Germination ecology and seedling survival of the critically endangered Glyptostrobus pensilis

Glyptostrobus pensilis is a critically endangered relict conifer characterized by extremely poor natural regeneration, widely recognized as the primary cause for its endangered status. This study investigates seed biological traits, population variation, environmental requirements, and stress responses during germination and early seedling establishment. The aim is to elucidate the mechanisms underlying regeneration failure and to provide scientific guidance for conservation strategies and artificial regeneration. Seeds from the three populations showed high abortion rates, with the Pingnan population (Fujian) exhibiting the highest overall seed quality. Cone morphology was strongly associated with seed abortion, and TTC staining revealed multiple embryo viability states. Two germination types were observed: (1) radical emergence developed normally, and (2) plumule emergence failed to establish, indicating a critical bottleneck during the transition to seedling growth. Some ungerminated seeds remained viable, suggesting possible dormancy or delayed germination. Intact seeds performed significantly better than de-winged and de-coated seeds. Temperature had contrasting effects: 30 °C accelerated germination, while 20 °C promoted both germination and successful seedling establishment. Light did not affect germination onset, but continuous darkness prevented seedling establishment. Shallow sowing (1 cm) enhanced germination and emergence, whereas deeper sowing inhibited emergence. Seeds were highly sensitive to water stress: drought and salinity completely suppressed germination, and prolonged flooding reduced germination and shoot growth, although short-term flooding had limited impact. H₂O₂ disinfection significantly improved germination and seedling establishment. Under simulated post-dispersal habitat conditions, high temperatures favored seed germination, whereas low temperatures strongly suppressed germination but resulted in a higher proportion of viable embryos. Drought inhibited germination even under favorable temperatures, but GA₃ partially alleviated this inhibition and accelerated germination, whereas 2,4-D suppressed germination. Overall, natural regeneration in G. pensilis is constrained by the limited availability of viable seeds due to extensive seed abortion, contrasting germination patterns resulting in different seedling establishment success, and generally low seedling establishment.