Investigating the EFfect of Coated Nanoparticles )Silicon oxide) on Increasing Salinity Tolerance of Black Cumin (Nigella sativa L.)

Introduction
Abiotic stresses pose serious risks for growth and production of crop in the world. Salinity is among the most important environmental stresses that makes limitations to agricultural production in arid and semi-arid regions. Twenty seven million hectares was affected from salinity in Iran. Salinity stress disrupts some plant processes by reducing the osmotic potential, and disrupting the absorption and transfer of certain essential nutrients such as calcium (Ca) and potassium(K). Moreover, direct toxic effects of ions such as sodium (Na) and chlorine (Cl) on cell membranes, as well as enzymes of the plant, disrupt some plant processes. Furthermore, the secondary aspect of all environmental stresses is production of reactive oxygen species (ROS) that makes oxidative damages. Effective strategies to reduce negative effects of salinity stress include the separate or combined use of saline soil amendment methods, cultivation of compatible plants with saline conditions such as medicinal plants, application of optimal levels of chemical fertilizers such as silicon (Si), use of plant growth regulating agents such as humic acid (HA) and salicylic acid (SA), use of nano-fertilizers to improve the nutrient utilization efficiency, and growth stimulants applying.  Therfore current research was performed to investigate the effects of SiO_2-nanoparticles coated with humic acid (coHA-nSi) on yield, ion composition and salt tolerance of black cumin (Nigella sativa L.) under laboratory and greenhouse conditions in 2016-2017.
 
Material and Methods
The laboratory experiment was conducted to obtain the adsorption rate and maximum adsorption of HA on the nSi. Total carbon in coHS-nSi as an indicator of HA was determined by using Carbon Analyze requipment (Vario El, Elementar, Germany).The size of nSi was measured by Transmission Electron Microscopy (TEM-EM10C-100KV-Zeiss-Germany) before and after coating process . The greenhouse experiment was conducted to apperceive the effectiveness of coHS-nSi on the yield, ion composition, and the increase of salt tolerance of black cumin(Nigella sativa L.). The treatments were arranged in a split plot design based on Randomized Complete Block Design(RCBD) with four replications and two observations in each plot. The main factor was salinity (NaCl in irrigation water)at three levels including 2 as the control, 3.5 and 5 dS/m, which applied 20 days after transplanting. The subplot was concentration of coHS-nSi in irrigation water at four levels including 0, 0.25, 0.5 and 0.75 g/l,that applied at two growth stages including15 days (p1) and50 days (flowering stage) (p2) after planting. Plants were harvested at maturity stage of seeds. Seed yield and biomass dry weight, harvest index, 1000-seed weight, the number of mature capsules, and the number of seeds were calculated per square meter (number of plants/m2=50). RWC [21] and ion leakage (IL)[22] of black cumin were evaluated as physiological parameters (ten weeks after transplanting). All data was subjected to analysis of variance (ANOVA) by using MSTAT.C software. Duncan's new multiple range test (DNMRT) at 5% probability level was used for mean comparison. Also, the graphs were drawn by Excel.
 
Results and Discussion
The laboratory results showed that the carbon adsorption as an indicator of HA on nSi was increased from 7.6 to 111.9 mgC/g and reached to maximum at 1.6 g/l of HA. Also, the adsorption rate of HA on nSi illustrated that it increased exponentially and peaked at 120 hours. The diameter of nSi was about 20-30 nm and did not change significantly during the experiment. It was confirmed by micrograph made with Transmission Electron Microscopy (TEM-EM10C-100KV-Zeiss-Germany). The greenhouse results demonstrated that the seed yield and biomass dry weight harvest index, and number of capsules and seeds were affected by salinity significantly. These parameters were reduced at 5 dS/m. Furthermore, the application of 0.5 g/l coHA-nSi increased significantly the seed yield and biomass dry weight, harvest index, and number of capsules at all salinity levels.. The biomass dry weight and seed yield was increased by 20 and 30% at 0.5 g/l coHS-nSi treatment, respectively. The results illustrated that these parameters reached to maximum by application of 0.5 g/l coHS-nSi at 5 dS/m. The results of nutrient uptake by black cumin illustrated that the salinity affected the uptake of N, K, Ca, Mg, Fe and ratio of K/Na and Ca/Na while it was not affected S uptake. The application of coHS-nSi affected the uptake of N, K, Mg, Na, S and K/Na ratio at leaves, significantly. The uptake of N, K, Mg, Na, S and K/Na ratio increased by 20, 20, 10, 20, 26 and 16%, respectively at the 0.5 g/l compared to the control. The percentage of IL and RWC of black cumin leaves was influenced by salinity and coHS-nSi treatments. The lowest IL and the highest RWC of leaves were found at 0.5 g/l coHS-nSi treatment at all salinity levels.
 
Conclusions:
The covering of nSi with HA in the presence of SA (coHS-nSi) investigated in laboratory conditions based on the carbon adsorption on nSi. The adsorption rate increased with increment of HA concentration and contact time. The outcome indicated that the maximum adsorption of carbon with nSi was 111.9 mgC/g. The diameter of nSi did not change significantly during the experiment according to micrograph made with Transmission Electron Microscopy. The results illustrated that application of 0.5 g / L coHS-nSi significantly increased biomass dry weight, grain yield, harvest index and the number of mature capsule in black cumin at salinity of 5 dS/m. Moreover, the application of coated nanoparticles not only increases the strength of cell wall but also increased uptake of nitrogen, potassium and magnesium. Therefore, it is concluded that coating of nSi with HA in the presence of SA(coHS-nSi), make a reduction to the amount and frequency of its usage and increase the salinity tolerance by improving the quantity and quality of black cumin.