Root system responses of Japanese red cedar saplings to acidic conditions

Stemflow From Japanese red cedar (Cryptomeria japonica) enters forest soil at a low pH. We evaluated the responses of the root system of Japanese red cedar saplings to acidic conditions, used to simulate this situation, in tw o different growth media, a brown forest soil (BS) and a Yahagi sand (YS). Soils were acidified by the addition of solutions at pH 2.0, 3.0 and 5.5 (c ontrol). Root morphology, root surface area index, root respiration activit y and root biomass were measured. In the pH 3.0 treatment, no significant e ffects were found on the root systems compared with the controls in either soil, except for a slight difference in root-tip diameter in the Yahagi san d. In the pH 2.0 treatment, the surface area index and dry weight ratios of the whole root in the Yahagi sand were significantly lower than those in t he other treatments. No significant effects on the whole root were observed in the brown forest soil. These results suggest that detrimental effects o f acidic solutions on the root systems would be less significant in brown f orest soil, which contains humus, than in the Yahagi sand, which lacks humu s. They also suggest that the threshold pH value causing visible morphologi cal changes on the roots of Japanese red cedar saplings falls in the pH ran ge between 2 and 3. White roots in the pH 2.0 treatment had low respiration activity and showed visible morphological changes in both soils. These res ponses were presumably related to the effects of excess Al in the soil solu tion. White roots in the pH 2.0 treatment typically produced exodermis. The results suggest that stemflow with a pH of 3.0 has no effects on the root systems of Japanese red cedar, and that the morphology of white roots was a dversely affected not by treatment at pH 2.0 but by excess water-soluble Al in the soil. (C) 2000 Elsevier Science B.V. All rights reserved.