Photosynthesis and dark respiration of black spruce cuttings during rooting in response to light and temperature

Abstract

Photosynthesis and dark respiration of semihardened black spruce cuttings (Piceamariana (Mill.) B.S.P.) were periodically measured at a range of light intensities at 10, 15, 20, 25, and 30 °C over an 8-week period in rooting chambers and for 4 additional weeks after the cuttings were transferred to a greenhouse. Increases in the total dry weight of the cuttings over the experimental period were due exclusively to increases in root biomass. The light-saturated photosynthetic rates at 20 °C decreased from 3.8 to 2.2 μmol CO2•m−2•s−1 during the 8 weeks in the rooting chamber. At 15 °C, the light-saturated photosynthetic rate was about 2 μmol CO2•m−2•s−1 and no significant change was observed during the experimental period. Maximum photosynthetic rates were generally attained at photosynthetic photon flux densities (PPFD) of 200–300 μmol•m−2•s−1 At the range of PPFD generally used in rooting chambers (0–50 μmol•m−2•s−1), the light use efficiency of cuttings (net photosynthesis per cutting per PPFD) was greatest at 15 °C. Furthermore, the light compensation point was lowest at 15 °C. The effect of light intensity and temperature on the photosynthesis and dark respiration of cuttings was modelled to predict the carbon balance of cuttings under different conditions of PPFD and temperature. This model should be useful in determining an appropriate set of environmental conditions to use inside rooting chambers and thus improve the overall physiological quality of this type of vegetatively propagated planting stock. The modelling approach described in this study could prove useful for the production of other conifer species by rooted cuttings even when it is conducted using other methods of cultivation (e.g., cold-frames or greenhouses).