Ascophyllum nodosum, Bacillus subtilis e silício mitigam efeitos do déficit hídrico no crescimento e na fotossíntese em mudas de Myracrodruon urundeuva?

Abstract

Myracrodruon urundeuva, popularly known as aroeira-do-sertão, is a native tree species naturally distributed across several states of Brazil. Climatic factors change suddenly, causing severe water deficit conditions and negatively impacting photosynthesis and seedling growth. New technologies and sustainable innovations have been proposed to mitigate water deficit stress, including Bacillus subtilis, a plant growth-promoting bacterium, Ascophyllum nodosum L., a brown seaweed, and silicon, a beneficial mineral, all of which have increasingly demonstrated promising potential for agriculture by contributing to plant resilience and the biostimulation of physiological and biochemical processes. The objective of this study was to evaluate the effects of these mitigating agents on the photosynthesis and growth of Myracrodruon urundeuva seedlings. The experimental design was a randomized block design arranged in an 11 × 2 factorial scheme, with eight replications and two plants per pot. The factors under study consisted of one dose of silicon (Si) (0.84 g L⁻¹), two doses of seaweed extract (A. nodosum) (A15 = 15 mL L⁻¹ and A30 = 30 mL L⁻¹), and bacterial inoculation with B. subtilis (B5 = 5 mL L⁻¹ and B10 = 10 mL L⁻¹), in addition to the presence or absence of silicon associated with the extracts, applied via foliar spraying. The following treatments were evaluated: 1) control (CK) (70% water retention capacity – WRC); 2) water deficit (WD) (40% WRC); and water deficit associated with the following treatments: 3) 0.84 g L⁻¹ Si; 4) A15; 5) A30; 6) B5; 7) B10; 8) A15 + Si; 9) A30 + Si; 10) B5 + Si; and 11) B10 + Si. The results demonstrated that water deficit stress negatively affected the plants, reducing the photosynthetic rate and suggesting physiological sensitivity, although it did not negatively impact biomass accumulation. The application of A. nodosum, especially at the dose of 30 mL L⁻¹, proved to be effective, promoting increases in leaf area, stem diameter, and photosynthetic rate. Silicon promoted adjustments mainly in leaf area and, when combined with A. nodosum, showed the ability to reverse stress effects. On the other hand, the effects of B. subtilis varied among the evaluated doses. This study provided knowledge and technology for forest-based agriculture, promoting adaptation to adverse conditions and benefiting productivity and sustainable bioeconomy.