Three 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 materials. To date, few studies have examined the potential of CT to quantify plant roots in situ. Pre-germinated bean plants were grown for 14 days in PVC containers (10 cm long x 5.0 cm internal diameter) containing a sandy soil medium in a growth chamber under optimum growing conditions. 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 into a 3-D data set for a total rooting depth of 0.8 cm starting at the base of the hypocotyl. This volumetric data set was analyzed for root volume through estimation of relative fractions of root and soil matrix within each voxel for the entire 3-D data set. The rendering of iso-attenuation surfaces illustrated the spatial arrangement of roots with diameters equal and larger than 0.36 mm. In addition, bean root systems were destructively sampled at 1-cm depth increments and analyzed for dry weight, total root length and root diameter. Destructive root sampling 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).