PH distribution in radial sections of the stem and root of Cryptomeriajaponica

Abstract

The pH distribution in the outer bark, inner bark, cambium, and xylem layer of a conifer, Cryptomeriajaponica, was measured using an iridium oxide electrode and a flat-type glass electrode. The outer bark of C. japonica was strongly acidic, and there was a difference in pH between the outer and inner bark. The outer bark had a pH of about 3 from the surface to the inside. The inner bark pH was about 4 at the outer bark side and about 6 near the cambium side. The pH was maximal (about 6.3) in the cambium, and slightly lower in the outer xylem. pH values determined in subsections of the outer bark after chemical washing with pure water, hydrochloric acid, barium chloride, and formic acid suggested that water-insoluble carboxyl (—COOH) groups bound to organic polymers contribute to the strong acidity of the outer bark.