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

Exposure to full sun provided the most stressful environment, as reflected by foliar characteris-tics, 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. Incomparison with shaded plants, foliar chemical concentrations (as percentage dry weight) weregreatly reduced, unit-area concentrations were greatly increased, total leaf area per plant wasreduced about half, and average leaf areas and specific blade areas were greatly reduced. Exposedplants also lacked almost totally the normal fourth age class of foliage.
Reduced temperatures and growing-season length, associated with shaded sites at high eleva-tion, caused intermediate levels of stress. This was indicated by intermediate unit-area measure-ments of foliar chemical concentrations, total leaf area per plant, average leaf size, and specificblade area. Percentage dry weight concentrations did not differ significantly from those of othershaded plants. Foliar biomass per plant was similar for the high-elevation site and the exposedsite. Woody biomass of shaded plants at high elevations was similar to that of shaded plants at lowelevations.
Results showed that the dimensional characteristics of leaves (average leaf area, specific bladearea), the total leaf area per plant, and foliar chemical concentrations expressed on a unit-areabasis were the foliar characteristics most accurately reflecting stressful environments.