Abstract
The direct role of physical dormancy in delaying germination of Serianthes grandiflora Bentham, Serianthes kanehirae Fosberg, and Serianthes nelsonii Merrill seeds has not been adequately studied, nor has the role of temperature on germination behaviors. Imbibition testing indicated seeds with scarified testa absorbed water for the duration of a 24 h imbibition period, but seeds with an intact testa stopped absorbing water after 1 h. The behavior of S. nelsonii seeds most closely matched those of S. kanehirae, with the pattern of water absorption for S. grandiflora seeds deviating from that for the other species. Scarified seeds germinated readily, with initial germination occurring by 50 h for S. nelsonii and 90 hr for the other species, and maximum germination of 80% to 90% occurring by 60 h for S. nelsonii and 100 h for the other species. Predicted optimum temperature based on a fitted quadratic model was 26 °C for S. nelsonii, 23 °C for S. grandiflora, and 22 °C for S. kanehirae. Seed respiration increased within 3 h of imbibition for scarified seeds and continued to increase in a linear pattern. The linear slope was greatest for S. nelsonii, intermediate for S. grandiflora, and least for S. kanehirae, but ultimate respiration was greatest for S. kanehirae seeds. Seed respiration was so limited for un-scarified seeds that the instrument was unable to quantify any carbon dioxide efflux. Physical dormancy in seeds of these Serianthes species is a powerful trait that spreads out the timing of seedling emergence in natural settings and controls imbibition and germination speed in managed nurseries.
Highlights
Serianthes nelsonii is a critically endangered legume tree species restricted to the islands of Guam and Rota [1]
A greater understanding of S. nelsonii germination requirements may aid in understanding the limitations to recruitment in natural settings and improve methods in conservation nurseries
The pattern of water absorption for water absorption for S. grandiflora followed a cubic model with an ultimate absorption of about 150%
Summary
Serianthes nelsonii is a critically endangered legume tree species restricted to the islands of Guam and Rota [1]. The populations are not regenerating, and seedlings that emerge in situ exhibit rapid mortality [2,3,4]. Thousands of propagated individuals will be required to fulfill the goals of the published species recovery plan [5,6], illuminating the mandate to successfully germinate thousands of seeds in managed nurseries. The seed-to-seedling transition is of critical importance, is the initial phenological transition of a sexually-propagated plant, and the underlying requirements for this transition are some of the most important seed traits related to plant fitness [7]. A greater understanding of S. nelsonii germination requirements may aid in understanding the limitations to recruitment in natural settings and improve methods in conservation nurseries
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