Germination physiology of Cochlospermum fraseri (Bixaceae), a deciduous tree from Northern Australia with physical seed dormancy

Michael Just; Shane Turner; Adam Cross; Wolfgang Lewandrowski; Simone Pedrini; Kingsley Dixon

doi:10.1093/conphys/coad057

Germination physiology of Cochlospermum fraseri (Bixaceae), a deciduous tree from Northern Australia with physical seed dormancy

Conserv Physiol. 2023 Sep 1;11(1):coad057. doi: 10.1093/conphys/coad057. eCollection 2023.

Authors

Michael Just¹, Shane Turner¹, Adam Cross^{1

2}, Wolfgang Lewandrowski^{3

4}, Simone Pedrini¹, Kingsley Dixon¹

Affiliations

¹ School of Molecular and Life Sciences, Curtin University, Kent Street, Bentley, Western Australia 6102, Australia.
² Ecological Health Network, 1330 Beacon St, Suite 355a, Brookline, Massachusetts 02446, United States of America.
³ Department of Biodiversity, Conservation and Attractions, Kings Park Science, Fraser Avenue, Kings Park, Western Australia 6005, Australia.
⁴ School of Biological Sciences, University of Western Australia, Stirling Highway, Crawley, Western Australia 6009, Australia.

Abstract

Cochlospermum fraseri ('Kapok', Bixaceae) is a deciduous tree widely distributed throughout semi-arid and monsoon tropical northern Australia, and an important species for ecological restoration in the region. We aimed to better understand the seed biology and ecology of C. fraseri to determine the mechanisms by which seed dormancy might be alleviated, and the conditions that support germination to inform the use of this species in restoration. Dormancy breaking treatments (wet heat, dry heat, scarification) commonly applied to species with physical seed dormancy (PY) were tested along with stratification at 5-35°C (nine treatments). Following dormancy alleviation, seeds were germinated at nine temperatures (5 to 40°C) and five water potentials (0 to -0.8 MPa) to understand environmental thresholds that regulate germination physiology in non-dormant seeds. A proportion of seeds (<0.3) lose dormancy naturally in response to warm (25 to 35°C) moist conditions, which dislodges the hypostase plug that prevents water uptake, whilst neither dry (≥100°C) nor wet (~100°C) heat were effective. Dormancy loss was also achieved by exposing seeds to concentrated (95-98% v/v) sulphuric acid for 3-7 hours, after which high proportions (>0.75) of germination were observed. Cochlospermum fraseri seeds possess PY, which is alleviated by seasonal temperatures that occur when soil moisture is high, allowing seeds to employ a risk-adverse strategy and maximize establishment success in episodic environments with stochastic rainfall events. The understanding of dormancy alleviation requirements gained here adds to our knowledge of PY worldwide and recruitment dynamics in the Australian monsoonal tropics and will aid land managers and restoration practitioners by informing both seeding sites and optimal time for in situ sowing as well as the potential capacity of this species to form a persistent soil seed bank.

Keywords: Dormancy; Northern Australia; physiology; restoration; thermal performance.