Gibberellic acid and light effects on seed germination in the seagrass <i>Zostera marina</i>

Seagrass meadows have been heavily affected by human activities, with Zostera marina L. (Zosteraceae) being one of the most impacted species. Seed-based methods are currently the preferred approach for their restoration, yet low germination rates and poor seedling establishment remain significant challenges. This study explored the combined effects of light spectra (white, red, and darkness), photoperiod, and gibberellic acid (GA_3-0, 50, 500, and 1000 mg L^-1) on Z. marina seed germination using a fully crossed incubation experiment. Penalised logistic regression and Cox proportional hazards analysis were chosen to account for low germination events and to analyse the temporal dynamics of germination. We found that light conditions, particularly red light and darkness, when combined with GA₃, significantly enhanced germination probability. Furthermore, mid (50 mg L^-1) and high (500 mg L^-1) GA₃ concentrations reduced time-to-germination. Morphometric analysis of the cotyledonary and leaf tissue development indicates no adverse effects of the treatments on seedling development. Our findings suggest that light and GA₃ treatments effectively improve germination success and reduce dormancy in Z. marina seeds. Seed treatments can mitigate stress- or manipulation-induced dormancy and can represent a viable strategy for on-demand germination, such as in the context of seed-based restoration efforts.