Abstract
Knowledge of seed dormancy and optimal propagation techniques is crucial for successful ex situ restoration and reintroduction projects, and determining the seed storage behaviour of a species is critical for the long-term conservation of seeds, further supporting future ex situ efforts. Eryngium sparganophyllum (Apiaceae) is a globally critically endangered plant species endemic to ciénega wetlands of southwest North America. To support in situ and ex situ conservation efforts of E. sparganophyllum, we asked (i) how does the embryo: seed (E:S) ratio change over time once imbibed, (ii) how does germination respond with varying periods of exposure to cold (5°C) and warm (25°C) stratification, and concentrations of gibberellic acid (GA3). By answering these questions, (iii) can dormancy class be inferred, and (iv) what storage behaviour category is exhibited? To answer these questions, we collected seeds in Southern Arizona from one of the few remaining wild populations. We measured embryo growth and tested the effects of cold (0–18 weeks) and warm (0 and 4 weeks) stratification, and 0–1000 ppm gibberellic acid on germination. We also tested the effects of cold (−80°C) dry (~20% equilibrium relative humidity) storage on germination. We found that (i) embryos grow inside seeds prior to germination; (ii) compared to control, cold stratification for at least 6 weeks increased germination and warm stratification had no effect; (iii) 1000-ppm GA3 had the highest germination success; (iv) therefore this species exhibits morphophysiological dormancy; and (v) seeds are orthodox and can therefore be conserved using conventional storage methods. This information will aid managers in the propagation of E. sparganophyllum that is crucial for in situ reintroduction and restoration projects, and seed banking represents a critical ex situ conservation strategy for the preservation of this species.
Highlights
Species specific knowledge of seed storage behaviour and dormancy release are essential for successful ex situ species conservation and in situ reintroduction and restoration projects
E. sparganophyllum populations have been extirpated from two of its six historic locations due to the loss of ciénega habitat owing to groundwater depletion and alterations of waterways (Stromberg et al, in press)
Time to 50% germination (t50) was not biologically meaningful since t0 differed for each length of time in cold stratification and has been omitted
Summary
Common practices involved in managing species of conservation importance include seed collecting, banking and propagation (Guerrant et al, 2004; Convention on Biological Diversity, 2011; Center for Plant Conservation, 2019). Species specific knowledge of seed storage behaviour and dormancy release are essential for successful ex situ species conservation and in situ reintroduction and restoration projects. As well as seed storage behaviour in wild species has been studied in detail, many species specific knowledge gaps exist (Walters et al, 2005; Baskin and Baskin, 2014). One such species is Eryngium sparganophyllum Hemsl. E. sparganophyllum is a globally critically endangered (NatureServe Web Service, 2019) plant with narrow habitat specificity in ciénegas (freshwater emergent wetlands) restricted to the southwestern USA and northern Mexico. E. sparganophyllum populations have been extirpated from two of its six historic locations due to the loss of ciénega habitat owing to groundwater depletion and alterations of waterways (Stromberg et al, in press)
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