Coping with stressful environments: An experimental study of seed germination and seedling survival of Mexican riverweeds under natural conditions

Seed germination and seedling survival are fundamental processes in the life cycle of Podostemaceae, the largest family of strictly aquatic angiosperms. However, few studies to date have addressed seed germination and seedling survival of Podostemaceae under natural conditions. To fill this gap, we performed a field experiment to study the seed germination and seedling survival of Marathrum foeniculaceum and Noveloa coulteriana, two species of Podostemaceae, in two rivers with contrasting light incidence, the Boca de Tomatlan (BT) and Las Juntas del Tuito (LJ) Rivers, in Jalisco, Mexico. We found significant differences in the final proportion of seeds germinated between M. foeniculaceum (67.74%) and N. coulteriana (32.5%), and the proportion of seeds germinated in the BT river (higher light incidence) was significantly higher than in the LJ river. Likewise, seeds germinated more quickly in M. foeniculaceum than in N. coulteriana, and in the BT river than in the LJ river. Final seedling survival of both M. foeniculaceum and N. coulteriana was rather low (2.53% and 1.08%, respectively), but no significant differences were detected between species or rivers. This paper represents one of the first studies to experimentally evaluate aspects of the ecophysiology of seed germination and seedling survival of Podostemaceae under natural conditions, and it contributes to our understanding of the ecology and conservation of this particular family of plants.