Influence of three types of superabsorbents on growth characteristic and elements uptake in basil under salinity stress

Introduction: Salinity stress is one of the main factors that limited crop production.Based on the severity and duration of the salinity stress, the plants show different reactions. First of all, salinity reduces the growth of plants due to the existing osmotic materials around the roots. Furthermore, salinity exerts hypertonic stress on the plants. Under salt stress, ions, mostly Na+ and Cl-, accumulate in the tissues of plants and cause significant physiological and biochemical disorders, reactive oxygen species (ROS) production, and inhibition of K+ uptake. Therefore, these occurrences lead to a reduction in plant growth and development. So using different methods for reducing the harmful effects of salinity is very important. Superabsorbent polymers application has extended to aid the growth of plants in saline soils. These substances have been applied as a soil amendment to improve plant growth under salt stress. Basil is a medicinal plant from the Lamiaceae family that used in the food and cosmetic industries.
Materials and Methods: To study the comparison between three types of superabsorbent on growth characteristics and basil elements content under salinity stress in two harvesting times, a pot experiment was conducted at the research greenhouse of Ferdowsi University of Mashhad as factorial based on the completely randomized design with four levels of NaCl (0, 40, 80 and 120 mM NaCl in irrigation water (Respectively: 0, 3.5, 7 and 10.5 dS/m) and four levels of super absorbent polymers (control, Ackoasorb, Stockosorb and Terracottem) in three replications in 2019. The studied traits were included growth characteristic (Plant height, Number of brunches, Stem diameter, Internode distance, Length and width of Leaf, Spike height, Fresh and dry weight of Leaf, Stem, and Spike) and element content (N, P, K, Na, K/Na, Ca and Mg). Statistical analysis was performed using Minitab 17 software. The mean comparison was done by the Bonferroni test at the 5% probability level. The figure drew by Microsoft Excel software.
Results and Discussion: The results of the mean comparison in both harvesting times showed that, with increasing salinity, the growth characteristics of the plant decreased and the application of superabsorbents, especially in the second harvesting time, improved these traits. In the first harvesting time, the amount of potassium, phosphorus, and nitrogen was increased by using Terracottem superabsorbent polymer 28.43, 68.96, and 71.55, respectively. Moreover, potassium to sodium ratio was increased by applying Ackoasorb superabsorbent polymer 18.85%, in 120 mM salinity compared to the control. Also, the results showed that at the highest salinity level, the application of all three types of superabsorbent polymers was able to significantly decrease sodium compared to the control. On the second harvesting time, the results showed that at the highest salinity level (80 mM), potassium and phosphorus levels increased by 34.66% and 44.44%, respectively, and the sodium content was 19.95% higher than the control. It seems that superabsorbents with water storage and reduction of salt concentration around the root can reduce the negative effects of NaCl stress. Among the superabsorbents used in this study, the Terracottem was more effective.
Conclusions: Based on the results of this experiment, the growth characteristics and elements of O. basilicum cv. Keshkeni luvelu were influenced by NaCl. At the higher NaCl levels, the negative effects of NaCl on plants and osmotic abilities were observed. The application of superabsorbent polymers had different effects on the studied traits. In most cases, Terracottem was the most effective superabsorbent to mitigate the negative effects of salinity. Superabsorbent polymers application can protect the plants from harmful effects of salinity by increasing K+ amount as well as decreasing Na+. However, there is little knowledge about the mechanism of superabsorbent polymers' application under salinity stress in the previous study. The findings of this study indicated that superabsorbent polymers application, especially the Terracottem can alleviate the negative effects of salinity on sweet basil by increasing water holding capacity and decreasing Na+ concentration.