Phosphorus bioavailability and silicon fractionation in wheat rhizosphere affected by soil water content and silicon application

Abstract

Drought stress limits plant growth by reducing water and nutrient uptake. This study examined the effects of silicon (Si) and soil water content (SWC) on Si fractionation and phosphorus (P) bioavailability in the wheat rhizosphere, as well as their uptake under drought stress. The experimental setup involved dividing pot soil into rhizospheric and non-rhizospheric (bulk) zones using rhizobags. Wheat seeds were grown under different Si treatments (0, 150, 300 mg/kg monosilicic acid, and 150, 300 mg/kg Si nanoparticles) and SWC (0.4 and 0.8 Field Capacity). Results demonstrated that plant-available Si and adsorbed Si concentrations in the rhizosphere were 16.3% and 10.8% higher than in bulk soil, respectively, while amorphous Si was 17.4% higher in bulk soil. Drought stress decreased plant-available Si and adsorbed Si in the rhizosphere by 14.9% and 10.8%, respectively, while increased amorphous Si by 8.2%. Si application enhanced plant-available Si, adsorbed Si, and amorphous Si in both rhizosphere and bulk soil. Phosphorus bioavailability in the rhizosphere was 1.44 times higher than in bulk soil, and drought stress reduced plant-available P by 9.1% and 6% in the rhizosphere and bulk, respectively. Si treatments increased P bioavailability in the rhizosphere by 10.3–21.2%. Reduced rhizosphere pH (up to 0.5–1 unit) and increased organic carbon (up to 19–48%) mediated by Si contributed to higher P availability. Drought stress decreased leaf P content by 15–48%, while Si treatments increased it by 55.4–148.5%. Si-mediated improvements in P uptake were linked to enhanced water uptake, as indicated by a 23.1–37.3% increase in leaf water content and an 11.4–36.4% increase in transpiration rate under drought stress. These findings highlight Si's role in improving wheat drought tolerance by modifying rhizosphere properties and facilitating water and nutrient uptake. Therefore Si application can be considered in fertilization programs in arid and semi-arid regions.