Assessing stress in Rhododendron macrophyllum through an analysis of leaf physical and chemical characteristics

Abstract

Exposure to full sun provided the most stressful environment, as reflected by foliar characteristics, for naturally occurring Rhododendron macrophyllum growing at low to middle elevations. However, for a given age, exposed plants had a greater woody biomass than shaded plants. In comparison with shaded plants, foliar chemical concentrations (as percentage dry weight) were greatly reduced, unit-area concentrations were greatly increased, total leaf area per plant was reduced about half, and average leaf areas and specific blade areas were greatly reduced. Exposed plants also lacked almost totally the normal fourth age class of foliage.Reduced temperatures and growing-season length, associated with shaded sites at high elevation, caused intermediate levels of stress. This was indicated by intermediate unit-area measurements of foliar chemical concentrations, total leaf area per plant, average leaf size, and specific blade area. Percentage dry weight concentrations did not differ significantly from those of other shaded plants. Foliar biomass per plant was similar for the high-elevation site and the exposed site. Woody biomass of shaded plants at high elevations was similar to that of shaded plants at low elevations.Results showed that the dimensional characteristics of leaves (average leaf area, specific blade area), the total leaf area per plant, and foliar chemical concentrations expressed on a unit-area basis were the foliar characteristics most accurately reflecting stressful environments.