Ion exchange reactions on the stem surface of Chamaecyparis obtusa Sieb. et Zucc.

Abstract

In order to clarify the sources of soil acidification below stands of hinoki (Chamecyparis obtusa Sieb. et Zucc.), artificial stemflow experiments were performed to separate out the role rainfall acidity has from that of the acidity potentially occurring during stemflow. Various solutions, including distilled water, NaCl, NH 4 Cl, KCl and CaCl 2 +MgCl 2 solutions, were added in a controlled manner to the upper stem and the solutions systematically collected at breast height. Although the original pH values of the salt solutions were around 5.5, the pH values of stemflow ranged from 3.8 to 4.2. The ion balance [anion (including bicarbonate ions) to cation concentration] decreased with initial stemflow but recovered after ca. 5 l of flow. At this point, pH values continued to decrease and this decrease was accompanied by a decrease in the cation concentration of the stemflow. These results indicate that there are two ways by which stemflow can be acidified. In the initial stage of flow, organic and inorganic acids are dissolved in the stemflow. Following this, ion exchange occurs between cations contained in the stemflow and hydrogen ions adsorbed in the stem. The last step appears most critical in the acidification process. Materials and methodsExperiments were performed in the Mie Prefecture Forestry Research Institute's experimental forest (34°40′N, 138°20′E; altitude: ca. 230 m) in central Japan. A 12-m tower was built in a 31-yearold hinoki (Chamaecyparis obtusa Sieb. et Zucc.) plantation. Two

Literature review of stemflow generation and chemical characteristics in Japanese forests

“…The authors concluded that the strong acidity of Japanese cedar was controlled by organic acid supplied from the vegetation, atmospheric SO4 2deposition and partly neutralized by leaching of cations (K + , Ca 2+ , and Mg 2+ ). This mechanism is similar to the stemflow studies of other tree species reported by Fan et al (1999) and Takenaka and Sasama (2000).…”

“…As a general rule, stemflow pH values for coniferous species are lower than for hardwood species (Takenaka and Sasama, 2000). In particular, IKAWA…”

“…Cl - Takenaka and Sasama (2000) 3.0-3.9 3.5-4.1 4.2-4.8 4.5-5.2 5.0-6.0 5.2-5.9 5.9-6.5 Japanese cypress (C. obtusa) tends to have a higher acidity than other tree species (Sassa et al, 1991;Takenaka and Sasama, 2000). Furthermore, these pH values are lower than the average pH (4.8) value of rainwater in Japan (Table 2) there was no significant difference in the throughfall pH from the two forest stands, however, the stemflow pH of C. japonica was significantly lower than that of P. ediulis.…”

“…Japanese cypress (C. obtusa) also has a highly acidic stemflow. Takenaka and Sasama (2000) performed The last step appears to be the most critical in the acidification process. The formation mechanism for pH of stemflow is clarified in these studies.…”