Mitigação de estresse por encharcamento em soja promovida por Azospirillum brasilense e extrato de algas

Abstract

Soybean is a crucial crop in Brazilian agriculture, but its development can be compromised by waterlogged soil. Alternatives to mitigate these effects include the use of biostimulants, such as Ascophyllum nodosum seaweed extract, and the inoculation of plant growth-promoting bacteria, such as Azospirillum brasilense. The objective of this study was to evaluate the development of soybean crops in waterlogged soil inoculated with A. brasilense or foliar application of A. nodosum extract, and to study their benefits on photosynthetic, anatomical, biometric, and productive variables. The trial was conducted in a randomized complete block design with four replicates in triplicate. The treatments were: T1 - plants grown in soil near field capacity (control); T2 - plants inoculated via seed with A. brasilense and in soil near field capacity; T3 - plants subjected to foliar spray of seaweed extract (A. nodosum) and in soil near field capacity; and T4 - plants inoculated via seed with A. brasilense + foliar spray of seaweed extract (A. nodosum) and in soil near field capacity; T5 - plants exposed to waterlogged soil (waterlogged control); T6 - plants inoculated via seed with A. brasilense and exposed to waterlogged soil; T7 - plants subjected to foliar spray of seaweed extract (A. nodosum) and exposed to waterlogged soil; and T8 - plants inoculated via seed with A. brasilense + foliar spray of seaweed extract (A. nodosum) and exposed to waterlogged soil at the beginning of pod development (R3). The experimental plot consisted of 12-liter pots with two plants per replicate. Foliar application of seaweed extract occurred at phenological stages V5 and R1. Ten and 20 days after imposition of waterlogging, samples were collected for anatomical, biometric, and physiological evaluations of gas exchange. Production evaluations were performed at the end of the cycle. Soil waterlogging impaired photosynthetic activity, photosynthetic pigments, SPAD index, and foliar nitrogen and phosphorus contents. Although bioinputs did not directly contribute to the maintenance of these factors, they contributed positively to other variables, reducing the impacts of stress on production. Foliar application of seaweed extract (A. nodosum) was more effective in preserving biometric and productive characteristics, minimizing losses. On the other hand, inoculation with A. brasilense showed less significant responses in mitigating the negative effects. Anatomical analysis revealed root acclimation to waterlogging. Inoculation with A. brasilense increased root diameter and the number of metaxylems, suggesting stimulation of root development. Foliar application of seaweed extract, alone or combined with A. brasilense, promoted an increase in the diameter of the central cylinder and the number of metaxylems, indicating an improvement in the conduction of water and nutrients.