Silica nanoparticles boost growth and productivity of cucumber under water deficit and salinity stresses by balancing nutrients uptake

The role of amorphous silica nanoparticles (SiNPs) in enhancing growth and yield of cucumber under water deficit and salinity stresses was assessed. A field experiment under greenhouse conditions was established using 4 different levels of SiNPs (100, 200, 300 and 400 mg kg-1) and 3 different watering regimes calculated based on crop evapotranspiration (ETc) (100, 85 and 70% of ETc). Electrical conductivity and sodium adsorption ratio of irrigation water were 1.7 dS m-1 and 4.63 respectively. The results revealed that SiNPs improved growth and productivity of cucumber regardless of quantity of supplied water; however, the greatest increase corresponded to irrigating cucumber at the rate of 85% of ETc. Applying SiNPs at rate of 200 mg kg-1 showed the greatest increase specially when cucumber plants received 85% of their ETc causing an increase of 20, 51 and 156% in plant height, chlorophyll and fruit yield, respectively, compared to untreated plants. These increases could be due to alerting nutrient uptake as SiNPs clearly increased contents of nitrogen (by 30%), potassium (by 52, 75 and 41% in root, stem and leaf, respectively) and silicon (by 51, 57, 8 and 78% in root, stem, leaf and fruit, respectively). Otherwise, same treatment reduced sodium uptake by 38, 77 and 38% in root, stem and leaf, respectively; consequently, potassium-sodium ratio increased by 149, 735 and 127% in root, stem and leaf, respectively. The significant role of SiNPs in mitigating water deficit and salinity stresses could be referred to high silicon content found in leaf which regulates water losses via transpiration. Also, high K+ content found in roots of cucumber helps plants to tolerate abiotic stresses as a result of maintaining ion homeostasis and regulating the osmotic balance as well as controlling stomatal opening which helps plants to adapt to salinity and water deficit stresses.