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 wa s immersed individually for 10 sec in 0.05 M, 0.10 M and 0.15 M aqueou s NaNO2 solution and the excess solution on the root surface allowed t o drain off. It was then transferred to conical flask containing disti lled water and shaken for 15 min for desorption of nitrite. A known qu antity of this aliquot was reacted with 1% acidic sulphanilamide and 0 .02% NED HCl. A pink colour developed, and its optical density was rea d at 540 nm. A positive linear correlation was noted between colour de nsity and root surface area. The respective correlation coefficient va lues for 0.05 M, 0.10 M and 0.15 M NaNO2 solutions were 0.973, 0.963 a nd 0.964 for Acacia catechu, 0.933, 0.903 and 0.898 for Eucalyptus cam aldulensis and 0.968, 0.976 and 0.972 for Leucaena leucocephala (signi ficant at p < 0.001). The method was successfully adopted to determine the root surface area of seedlings of Albizia lebbek, A. procera, Aca cia auriculiformis, A. nilotica, Dalbergia latifolia and D. sissoo.