Influence de l'intensité lumineuse, de la température nocturne de l'air et de la concentration en CO2 sur la croissance de semis d'épinette noire (Piceamariana) produits en récipients en serres

Growth of containerized black spruce seedlings grown in greenhouses was studied in relation to factors known to influence plant growth. Artificial light intensity (3.80 and 72.04 μmol•m−2•s−1) and night air temperature (5, 10, 12.5, 15, and 20 °C) were considered in a first experiment and artificial light intensity (4.24 and 59.57 μmol•m−2•s−1) and CO2 air concentration (ambient and 1000 μL•L−1) in a second one. Higher light intensity and CO2 enrichment increased dry biomass of seedlings as well as growth in height and stem diameter. Both factors similarly enhanced the last two parameters since height/diameter ratios showed little variation among treatments. Reducing night air temperature down to 10 °C did not significantly influence height growth nor biomass increase when high intensity light was provided. Lower light intensity raised the threshold to 12.5 °C. Shoot height, diameter, and dry biomass as well as the number of branches and buds per millimeter were strongly reduced by a 5 °C night air temperature. High intensity light enhanced growth of containerized black spruce seedlings more than CO2 enrichment or a 5 °C night air temperature. When used simultaneously, these growth enhancing factors had a synergistic effect during most of the treatment period; thereafter, the effect became partially additive. The relative growth rate peaked at the onset of exponential shoot growth and decreased after this point. However, the enhancing factors were still efficient since absolute growth differences between seedlings grown under the most favorable conditions and controls kept increasing. The faster growing pace imposed by these growth enhancing conditions during the treatment period was maintained over the entire first growing season.