Effect of Different Iron Concentrations and StaircaseIron Regime on Some Morphological, Biochemical and Flowering Characteristics of Calendula officinalis

While Iron (Fe) is the fourth most abundant element in the earth’s crust, it is not easily available for plant roots. Therefore, Fe deficiency is one of the major limiting factors for plant growth and development in calcareous soils worldwide. Fe deficiency are also predominant in many areas of Iran. It is an essential micronutrient for plants that play vital roles in many metabolic processes. Fe is a component of a number of molecules such as Fe-sulfur (Fe-S) and heme Fe proteins, which are required for photosynthesis, respiration and N2 fixation. However, the possibility of using split-type fertilization at different growth stages during development has been explored in other plant species for macronutrients N, P, and K. The aim of this work was to test the hypothesis that it may be feasible to decrease Fe-chelate inputs, by studying the effect of gradually increasing of Fe concentration during Calendula officinalis growing period.

In order to study the effect of gradual increase of Fe concentration during Calendula officinalis growing period, an experiment was carried out as a completely randomized design with four replications (pots) at research greenhouse of Faculty of Agriculture, Lorestan University, in 2017. Treatments contained three levels of Fe (Fe-chelate Fe (III)- Ethylenediamine-N, N' –bis ((2-hydroxyphenyl) acetic acid): 4, 20 µM and staircase method. Staircasetreatment included increase of Fe concentration, so that at first week plants received 4 µM Fe then 2 µM was added to Fe concentration weekly, to reach 26 µM. Some morphological, physiological parameters, flower characteristics and gas exchange had measured. Data of all measured parameters were subjected to analysis of variance using the SAS software (9.1.3, SAS Institute Inc.), and means were compared using a Duncan test at P≤ 0.05.

Results showed that the application of 4 µM Fe led to higher root volume, and peroxidase activity. Romera et al. (2011) reported that under Fe deficiency, strategy of plants developed morphological changes in their roots and up-regulated the expression of Fe acquisition genes. Under Fe deficiency some phytohormones such as ethylene and auxin will increased. Both hormones play pivotal role in the development of sub-apical root hair and transfer cells. Sepahvand et al (2017) investigated the effect of ascorbic acid on pelagonium graveolens characteristics under Fe deficiency and found that peroxidase activity increased under Fe deficiency. Application of ascorbic acid led to decrease peroxidase activity. Maximum biomass was obtained in plants under 35 µM Fe and staircase treatment. Maximum chl a and b, chl a+b, carotenoids, root dry weight, flower diameter, flower longevity, number of flowers, and first flower fresh weight was observed in the plants under staircase treatment. Fe plays important role in biosynthetic pathway of chlorophyll and carotenoids. In addition, plants under staircase treatment showed the maximum photosynthesis and transpiration rate. Kong et al. (2014), reported that Fe deficiency led to decrease of δ- aminolevulinic acid and protochlorophyllide as precursors of chlorophyll. Ethylene and ABA are involved in Fe-deficiency signalling in plants, and these compounds may hasten senescence (Satoh, 2011). The short flower lifetime found in the present experiment in the low Fe treatment may be due to the boost in ethylene and ABA synthesis in response to Fe deficiency. On the other hand, plants under staircase regime had higher photosynthetic pigments that led to maximum photosynthesis. Increasing flower quality, quantity and longevity related to higher photosynthesis activity. Iron is a component of a number of proteins and enzymes, such as iron-sulfur (Fe-S) proteins and non-heme iron proteins, which are required during photosynthesis (Chakraborty et al., 2012). Li et al. (2016) investigated the influence and interaction of Cadmium (Cd) and Fe on photosynthesis and reported that Cd inhibits photosynthesis activity, but Fe alleviates the Cd-induced changes in photosynthesis activity. In addition, higher MDA contents were observed in plants under 35 µM Fe and staircase treatment. Li et al. (2012) reported that the high levels of Fe led to maximum MDA contents.

Growing the plants with staircase treatment increased flower yield, quality and longevity. These parameters are the most important factors in growing of ornamentals plants. Whereas Fe fertilizers are so expensive, restricting the use of expensive products such as Fe (III)-chelates at some growth stages can contribute to decrease the cultivation costs and minimize environmental pollution associated to an excess of fertilizer inputs. Therefore, gradually increasing Fe concentrations during production of Calendula officinalis under soilless culture would be recommended.