Extended Abstract
 
Nowadays, salinity stress is the most important abiotic stress for plants. Using saline water not only decreases yield but also reduces the amount of available fresh water and arable land that can be used for agriculture. By contrast, in soilless or hydroponic cultivation systems, plants are cultivated in an environment other than soil, in order to get to maximum plant density, improve yield and reduce soil contamination and nutrient uptake problems. Considering that tomato is a plant with high nutritional value and that it can be grown in different substrates, choosing a suitable substrate for cultivation with the ability to reduce the effects of salinity is important. In the current study, the effects of using activated carbon and potassium-enriched nanozeolite as an adsorbent were examined. The experiments were conducted under salty conditions (three levels) and the measured factors were: the yield, growth, physiological properties and water use efficiency of tomato.
This experiment was performed as a factorial experiment in a completely randomized design with three replications in the Faculty of Agriculture and Natural Resources of the Persian Gulf, 2022. The experiments were conducted in greenhouse conditions with temperature of 22 ± 5°^C and a relative humidity of 50 to 70%. Cultivation bed and irrigation water salinity were two factors considered in this study. Five types of culture media were prepared including basic culture media (cocopeat and perlite at 2/1v/v) and the treatments of activated carbon and nanozeolite enriched with potassium, at two levels (15 and 30g of each adsorbent were added to the one kilogram of basic culture medium). Saline water was used at three levels of 1.8, 3.5 and 5.5 dS/m of Hoagland solution. Salinity treatments were applied two weeks after the establishment of Adamino tomato seedlings in the culture bed, through the drip solution system, and continued until one week before the end of the experiment (120 days). The measured traits were total yield, average fruit weight, chlorophyll a, b and total, carotenoids, lycopene, vitamin C, TSS, TA of fruit extract, electrolyte leakage, relative content of leaf water, proline and water use efficiency.
The results showed that with increasing salinity to 5.5 dS/m, tomato yield, fruit weight, relative leaf water content, chlorophyll a, b, and total chlorophyll, carotenoid content, and water use efficiency significantly decreased (p< 0.01). However, the application of absorbent had a better effect on these traits by mitigating the impact of salinity. In contrast, increasing salinity elevated the levels of vitamin C, TSS, TA of fruit extract, electrolyte leakage, lycopene and proline of tomato shoots. Adverse effects of salinity on plant growth included osmotic stress, specific ion effects, and nutritional imbalance leading to morphological, physiological and biochemical disturbances. The result indicated that amending the substrate with activated carbon and potassium-enriched nanozeolite increased all studied traits of tomato except vitamin C, at all salinity levels (p< 0.01). The highest yield of tomato (6.66 kg), fruit weight (96.33 g) and water use efficiency (27.75 kg/m³) were related to the treatment of 15 g/kg potassium-enriched in culture medium with the solution of 1.8 dS/m. The application of 15 g/kg activated carbon and 30 g/kg potassium-enriched nanozeolite of culture medium increased the yield and fruit weight by 45% and 28%, respectively compared to the control treatment at the same salinity level. Zeolites consist of large open internal pores with a high cation-exchange capacity in crystal structure that result in high water holding capacity and nutrient retention. That improvement of the plant growth in zeolite-rich treatments may be associated with enhancement of macronutrient supplement and reduction of sodium uptake by plant root. Beside the effect of potassium in nanozeolite, the antagonistic relationship between potassium and sodium resulted in a reduction of sodium absorption by the plant. Therefore, it moderated the negative effects of salinity stress and increased indicators related to growth and yield and water use efficiency of tomato. It seems that the use of activated carbon in this research could reduce the effects of salinity stress due to its high specific surface area and porous structure. In general, the results of this study revealed the beneficial effects of activated carbon and enriched nanozeolite on properties of tomatoes (yield and phytochemical traits), and water use efficiency of tomato under salinity stress conditions.