Abstract
Two-year-old seedlings of Sugi (Japanese cedar: Cryptomeria japonica D. Don) and Hinoki (Japanese cypress: Chamaecyparis obtusa Sieb. et Zucc.) were grown for 4 months in 1/5 Hoagland's No.2 nutrient culture solution containing aluminum chloride in the concentration range of 0.5 to 20 mM within the pH range of 3.5 to 4.0.
Aluminium supplied at or below 1 mM of Al had no effect on the mortality of these species. However, the increase Al concentration higher than 2 mM increased the mortality. While they showed significant growth reduction at or higher Al concentration of 5 mM, there were no difference in growth response to Al between the two species in this experiment.
While Al contents in leaf and root significantly increased with increasing Al concentration in the solution, contents of Ca, Mg and P in leaf decreased. Roof P content in Sugi increased with the increase of Al concentration in the solution, while no such change was observed in Hinoki root. This result suggests that Al migth make phosphate immobile or inviolable form in Sugi root and this might lead to the reduced translocation of P into the leaf. In contrast, Al did not interfere with the uptake of phosphate in the root, however, it might interrupt phosphate transport into leaf from root system in Hinoki.
The Al concentration such as 5 mM in the root sphere induced growth reductions in Sugi and Hinoki, with no significant difference in the response between the two species. This concentration was much higher than those reported in the field crops, vegetables and/or herbs. Thus, if soil acidification will be induced by acidic deposition in future, these herbaceous plants will be influenced faster than the conifer trees. This also means that ground vegetaion change will be observed earlier than the conifer decline by the soil acidification stress.
