Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 2007
Publication Date: August 1, 2007
Citation: Zobel, R.W., Baligar, V.C., Kinraide, T.B. 2007. Fine root diameters can change in response to changes in nutrient concentrations. Plant and Soil Journal. 297:243-254.
Interpretive Summary: Increasing reliance on marginal land to produce the food needed for an expanding world population requires knowledge of plant mechanisms for adapting to problem soils. The finest roots of plants are the primary sites of nutrient and water uptake, but their development and functioning are not thoroughly understood. This paper explores the adaptation of fine roots to changes in available nutrients, showing that the roots become thinner or thicker in response to nutrient changes. It is shown that this response occurs in different patterns in a diversity of species. The author concludes that current technology can only barely measure these changes in root thickness.
The dynamic adaptation of roots to changes in soil chemistry, including nutrients, has been only cursorily explored. Specific Root Length, though an easily measured characteristic of root adaptation/functionality, is compromised by changes in root mass density and diameter in addition to changes in root length. Four species, of Theobroma cacao L. (Cacao), Triticum aestivum L. cv Scout. (Wheat), Aeschynomene indica L. (Jointvetch) and Vigna juruana (Harms) Verdc. (Tropical Cowpea) were grown in hydroponics and subjected to a range of nitrate, Phosphorus, Aluminum, or Tannic acid concentrations. Images of the roots made on a scanner at several pixel densities (24, 47, 94, or 252 p mm-1 - 600, 1200, 2400, and 6400 dpi respectively) were assessed for root diameter with WinRhizo root measuring software. Cacao roots responded to increasing nitrate concentrations by becoming thinner (from 0.18 mm to 0.14 mm diameter); Jointvetch roots became thicker with reduced phosphorus (from 0.14 to 0.18 mm diameter); Cowpea roots did not change in length or diameter with reduced phosphorus; Wheat roots became thicker with increasing concentrations of both Aluminum and Tannic acid (from 0.28 to 0.36 mm and 0.28 to 0.44 mm respectively). Using drawn lines, it was demonstrated that part of the extensive "noise" in WinRhizo and Delta-T scan data is due to artifacts introduced by the analysis. It is concluded that pixel resolutions, in excess of 100 p mm-1, are needed to document fine root responses to nutrient shifts, and that existing technology requires additional development efforts to be fully efficacious.