Intraseasonal variation in chlorophyll content and chloroplast ultrastructure of selected plant species in a deciduous forest

Abstract

Chlorophyll content and chlorophyll a – chlorophyll b ratios were determined at regular intervals over a 3-month period for eight forest species selected from different levels in a deciduous forest. Chloroplast ultrastructure and starch content were investigated in five of the eight species, chosen to be representative of each level.Chlorophyll a – chlorophyll b ratios for Quercus alba L., Liriodendron tulipifera L., Acer rubrum L., Cornus florida L., Desmodium nudiflorum (L.) DC., and Sassafras albidum (Nuttall) Nees reached a peak at the time of canopy closure whereas total chlorophyll content reached a maximum 1–3 weeks later. The number of thylakoids per granum in all species increased after canopy closure. Chlorophyll content and variations in thylakoid number per granum were found to be related to light intensity variations.Starch content, based on size and number of starch grains, remained stable prior to and after closure in Q. alba, D. nudiflorum, and S. albidum, where a decrease in the number of starch grains was observed after closure. The number of starch grains in D. nudiflorum appeared to decrease during the period 6 weeks after closure. The variations in starch grain number were an indication of photosynthetic activity in these species.The disorganization of grana thylakoids and the development of electron dense and transparent bodies in the chloroplast stroma of all species sampled, 6 weeks after closure, was a preliminary indication of leaf senescence. Electron transparent bodies were considered to be by-products of grana thylakoid degradation.