PARENT SESSION
Poster Session 1: Photosynthesis and Water Relations
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Influence of seed size on seedling establishment at low CO₂.

McCann, Honour¹, Sage, Rowan¹, ¹ University of Toronto, Toronto, Ontario, Canada

ABSTRACT- Seed reserves provide raw materials used by developing seedlings to enhance leaf and root growth, thereby increasing the probability of establishment. Abundant seed reserves should be most valuable where carbon deficiency occurs, for example in shade, and during times of low atmospheric CO₂. Here, we evaluate the hypothesis that low CO₂ conditions favoured genotypes forming large seeds. Five species of Phaseolus were grown in plant growth chambers in a factorial combination of three CO₂ levels (100, 180 and 370 ppm) and three temperature regimes (25/19°C day/night, 30/24°C, 35/29°C). Species were selected to span three orders of magnitude in seed size (ranging from 0.007 to 1.5 g/seed). Seedlings of small-seeded species experienced greater mortality at elevated temperatures and low CO₂ than large-seeded species. At higher CO₂, seedling mortality among all seed-size groups was negligible. At 14 days after germination, production of aboveground biomass and leaf area was measured. Large-seeded species retained proportionately more aboveground biomass and leaf area than small-seeded species. In the treatment providing the greatest level of carbon deficiency (35/29°C, 100 ppm), the smallest-seeded species produced 85% less biomass and 92% less leaf area compared to plants grown at 25°C and 370 ppm CO₂. The largest seeded species produced only 70% less biomass and 78% less leaf area. Our results demonstrate large seed size could provide an adaptive advantage at low CO₂ by allowing plants to avoid mortality and delays in establishment brought on by severe carbon deficiency.

Key words: seed size, seedling establishment, low co2