Hardware and software efficacy in assessment of fine root diameter distributions

Fine roots constitute the majority of root system surface area and thus most of the nutrient and water absorption surface. Fine roots are, however, the least understood of all plant roots. A sensitivity analysis of several software programs capable of providing root diameter distribution analyses was undertaken to determine if this software was capable of discriminating 10% changes in diameters of roots in the 0.05–0.2 mm diameter range. Digital images produced by drawing discrete lines, by scanning wires of various diameters, and by scanning roots from several legume species were analyzed and compared. None of the three packages were able to adequately analyze these images. Each introduced artifacts into the data that were severe enough to confound interpretation of the resulting diameter class length histograms at resolutions from 24 to 400 pixels (px) mm⁻¹, and root diameters from 0.06 to 0.5 mm or larger. One package was, however, clearly superior to the other two for routine digital analysis. All three packages require additional development before they are suitable for routine analysis of fine roots. Due to the 252 px mm⁻¹ resolution ceiling with currently available scanners, the smallest roots for which this level of discrimination is possible is 0.12 mm diameter. For many agricultural and forest species, up to 95% of their total root length is less than 0.1 mm in diameter. It is concluded that both hardware and software constraints currently inhibit the sensitivity of investigations into fine root diameter shifts in response to environmental conditions.