Phosphogypsum’s impact on growth and nutrient acquisition in carob trees (Ceratonia siliqua L.) inoculated with native microbiota

Abstract Phosphogypsum (PG) management is one of the major challenges of the phosphate industries in Morocco and worldwide. Its efficient management and valorization at a low-cost and without additional treatment are highly desirable. The purpose of this study is to evaluate the effects of Moroccan PG on the growth and development of carob tree (Ceratonia siliqua) in the presence and absence of its native microbiota. The analysis of the native microbiota revealed that the bacterial community was primarily dominated by Actinobacteria and Proteobacteria, while the fungal community was mainly composed of Ascomycota and Basidiomycota. In the absence of the consortium microbiota, the heights, root dry weights, shoot dry weights and leaflet numbers increased significantly (p < 0.05) in carob plants grown on soil substrates amended with PG at a ratio of 2 % compared to those grown without PG (0 %). Micronutrient (Zn, Fe, Cu, Mn, Ni and Co) contents also increased with PG doses in both the roots and leaves although toxic elements (As, Cd and Pb) were also detected, especially in carob plants grown at 10 and 20 % PG. Inoculation with consortium microbiota in combination with PG had similar beneficial effects on the different physiological parameters measured in the carob plants. The most significant growth was recorded in carob seedlings grown under PG doses of 1 and 2 % and these plants also displayed a better performance against toxic elements. In fact, toxic element concentrations in inoculated carob seedlings grown in PG amended soil were lower compared to non-inoculated plants and far below ranges considered phytotoxic for vascular plants for both inoculum treatments. Our results open up exciting perspectives for the valorization and more widespread use of phosphogypsum in combination with native microorganisms in crop cultivation particularly in regions with difficult soil conditions.