ROOT SURFACE-AREA MEASUREMENTS BASED ON ADSORPTION AND DESORPTION OF NITRITE

A method, based on the negative adsorption of NO2- has been developed to determine surface area of roots. Young roots of 3-4 year old plants of Acacia catechu, Eucalyptus camaldulensis and Leucaena leucocephala were up-rooted and cut into 18 cylindrical pieces. Each root piece was immersed individually for 10 sec in 0.05 M, 0.10 M and 0.15 M aqueous NaNO2 solution and the excess solution on the root surface allowed to drain off. It was then transferred to conical flask containing distilled water and shaken for 15 min for desorption of nitrite. A known quantity of this aliquot was reacted with 1% acidic sulphanilamide and 0.02% NED HCl. A pink colour developed, and its optical density was read at 540 nm. A positive linear correlation was noted between colour density and root surface area. The respective correlation coefficient values for 0.05 M, 0.10 M and 0.15 M NaNO2 solutions were 0.973, 0.963 and 0.964 for Acacia catechu, 0.933, 0.903 and 0.898 for Eucalyptus camaldulensis and 0.968, 0.976 and 0.972 for Leucaena leucocephala (significant at p < 0.001). The method was successfully adopted to determine the root surface area of seedlings of Albizia lebbek, A. procera, Acacia auriculiformis, A. nilotica, Dalbergia latifolia and D. sissoo.