Temperature and time-related variation of root growth in some conifer tree species

Abstract

The variability of root growth potential of cold-stored (2 °C) bare-root and container-grown stock of Abiesgrandis (Dougl.) Lindl., A. amabilis (Dougl.) Forbes., Piceasitchensis (Bong.) Carr., Pseudotsugamenziesii (Mirb.) Franco, Thujaplicata Donn, and Tsugaheterophylla (Raf.) Sarg. was tested under four air temperature regimes for 7 and 14 days. In P. menziesii, P. sitchensis, and T. plicata, root growth was greatest under the 25:20 °C (light:dark) regime, whereas the 30:25 °C (light:dark) regime was supraoptimal for all species. Temperatures cooler than 25:20 °C (light:dark) were optimal for T. heterophylla and A. amabilis. A 14-day test duration consistently produced more roots than the 7-day test. Container-grown seedlings produced more new roots than bare-root seedlings. Except for P. sitchensis and T. plicata, light was required for root growth. The effect of test conditions on root growth is discussed with respect to a possible relationship between temperature optima for root growth and current photosynthate production. High within-test variability and inconsistent ranking of seed lots under different test temperatures and durations suggest that stock quality interpretations based solely on root growth potential tests should be questioned.