RESPONSES OF PINUS-PINEA AND P-PINASTER SEEDLING ROOTS TO SUBSTRATA AT DIFFERENT PH VALUES

The behaviour of germinated seeds of Pinus pinea L. and P. pinaster Ai ton, growing in solutions at different pH values, was studied to deter mine the influence of acidity on the root development. Female cones of the two pine species were separately collected during 1989 and 1990 f rom two stations in San Rossore Natural Park (Pisa, Italy). Seeds were germinated up to root lengths of 5 and 10 mm and then transferred to beakers containing either deionized water at pH 5.5 (control) or deion ized water acidified with H2SO4 to pH 4.5 and 3.5; the experiments wer e carried out for 72 hours. Independently of the starting lengths, the elongation rate of seedling roots of both species was significantly d ecreased at pH 3.5. No blocking of mitosis was found; for both species the mitotic index increased between 24 and 48 hours in all media, the n decreased in the roots growing in the control medium and at pH 4.5 a nd significantly increased in those grown at pH 3.5. The lengthening o f root cortex cells was also examined and this was smaller (mean -19%) in roots grown at pH 3.5 than in those growing in the control medium, These results suggest a probable delay or inhibition of the extension phase in the root cell growth.