Effects of Ovule Position on Seed Maturation, Seed Mass, and Seedling Size in Eastern Redbud (Cercis canadensis)

Abstract

Premise of research. Seed ontogeny between fertilization and seed maturity is a neglected life history stage in demographic studies, yet this period may have profound consequences for seed set and seedling vigor. For plant species with multiovulate linear fruits, it is possible to record the relative position of each ovule, thereby allowing investigators to assess whether ovule development occurs at random or whether it exhibits unique discernible patterns within fruits. We studied effects of ovule position on patterns of ovule development, seed mass, and seedling size within linear pods of Cercis canadensis.Methodology. Fruits were collected from multiple trees at each of three sites in southeastern Michigan. Intraovary ovule position and developmental fate (i.e., undeveloped ovule, aborted ovule, insect-damaged seed, and mature seed) and seed mass were determined. Seedling performance from three seed size classes was also monitored. Seedling traits included days to emergence, height, leaf area, and seedling biomass.Pivotal results. Three-fourths or more of all ovules within fruits across the populations reached seed maturity. Patterns of seed maturation and abortion were nonrandom and significantly depended on populations, individuals, and ovule positions within fruits. Probability of seed maturation within individual fruits was lowest at the basal end and highest at either the center or the distal end, suggesting the existence of a fertilization gradient. Conversely, frequencies of undeveloped ovules and aborted seeds were highest at the bases of fruits. Insect-damaged seeds accounted for 1%–3% of all ovules and occurred randomly. Seeds located in basal sections of fruits were also smaller than seeds located in central and distal sections. Seed mass was positively correlated with all measures of seedling performance.Conclusions. Patterns of ovule development and seed maturation were determined to be nonrandom within fruits of C. canadensis. Ovule position influences abortion and maturation of seeds, seed mass, and early seedling vigor and has the potential to affect overall plant fitness.