Elemental composition of strawberry plants inoculated with the plant growth-promoting bacterium Azospirillum brasilense REC3 assessed by scanning electron microscopy and energy dispersive X-ray analysis

Abstract

The elemental composition of strawberry plants (Fragaria ananassa cv. Macarena) inoculated with the plant growth-promoting bacterium Azospirillum brasilense REC3 and non-inoculated controls, was studied for the first time by using scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analysis. This technique allowed semi-quantification of different elements simultaneously using a small solid sample. Plants were inoculated and grown hydroponically in 50 % and 100 % Hoagland solution, corresponding to a poor- or rich- nutrient medium, respectively. Bacterial inoculated plants increased 45% and 80 % strawberry growth index compared to their controls when grown in 100% and 50% Hoagland solution, respectively. Thus, inoculation with A. brasilense REC3 in a poor-nutrient medium had the largest effect in terms of increasing both shoot and root biomass as well as growth index. SEM-EDS spectra and maps showed the elemental composition and relative distribution of nutrients in strawberry tissues. Leaves were composed of C, O, N, Na, P, K, Ca and Cu, while roots had also Si and Cl. The organic fraction (C, O and N) accounted for over the 96.3 % of the total chemical composition, and among the mineral fraction composition, Na exhibited a higher accumulation in both tissues. Azospirillum-inoculated and control plants showed similar elemental quantification values. Although, in bacteria-inoculated roots, P was significantly increased (34.33 %) while Cu was decreased (35.16 %).