Conservation seed physiology of the ciénega endemic, Eryngium sparganophyllum (Apiaceae)

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.

Evidence of interpopulation variation in the germination of Eryngium maritimum L. (Apiaceae)

“…This supports the hypothesis that E. maritimum seeds are physiological (PD) or morphophysiological dormant (MPD), and so they need a trigger, in this case, a cold stratification period to begin germination. Considering that MPD was reported by Necajeva and Ievinsh (2013), it can be suggested that embryos are incompletely developed as morphophysiological dormant seeds at the end of the fruiting period (Wolkis et al 2020), and so they have to develop during autumn and winter, while they need some high temperatures at spring to begin the germination process (Vandelook et al 2012). Moreover, seeds from the Atlantic population germinated better at 15°C, which could be linked with the same hypothesis, and so suggests that the species has been able to adapt its ecological germination requirements to the specific…”

“…Many species in the Apiaceae are reported to exhibit morphological dormancy (MD) or morphophysiological dormancy (MPD) (Finch-Savage and Leubner-Metzger 2006;Baskin and Baskin 2014), including the Genus Eryngium (Wolkis et al 2020). In MPD, the seed coat is water permeable, embryos are undeveloped and also have a physiological inhibiting mechanism that requires an ecological signal to elicit germination (i.e.…”

Improved two-step analysis of germination data from complex experimental designs

“…To elucidate the effects of gibberellic acid (GA 3 ) on germination, a one-way factorial layout with solutions of 0 (control), 250, 500, 750 and 1000 ppm GA 3 was used. The full experimental design involved two factors but we followed the original analysis described by Wolkis et al (2020). For each solution, there were three replicates of 16 seeds that were sown in 90-mm Petri dishes on silica sand moistened with sterilized distilled water and placed inside a resalable zip-top plastic bag to preserve moisture.…”

“…Example 1: a one-way factorial design Wolkis et al (2020) investigated conservation seed physiology of the ciénega (freshwater emergent wetlands) endemic, Eryngium sparganophyllum (Apiaceae), including storage behaviour and dormancy. In this example, we re-examine the authors' experiment testing germination response to varying concentrations of gibberellic acid.…”

“…This shortcoming has also been noted in other applications of the two-As a consequence, a number of authors have had to resort to simpler solutions to provide visualizations of results obtained from using the two-step meta-analytic approach. Solutions include showing graphs based on simpler model fits that ignore some of the hierarchical structure in the experiment (Rossini et al, 2019;Wolkis et al, 2020) or redrawing fitted curves (without confidence bands) based on the parameter estimates from the two-step approach (Asadi-Sabzi et al, 2020).…”