PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Short-term exposure to elevated CO₂ causes downwards regulation of photosynthesis in black spruce seedlings. Danielle Way^*,1, Rowan Sage¹, ¹ Department of Botany, Toronto, Ontario, Canada

ABSTRACT- Short-term exposure to elevated CO₂ (carbon loading) may be useful for building carbohydrate reserves in nursery-grown tree seedlings; carbohydrate reserves could help increase stress tolerance after seedlings are planted in the field. However, the small potting volumes used in tree nurseries may cause downwards regulation of photosynthesis, thereby reducing carbohydrate accumulation. High nutrient availability, such as with an enriched fertilization regime, may prevent downwards regulation of photosynthesis, allowing for effective carbon loading even with small pot volumes. Black spruce seedlings (Picea mariana (Mill.) B.S.P.) were exposed to either ambient (375 mol mol^-1) or elevated (1000 mol mol^-1) CO₂ levels, and either a conventional or exponential nutrient loading fertilization regime at the end of their first growing season. Seedlings were grown under greenhouse conditions and placed in CO₂ chambers for 24 days. Seedlings exposed to elevated CO₂ showed strong downwards regulation of photosynthesis within 16 days; net rates of CO₂ assimilation of ambient and elevated CO₂ treatments were identical after 24 days of exposure. Fertilization treatment had no effect on net CO₂ assimilation rates. Carbon loading also increased seedling biomass. The downwards regulation of photosynthesis was likely due to the small potting volume used by commercial nurseries for seedlings, limiting the usefulness of carbon loading as a technique in these conditions.

KEY WORDS: spruce, photosynthetic acclimation