Physiological, morphological, and anatomical changes in Rhododendron agastum in response to shading

Abstract

To investigate how shading intensity influences azalea (Rhododendron agastum) seedlings, we examined changes in plant growth (both anatomical and physiological). For this, Rh. agastum plants were grown under different shading intensities: 0, 31.28, 52.07, and 86.35 %. The results showed that the height, leaf areas and chlorophyll content increased under shade, whereas ground diameter and root length decreased under shade, which caused an increase in the height/diameter ratio. We found that 31.28 % shading significantly enhanced the biomass accumulation, net photosynthetic rate and the light-saturation point. Shading also altered the anatomic structure of Rh. agastum leaves, including reductions in leaf thickness, stomatal density, stomatal indices, and the thickness of the palisade tissue and the number of cellular layers therein, increased in the lengths of the vertical and lateral axes, and the ratio of palisade tissue to spongy tissue was reduced, which were beneficial to transpiration and photosynthesis. Therefore, the anatomic structure and the photosynthesis characteristics of Rh. agastum were closely connected. On the basis of these results, it could be deduced that moderate shading induces a physiological adaptation mechanism, which markedly affects the form and photosynthesis thereof.