Bacillus subtilis QST713 and cellulose amendment enhance phosphorus uptake while improving zinc biofortification in wheat

Abstract Phosphorus (P) in an essential non-renewable resource in agriculture and zinc (Zn) deficiency is an important micronutrient imbalance in calcareous soils. Inoculation with Bacillus subtilis QST713 and amendments with readily available C for soil microorganisms is known to enhance the uptake of some nutrients by plants. We hypothesized that these practices may also improve P and Zn uptake. However, since Zn and P are antagonistic nutrients, it is also relevant to assess if a potential enhancement of P nutrition worsens Zn uptake by plants. An experiment with wheat ( Triticum durum L) was performed involving three factors: (i) treatments affecting rhizospheric microorganisms: control without treatment, cellulose as readily C source for microorganisms, and inoculation with B . subtilis QST713, (ii) soil type: Vertisol and Alfisol, and (iii) P source: unfertilized control, and rock phosphate. The supply of cellulose improved total P uptake by plants in both soils independently of the P supply. Overall, inoculation with B . subtilis also provided benefits on P uptake, despite this effect varied depending on soils and P supply. B . subtilis improved Zn concentration in grains by 24% relative to untreated control, while the effect on total Zn uptake by plants was non-significant. This explained the increased Zn harvest index with B . subtilis . The improvement of P uptake by B . subtilis and cellulose did not lead to an antagonistic effect on Zn, whose uptake by plants increased linearly with increased P uptake (R 2  = 0.68; P B . subtilis increased Zn accumulation in edible parts, thus promoting a biofortification effect.