Effects of light intensity on physio-biochemical characteristics of Chrysanthemum indicum

Abstract

By analyzing the effects of light intensity on the growth, physiological and biochemical characteristics of Chrysanthemum indicum, the light intensity suitable for the growth of Ch. indicum was revealed, which provided a reference for the planting of Ch. indicum. There were five treatment groups of Ch. indicum, which was planted under 100%, 80%, 60%, 40% and 20% all natural light intensity conditions, respectively. In the meantime, these indicators of photosynthetic physiology, such as relative growth, photosynthetic pigment content, photosynthetic parameters, and chlorophyll fluorescence parameters etc. were measured in the peak period of growth of Ch. indicum as well as related indicators of the protective enzyme system, and the ultrastructure of chloroplast was observed with the use of transmission electron microscope technique. In our study, the results showed that the leaves of Ch. indicum occurred yellow phenomenon in different degrees when Ch. indicum was placed at more than 80% of the total natural light intensity condition, the height and stem diameter of plant reached the maximum at 60% of the total natural light intensity. More importantly, the number of branches of Ch. indicum was significantly increased under the total natural light intensity of more than 60%. Both the content of photosynthetic pigment and net photosynthetic rate were negatively correlated with light intensity, while photosynthetic parameters and chlorophyll fluorescence parameters showed a trend of rising first and then decreasing with the decrease of light intensity. The physiological indexes of Ch.indicum including stomatal conductivity, intracellular CO_2 concentration, transpiration rate, water use efficiency and actual photochemical quantum yield of PS Ⅱ had been determined, and the results showed that all of them were at the highest level under 60% total natural light intensity condition. The chloroplast structure of Ch. indicum was not obviously abnormal under 60% and 80% total natural light intensity treatments, but the stroma lamella was broken under 100% total natural light intensity, and not only the number of chloroplast, but also the number and volume of starch grains were decreased significantly under 20% and 40% total natural light intensity. With the decrease of light intensity, the enzymes activities of SOD and CAT decreased, the activity of POD increased in the early stage and decreased in the later stage, and the content of MDA showed a decreasing trend. The analysis of results indicated that the Ch. indicum can grow under 20%-100% total natural light intensity, but the best growth condition was under 60% total natural light intensity.