PARENT SESSION
Poster Session #35: Reproductive Ecology.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Interactive effects of plant age and nitrogen supply on reproductive allocation in Ipomoea nil.

Tom, Jessica^*,1, Lewis, James², ¹ Pleasantville High School, Pleasantville, New York² Fordham University, Armonk, New York

ABSTRACT- Reproductive output in annual plants generally increases with increasing plant size. However, changes in resource availability and the length of the vegetative growth phase may significantly alter reproductive output through effects on both the absolute and relative allocation of biomass to reproductive structures. In this study, we examined the interactive effects of plant age and nitrogen supply on allocation to reproduction in the determinate, short-day, annual species Ipomoea nil (syn. Pharbitis nil) cv. Scarlett O′Hara (morning glory). Four cohorts of plants were planted at ten-day intervals in a greenhouse. Five plants in each cohort were given one of four nitrogen treatments (0.1, 0.5, 1.0, 5.0 mM NH₄NO₃). Supplemental lighting was used to maintain an 18 h photoperiod during vegetative growth. All plants were simultaneously induced to flower by switching the photoperiod to 12 h. All plants were harvested 74 d after the induction of flowering. Reproductive and total plant mass was highest in the second cohort, associated with senescence in the first cohort and shorter vegetative growth periods for cohorts 3 and 4. Although absolute allocation to reproduction increased with increasing plant size and nitrogen supply, relative allocation did not significantly vary with plant size. There generally were no significant interactions between plant age and nitrogen supply on growth or allocation parameters. These results suggest that there is an optimal time for flowering to maximize reproductive output in Ipomoea nil. Additionally, these results suggest that plant age and nitrogen supply do not significantly affect the allometric relationship between reproductive and total living biomass in Ipomoea nil.

KEY WORDS: Ipomoea nil, allometric relationships, reproductive output, timing of germination