Relationship between flooding regimes, time of year, and seed coat characteristics and coloration within fruits of the annual monocarpic plant sesbania emerus (Fabaceae)

Premise of research. Many plant species produce propagules of different shapes and sizes on the same plant or within an inflorescence. These differences influence seed dispersal and germination and seedling growth. We investigated the relationship between the flooding regime, time of the fruiting season, and position within the fruit on seed coloration, seed abortion, and seed predation in Sesbania emerus. Methodology. We studied the production of seeds of different colors within fruits of S. emerus in Palo Verde National Park, Costa Rica, during the months of fruit maturation and seed dispersal. We sampled fruits in natural stands along a flooding gradient, and for each seed, we recorded the color of its coat, its position within the pod, and whether it was healthy, aborted, or predated. We also studied the structure of seed coats of seeds of different colors using scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) to determine their chemical characteristics. Pivotal results. Our study reveals that S. emerus produced seeds of different colors within the same fruit and that their proportion varied along a flooding gradient and during the fruiting season. The proportion of seeds of different colors also varied among the positions within the fruit. Seed abortion and seed predation predominantly occurred for brown seeds and changed between flooding levels and fruiting season. SEM showed no differences in the seed coats’ thicknesses or structures among seed colors, but TGA showed differences in water, cellulose, hemicellulose, and lignin content. Conclusions. The production of seeds of different colors in S. emerus is related to differences in the flooding regime, time within the fruiting season, and position within the fruit. Seed color affects seed germination and the likelihood of seed abortion and predation, and we discuss the potential factors determining these differences.