Starving for oxygen: the effect of hypoxia on seed germination and secondary dormancy induction in Mediterranean temporary ponds plant species

Mediterranean temporary ponds (MTPs) are dynamic habitats where low levels of dissolved oxygen can significantly impact plant life. This study investigated the effect of hypoxia and near-anoxia on seed germination and the induction of secondary dormancy in 14 plant species, characteristic of this habitat. Imbibed seeds were subjected to various oxygen concentrations (0.1, 5, 10, or 21% O2), in both light and darkness. We also tested seed ability to recover germination by moving them to aerobic conditions. We measured embryo growth after hypoxic treatments and during recovery in three species with morpho-physiological dormancy, a rarely investigated response in this dormancy class. Our findings revealed a wide range of species-specific responses. Hypoxia did not inhibit germination in half of the tested species in the light, while near-anoxia completely inhibited germination in all species. However, most seeds fully recovered germination ability once aerobic conditions were restored. Interestingly, hypoxia in darkness reduced or prevented germination in some species and specifically induced secondary dormancy in Juncus bufonius. Surprisingly, seeds of Bulliarda vaillantii lost their light requirement for germination under hypoxia. In three Ranunculus species with morpho-physiological dormancy, hypoxia slowed embryo growth, which delayed germination recovery. This study reveals that MTPs species have evolved adaptations, ranging from tolerance to hypoxic conditions, to the ability to trigger secondary dormancy, which are crucial to surviving and reproducing in these unique environments. The results offer new insights into the germination ecophysiology of MTPs species and their regeneration niche in temporary wetlands.