NONINVASIVE STUDIES OF CONIFER ROOTS - NUCLEAR-MAGNETIC-RESONANCE (NMR) IMAGING OF DOUGLAS-FIR SEEDLINGS

An artificial soil mix suitable for magnetic resonance imaging was developed. This soil mix, consisting of quartz sand, peat moss, and kaolinite clay (5:3:2, by volume), has a natural texture and consistence and produces high-contrast images in soil media with up to 15% water content. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown in this soil mix in 12.5 cm diameter containers and periodically imaged over a 12-month period. These images showed roots growing undisturbed in the soil mix and initiation of numerous lateral roots. From these images, root lengths and growth rates were calculated. Calculated root lengths were in close agreement with measured lengths of excavated roots. Undisturbed lateral roots had measured growth rates of about 1 mm/day. Roots that reached the container wall and then grew down along the wall had significantly higher growth rates, over 2 mm/day. This phenomenon may have important implications for growth rate data from root window and minirhizotron experiments.