Response of pot marigold (Calendula officinalis L.) to interaction effects of salt stress and organic soil amendments

Salinity is a major factor reducing plant growth and productivity worldwide; it affects about 7% of the world’s total land area and is the major environmental factor limiting plant growth and productivity. Saline soil can be defined as soil having an electrical conductivity of the saturated paste extract (ECe) of 4 dSm−1 (4 dSm−1 ∼40mM NaCl) or more. The detrimental effects of high salinity on plants can be observed at the whole-plant level such as the death of plants or necrosis of plant organs and/or decreases in productivity. Many plants develop mechanisms either to exclude salt from their cells or to tolerate its presence within cells. During the onset and development of salt stress within a plant, all the major processes such as photosynthesis, protein synthesis, and energy and lipid metabolism are affected.
Calendula officinalis L. belongs to the Asteraceae (Compositae) family; it is an annual with bright or yellow orange daisy-like flowers which are used for medicinal or culinary purposes.
Organic fertilizers develops favorable physical, chemical and biological environments in the soil. They stimulates plant root growth, increase nutrient uptake, decreases evaporation from the soil, increases soil water-holding capacity, reduces surface water runoff, facilitates drainage, regulates soil temperature and provides a rich substrate for soil microbes. This study was conducted to determine the effects of soil salinity and organic amendments on some growth characteristics, concentration of nitrogen, phosphorus and potassium and catalase enzyme activity in pot marigold plant (Calendula officinalis L). In a factorial experiment and completely randomized design (CRD), five levels of organic amendments (control, 0.5 and 1 g.L-1 algae extract, 20% v/v cow manure and 20v/v of pot volume vermicompost) and three levels of salinity (3.5, 7.5 and 10.5 dS.m-1) with three replications per treatments were applied. In this experiment, media without organic amendment was considered as control. Results showed that increasing soil salinity levels progressively decreased the growth characteristics and nutrient concentration. Salinity causes growth reduction due to the low osmotic potential of the medium and by a specific ion effect as a secondary cause in several vegetable crops. The results of present study showed that the organic media can improve plant height. This can be due to increased media moisture storage and enhanced nutrient absorption. The maximum leaf area, plant height, fresh and dry weight of shoots and roots and nitrogen, phosphorus and potassium concentrations obtained in cow manure treatment and EC= 3.5 dS/m. While, the highest chlorophyll content and the lowest RWC was observed in cow manure treated plants in media with EC= 7.5 dS/m. In pot marigold, an increase in salinity significantly decreased shoot and root fresh and dry weight. Excess soluble salts in the root zone restrict plant roots from withdrawing water from surrounding soil, effectively reducing the plant available water, i.e. causes drought for the plant. The loss of photosynthesis in salt stress conditions resulted in the loss of dry weight production at the leaf level of pot marigold. Cow manure significantly increased leaf area in pot marigold as compared to the control.
All treatment significantly increased growth characteristics of pot marigold compare to control. The positive effect of cow manure to nutrients absorption could be because of it was rich of N, P, K compare to the others. Plant height, chlorophyll, RWC and potassium concentration of leaves showed positive correlation to other characteristics. The catalase enzyme was also showed positive correlation to other traits except fresh and dry weight of root and N and K concentration. According to the results, it is cleared that in normal condition, pot marigold plant could tolerate salt stress until 7.5 dS/m but by suitable media culture its threshold tolerate will be increased until 10.5 ds/m. Also it was revealed that cow manure compare to other treatments could increase plant tolerate to salt stress and growth characteristics.