Fascinating Role of Silicon dioxide Nanoparticles and Co-inoculation of Mycorrhiza and Rhizobacteria to Combat NaCl Stress: Changes in Physiological Characteristics, Uptake of Nutrient Elements, and Enhancing Photosystem II Activities in Wheat

Salinity stress is one of the global problems that limit crop production. The application of silicon dioxide nanoparticles (SiO2-NPs) and the inoculation of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) with wheat are novel approaches to reducing the negative effects of salinity stress. Therefore, the main objective of this experiment was to investigate the role of SiO2-NPs and the use of co-inoculation of AMF and PGPR for wheat plant tolerance under salt stress. The experiment was carried out as a factorial based on a randomized complete block design. Accordingly, a pot experiment was conducted on wheat growing under salt stress (0, 35, 70, and 105 mM NaCl), using bio-fertilizers (control, mycorrhizal fungi, Flavobacterium and Pseudomonas bacteria, co-inoculation of AMF and PGPR), and SiO2-NPs (0, 30, and 60 mg/L) as additives. The results showed that, under 105 mM salinity stress, the co-inoculation of AMF and PGPR as well as the use of SiO2-NPs enhanced chlorophyll a (8.81%), b (12.93%), total Chl (22.68%), carotenoid content (18.88%), membrane stability index (14.82%), plant height (13.37%), and spike length (13.9%) parameters compared to control treatment. The application of AMF and PGPR individually or in combination and the use of SiO2-NPs improved physiological parameters such as leaf area index, chlorophyll fluorescence parameters, anthocyanin, and chlorophyll index. Salinity stress reduced the uptake of phosphorus and K+, as well as increasing the uptake of Na+. However, co-inoculation of AMF and PGPR as well as 60 mg/L SiO2-NPs resulted in increased Si, P, and K+, as well as decreased Na+ uptake, which finally increased grain yield. Generally, this finding implies that co-inoculation of AMF and PGPR as well as the application of SiO2-NPs could be used as additives for the improvement of wheat and the uptake of nutrients under salinity stress.