3-DIMENSIONAL IMAGING OF PLANT-ROOTS IN-SITU WITH X-RAY COMPUTED-TOMOGRAPHY

X-ray Computed Tomography (CT) is a non-invasive technique that allows for three-dimensional, nondestructive imaging of heterogeneous materi als. To date, few studies have examined the potential of CT to quantif y plant roots in situ. Pre-germinated bean plants were grown for 14 da ys in PVC containers (10 cm long x 5.0 cm internal diameter) containin g a sandy soil medium in a growth chamber under optimum growing condit ions. The stems of the bean plants were excised and their root systems imaged with a high-energy industrial tomography unit (420 kV). Forty individual horizontal tomograms, each 200 mu m thick were combined int o a 3-D data set for a total rooting depth of 0.8 cm starting at the b ase of the hypocotyl. This volumetric data set was analyzed for root v olume through estimation of relative fractions of root and soil matrix within each voxel for the entire 3-D data set. The rendering of iso-a ttenuation surfaces illustrated the spatial arrangement of roots with diameters equal and larger than 0.36 mm. In addition, bean root system s were destructively sampled at 1-cm depth increments and analyzed for dry weight, total root length and root diameter. Destructive root sam pling yielded a root length per unit volume (L-v) between 44 and 60 cm cm(-3) soil, whereas the CT-measured L-v was about 76 cm cm(-3).