Contribuição de Bacillus aryabhattai e silício em Mimosa caesalpiniifolia sob estresse hídrico: respostas morfofisiológicas e atividade biológica do solo

Abstract

Mimosa caesalpiniifolia Benth. (commonly known as sabiá) is a native leguminous tree used in agroforestry systems, the recovery of degraded areas, and wood production. Despite its rustic nature, its seedlings are sensitive to water deficit during the initial growth stage, which compromises performance, especially in semiarid regions. Sustainable strategies, such as the use of plant growth-promoting microorganisms and beneficial elements like silicon (Si), have been studied to enhance drought tolerance. Bacillus aryabhattai stands out for its ability to solubilize phosphorus, produce phytohormones, and stimulate microbial activity. Silicon, in turn, helps mitigate abiotic stresses by strengthening plant structures and activating antioxidant mechanisms. This study evaluated the effects of inoculation with B. aryabhattai and silicon application on growth, plant physiology, and soil microbial activity in sabiá seedlings under water stress conditions, using different irrigation levels (50% and 100% of field capacity). The experiment was conducted in a greenhouse using a completely randomized factorial design (2×4), considering: (i) treatments (control, B. aryabhattai, silicon, and B. aryabhattai + silicon) and (ii) irrigation levels (50% and 100%), with four replicates. Morphological variables, quality indices, photosynthetic pigments, water use efficiency, and microbiological and enzymatic indicators of the soil were evaluated. Full irrigation resulted in the greatest morphological and seedling quality gains. However, even under stress, the combination of silicon and B. aryabhattai promoted gains in plant height, stem diameter, robustness index, and leaf pigmentation. Water use efficiency was higher under stress conditions, suggesting physiological adaptation. Microbial and enzymatic soil activity was mainly stimulated by B. aryabhattai, with notable increases in basal respiration, microbial biomass carbon, and the metabolic quotient. Silicon accumulation occurred predominantly in the roots, being higher in treatments where the element was applied. It is concluded that the combination of B. aryabhattai and silicon is a promising strategy for producing seedlings more tolerant to drought.