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 forthree-dimensional, nondestructive imaging of heterogeneous materials. Todate, few studies have examined the potential of CT to quantify plant rootsin situ. Pre-germinated bean plants were grown for 14 days in PVC containers(10 cm long×5.0 cm internal diameter) containing a sandy soil medium ina growth chamber under optimum growing conditions. The stems of the beanplants were excised and their root systems imaged with a high-energyindustrial tomography unit (420 kV). Forty individual horizontal tomograms,each 200 μm thick were combined into a 3-D data set for a total rootingdepth of 0.8 cm starting at the base of the hypocotyl. This volumetric dataset was analyzed for root volume through estimation of relative fractions ofroot and soil matrix within each voxel for the entire 3-D data set. Therendering of iso-attenuation surfaces illustrated the spatial arrangement ofroots with diameters equal and larger than 0.36 mm. In addition, bean rootsystems were destructively sampled at 1-cm depth increments and analyzed fordry weight, total root length and root diameter. Destructive root samplingyielded a root length per unit volume (Lv) between 44 and 60 cm cm-3soil, whereas the CT-measured Lv was about 76 cm cm-3.