PARENT SESSION
Poster Session #11: Elevated CO₂.
Monday, August 6, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Interactive effects of plant age and elevated CO₂ partial pressures on reproductive allocation in a developmentally-determinate plant.

Lewis, James¹, Wang, Xianzhong², Griffin, Kevin², Tissue, David³, ^{1 2 3}

ABSTRACT- Increasing atmospheric CO₂ partial pressures may alter biomass allocation to reproductive structures through changes in both absolute and relative allocation. Plant age may also alter the absolute and relative allocation of biomass to reproductive structures. In this study, we used a novel experimental protocol to examine the interactive effects of elevated CO₂ partial pressures and plant age on allocation to reproduction in the determinate, short-day species Xanthium strumarium (common cocklebur). Six cohorts of plants were planted at five-day intervals in chambers maintained at either 36.5 or 73.0 Pa CO₂, with an 18 h photoperiod and a non-limiting nutrient supply. All plants were induced to flower simultaneously by switching the photoperiod to 12 h for two days, then switching back to an 18 h photoperiod for the remainder of the experiment. All plants were harvested 10 d after the onset of fruit production. Total plant mass significantly increased with increasing CO₂ partial pressure and with increasing plant age. In contrast, fruit mass significantly decreased with increasing plant age and was not significantly affected by CO₂ supply. These results were due to a significant reduction in the relative allocation of biomass to fruit with increasing plant age and increasing CO₂ partial pressure. There were no significant interactions between plant age and CO₂ treatment. These results suggest that increasing atmospheric CO₂ may not increase fruit production in Xanthium.

KEY WORDS: development, elevated CO₂, reproductive allocation, Xanthium strumarium