LE3 .A278 2011

2011

Reekie, Edward

Acadia University

Bachelor of Science

Honours

Biology

Biology

The effect of light on seedling de-etiolation and elongation has been well documented. Etiolated seedlings use their seed reserves to elongate rapidly in order to reach the surface of the soil where light is available for photosynthesis. In addition to a change in light availability, seedlings are also exposed to a carbon dioxide gradient. Deep within soil, root and microorganism respiration cause a carbon dioxide efflux. As a seedling reaches the litter layer, the carbon dioxide concentration decreases, and continues to decrease to atmospheric levels above the litter layer. Although this decrease in CO2 concentration could be used by seedlings as a developmental signal to help control the etiolation response, little is known regarding the possible effect of CO2 on etiolation. I examined the effect of carbon dioxide on seedling elongation in 17 species of trees and shrubs of varying seed size. Plants received 4h d-1 of light at an irradiance of 2.5 μmol m-2 s-1 for a total of 7 days. Seedling elongation was examined at four different carbon dioxide levels: 0, 380, 760 and 1520 μmol•mol-1. Generally, species with smaller seed sizes responded positively to an increase in carbon dioxide in terms of height, while species with larger seeds responded negatively. Small seeded species need to reach the surface of the soil before their limited seed reserves are depleted. This may explain the positive height response of species with small seeds to elevated carbon dioxide. Previous studies have shown that photosynthesis in species with large seeds responds more positively to elevated carbon dioxide than in small seeded species. When light is available, it may be more beneficial for larger seeded species to remain under the litter layer, where the carbon dioxide concentration is higher.

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