Effects Of Humic Acid On The Photosynthesis, Chloroplast Ultrastructure And Vase Life In Chrysanthemum

Humic acid(HA) is natural biological organic fertilizer derived from organic waste materials. In this study, the effects of foliar humic acid(FHA) fertilizer, compared with water and NPK fertilizer, on the growth, development and postharvest vase life of chrysanthemum(C. morifolium cv. ‘Jinba’) were investigated. In order to provide theoretical basis for the efficient use of humic acid fertilizer on the chrysanthemum production, we explored the relationship between the effects of FHA on the growth and development with the photosynthesis and chloroplast ultrastructure in the leaves of chrysanthemum, and the relationship between the effects of FHA on the vase life with the activities of antioxidant enzymes, and the malondialdehyde(MDA) content in cut chrysanthemum flowers.The main results of this study are as follows:1. Effects of humic acid on growth, photosynthesis and chloroplast ultrastructure in chrysanthemum The results show that the stem diameter, fresh and dry weights of shoots and roots, the root to shoot ratios, leaf area in FHA treatment were obviously higher than the control and NPK fertilizer treatments. The results from photosynthesis and chloroplast ultrastructure show that the net photosynthesis rate(Pn) was increased with the increasing time of treatment in three treatments. However, the Pn was significantly higher in the leaves of chrysanthemum sprayed with FHA fertilizer than that of the control and the NPK fertilizer at 60 DAS(days after treatment). With the time of treatment increasing, the Fo and NPQ was gradually lower in FHA treatment than those of the control and the NPK treatment. The Fv/Fm in FHA treatment keeps higher than that of the control and the NPK treatment at all days. The ΦPSII was significantly higher in FHA treatment than that of the control and the NPK treatment after 45 DAS. The content of chlorophyll and soluble sugars, soluble protein in the leaves of chrysanthemumtreated with FHA fertilizer was significantly higher than that of the control and the NPK fertilizer. The grana lamellae stacked closer in NPK treatment and FHA treatment compared with those of the control. However, more organized thylakoids were observed in the leaves sprayed with FHA fertilizer respect with the NPK fertilizer. No obvious change was observed in the shape of the chloroplast ultrastructure.2. Effects of humic acid on leaf transpiration and stomatal characteristic in chrysanthemum The leaf transpiration rate and stomatal conductance in the leaves sprayed with FHA fertilizer were higher than the control and NPK fertilizer treatments. The results from the observation of the leaf stomatal characteristic show that the stomatal density and stomatal opening degree increased by being sprayed with FHA fertilizer compared with the control and NPK fertilizer. The results indicated that FHA fertilizer can improve the stomatal density and stomatal opening degree to improve the leaf transpiration rate, and promote the water and inorganic salt absorbed by roots transport quikly to the overground parts.3. Effects of humic acid on the postharvest vase life and physical signs in cut chrysanthemum flowers The vase life, flower size and fresh weight were obviously higher in FHA treatment than those of the control and NPK treatments. During the vase time, the activities of antioxidant enzymes(SOD, POD, CAT) in cut chrysanthemum flowers were higher than those of the control and NPK treatment, and the malondialdehyde(MDA) content was lower than the other treatments, and significant difference was observed. The results indicated that the foliar humic acid improved the activities of antioxidant enzymes and delayed flower senescence, extended the vase life and ornamental quality of cut chrysanthemum flowers.