Effects of humic acid derived from sediments on growth, photosynthesis and chloroplast ultrastructure in chrysanthemum

Humic acid (HA) is natural biological organic fertilizer derived from organic waste materials, which shows a highly promoting effect on plant growth and development. However, the mechanisms responsible for the promoting effect of humic acid on the growth and development are poorly understood. In this study, the physiological mechanisms of foliar humic acid (FHA) fertilizer on chrysanthemum growth and development from the viewpoint of photosynthesis and chloroplast ultrastructure were investigated. Seedlings of chrysanthemum were sprayed with the same volume of distilled H2O (control), inorganic NPK fertilizer and organic foliar humic acid fertilizer every 15 days (15, 30, 45, 60 days after transplanting). The results showed that the morphologital indices (stem diameter, fresh weights of shoots and roots, the root to shoot ratios, dry weights of shoots and roots, leaf area, flower diameter), the net photosynthesis rate, the chlorophyll fluorescence, the content of chlorophyll and the chloroplast ultrastructure of chrysanthemum improved obviously after foliar application of humic acid compared with those of the control and the NPK fertilizer. The promoting effect of the humic acid fertilizer showed an obvious dose-effect. The results from correlation analysis indicated that the responses of the foliar humic acid fertilizer on growth and development of chrysanthemum could be related with a constitutive increased net photosynthetic rate due to the high content of chlorophyll and the improved chloroplast ultrastructure. (C) 2014 Published by Elsevier B.V.