Leakage of UV‐absorbing substances as a measure of salt injury in leaf tissue of woody species

Leakage of UV‐absorbing substances from leaf discs was used to determine salt and osmotic injury after treatment. A relative leakage ratio was calculated by dividing the UV absorption after treatment by the total absorption obtained after freeze‐killing the tissue. Time‐course results using Populus tremuloides Michx. leaves indicated 24 h as an appropriate treatment duration. NaCl and KCl caused more leakage than Na 2 SO 4 and K 2 SO 4 in P. tremuloides and Fraxinus pennsylvanica Marsh, the most sensitive species tested. Amelanchier alnifolia (Nutt.) Nutt. ex Roem. was more sensitive to K 2 SO 4 than to KCl. Elaeagnus angustifolia L. and Caragana arborescens Lm. were the most tolerant to both salts. Tolerance to salts was greater in August than earlier in the growing season. Treatment of leaves with solutions of sucrose, PEG‐8000 and mannitol iso‐osmotic with KCl and NaCl showed that increased leakage was caused by specific ion effects, rather than osmotic effects.