Management Branch, Berrimah, Northern Territory, Australia
* For correspondence. E-mail rieks.vanklinken{at}csiro.au
Received: 14 March 2008 Returned for revision: 24 April 2008 Accepted: 12 May 2008 Published electronically: 16 June 2008
Background and Aims Parkinsonia aculeata: (Caesalpinaceae) is a perennial legume with seeds that have hard-seeded (physical) dormancy and are potentially very long-lived. Seed dormancy is a characteristic that can both help maximize the probability of seedling establishment and spread the risk of recruitment failure across years (bet-hedging). In this study, dormancy-release patterns are described across the diverse environments in which this species occurs in order to test whether wet heat (incubation under wet, warm-to-hot, conditions) alone can explain those patterns, and in order to determine the likely ecological role of physical dormancy across this species distribution.
Methods: A seed burial trial was conducted across the full environmental distribution of P. aculeata in Australia (arid to wet-dry tropics, uplands to wetlands, soil surface to 10 cm deep).
Key Results: Wet heat explained the pattern of dormancy release across all environments. Most seeds stored in the laboratory remained dormant throughout the trial (at least 84 %). Dormancy release was quickest for seeds buried during the wet season at relatively high rainfall, upland sites (only 3 % of seeds remained dormant after 35 d). The longest-lived seeds were in wetlands (9 % remained dormant after almost 4 years) and on the soil surface (57 % after 2 years). There was no consistent correlation between increased aridity and rate of dormancy release.
Conclusions: The results suggest that physical dormancy in P. aculeata is a mechanism for maximizing seedling establishment rather than a bet-hedging strategy. However, seed persistence can occur in environmental refuges where dormancy-release cues are weak and conditions for germination and establishment are poor (e.g. under dense vegetation or in more arid micro-environments) or unsuitable (e.g. when seeds are inundated or on the soil surface). Risks of recruitment failure in suboptimal environments could therefore be reduced by inter-year fluctuations in microclimate or seed movement.
Key words: Bet-hedging, dormancy-release mechanisms, environmental refuges, legume, Parkinsonia aculeata, physical dormancy, seed bank persistence, seed burial depth, seed dormancy, tropical wetlands, wet heat, variable environment
Present address: School of Natural and Rural Systems Management, The University of Queensland, St Lucia, Queensland, Australia
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