To determine the effect of Al on the growth of P- or Ca-deficient woody plants, 2-month-old Quercus acutissima Carr. seedlings were preliminarily cultured at pH 5.8 for 9 weeks in one of three hydroponic culture media: (A) 1/5 Hoagland medium containing complete nutrients; (B) 1/5 Hoagland medium without P; or (C) 1/5 Hoagland medium without Ca. Seedlings from each medium were then transplanted to medium containing either 0, 0.27, or 2.7 mM Al with the same nutrient conditions as the preliminary cultivation, and cultured at pH 4.0 for 6 more weeks. The seedlings were then harvested, the dry weights of plant parts were determined, and the Al, Ca and P contents in each plant part were analyzed. In the Ca-deficient medium without Al, the rate of root elongation declined within 9 weeks. However, the dry weight of new roots significantly increased after 6 weeks in the solution without Ca but with 2.7 mM Al. The biomass of both shoots and roots was low in the P-deficient medium containing 2.7 mM Al. With 2.7 mM Al, high levels of Al were detected in roots and leaves. These results indicate that the presence of P is essential for characteristic root development following Al exposure.
In order to clarify the relationship between leaf SPAD value and vitality of street tree, we compared leaf physiological properties among trees of Zelkova serrata Makino. There were two types of the planted condition; concrete-paved and bare soil around the planting pits. We classified Z. serrata trees into three vitality categories as follows: healthy, unhealthy and declined according to leaf SPAD value. Many trees, which planted in concrete pavement, classified into unhealthy or declined. We also measured leaf water potential, transpiration rate, photosynthetic rate and chlorophyll fluorescence (Fv/Fm) to clarify the physiological status of trees in each group. The healthy and unhealthy trees showed higher pre-dawn leaf water potential and higher diurnal transpiration rate than declined trees. In addition, the declined trees showed lower Fv/Fm in midday. Therefore, the declined trees may suffer from drought stress and strong light stress by their planted condition. In this study, diagnostic method based on SPAD value considered useful to evaluate the vitality of Z. serrata trees.
We found a Pinus densiflora canopy tree where the eggs had been deposited by the Japanese pine sawyer Monochamus alternatus in a coastal pine forest in Akita, October 2006. The tree exhibited no external symptoms of the pine wilt disease at that time. As discolored tree crown is an important cue to find diseased trees, we recorded the change in the crown coloration until June 2007 and then the trunk was cut into 1-m-long logs and placed in an outdoor cage to collect M. alternatus adults. The tree crown remained green and the needles were not withered (i.e. apparently healthy). No ability of oleoresin exudation on the trunk up to 4 m above the ground, indicated that the tree was weakened by the following June. Four of the 11 M. alternatus adults emerged from the caged logs in summer 2007, carried Bursaphelenchus xylophilus. An adult beetle carried 18,100 B. xylophilus, and the others < 100 nematodes individually.