PROXIMATE LIMITS TO SEED PRODUCTION IN A HERBACEOUS PERENNIAL LEGUME, LATHYRUS-VERNUS

Resources, pollen, and predation limit fruit and seed set in Lathyrus vernus. Removal of flowers increased fruit and seed set among remaining ovaries and ovules, but did not affect seed mass. The distributions of the increased fruit and seed set among remaining ovaries indicated specific and variable patterns of translocation. The importance of pollen relative to resource deficiency varied between two experimental seasons, among individuals, and among flowers within shoots. Pollen supplementation increased fruit and seed set in one of two experimental seasons. When shoots were supplied with extra pollen a greater proportion produced fruits, but the number of fruits per fruit-producing shoot did not increase. Differences in fruit set among flowers with different phenology and different position within inflorescences persisted also among pollen-supplemented flowers. Furthermore, while pollen availability sometimes may limit fruit initiation, maturation seems to be limited primarily by resources. Genets that received supplementary pollen in 1988 produced fewer flowers in 1989, indicating that long-term fecundity is not necessarily pollen limited. Lastly, exclusion of the main ovary predators increased fruit set.