1976 Volume 39 Issue 4 Pages 16-21
Resistance of the garden trees and shrubs against SO2 is determined, not only by the hereditary nature of the plants themselves, but by environmental conditions in which they are placed. Especially, the increasingly poor nutrient conditions of the urban environments are supposed to affect the resistance of the garden trees and shrubs. This research was made for the purpose of experimentally clarifying how poor nutrient conditions, especially the lack of nitrogen, phosphorus, and potassium, affect the resistance of trees and shrubs, thus hoping to help in any way in the technical progress of the upkeeping of garden trees and shrubs in the treeplanting tasks in cities.
The following trees were used as samples of the garden plants:
Raphiolepis umbellata Makino var. minor Makino (Himesharinbai)
Euonymus japonicus Thunb.(Masaki)
Viburnum awabuki K. Koch (Sangoju)
The sample trees were planted in sand beds prepared with different nutrient conditions for 30 days. Then they were put in growth cabinets for pollution test and contaminated with 3 ppm of SO2 under a fi xed (20°C) temperature for 3 hours. Then their damages were observed. Color of leaves, as well as amounts of nitrogen and potassium contained in them were measured. Experiments were made twice during the year, once in summer (August 31st) and once in winter (December 2nd), and the seasonal changes of the results were checked. The sand beds were made by Hoagland and Arnon solution, and fi ve sections were made with different nutrient conditions: complete nutrients (nitrogen, phosphorus, and potassium) section, potassium deficiency section, phosphorus deficiency section, nitrogen deficiency section, and a section with no nutrients. The results of the experiments were as follows:
1) The differences made on the resistance against SO2 by the various nutrient conditions were generally great in the summer season. After the contamination by SOs, damages of the trees grown in no-nutrient section were the greatest. Those grown in nitrogen deficiency section were the next worse in their damage. On the other hand, trees grown in the complete nutrients section had the least damages, and those in potassium deficiency section showed also comparatively small damages. As long as this experiment is concerned, the lack of nitrogen greatly affects the resistance against SO2, and the lack of potassium affects lightly. In winter similar results, though in much slighter degrees, were observed, but they were hardly considered as damages. Practically no differences made by various nutrient conditions were recognizable.
2) The falling of leaves is considered to be one index of the damage. The falling leaves during the summer season of Himesharinbai and Sangoju showed the same trend with their other damages.
3) Observation of the color of leaves showed that the damaged leaves had greater lightness, with red of yellowish shade in it. No recognizable features were observed in the variation of the color differences caused by the lack of nutrients.
4) An analysis of the components of leaves showed that the leaves of trees grown in nitrogen deficiency section, potassium deficiency section, and no nutrient section lacked nitrogen, potassium, and the both respectively, in comparison with other sections.
5) As for the resistance against SO2 of each of the sample trees, the expeiments showed that Masaki had the strongest, next Himesharinbai, and the damages were greatest in Sangoju.
