Effects of Chemical Fertilization and Microbial Inoculum on Bacillus subtilis Colonization in Soybean and Maize Plants

Abstract

Plant growth-promoting endophytic microorganisms in agriculture have been expanding in Brazil and are an excellent strategy to face the challenges of current agriculture, such as reducing production costs with fewer environmental impacts, without detriment to productivity. However, little is known about the factors that can affect the colonization of endophytic such as inoculant concentration and mineral fertilization. The present study aimed to evaluate the influence of these factors on soybean and maize crops and found that for soybean crops, the highest Bacillus subtilis concentration of 1 × 104 and 1 × 1010 CFU ml−1 promoted the highest number of recovered bacteria, when there was no mineral fertilization. However, mineral fertilization limited the number of recovered bacteria, suggesting that mineral fertilization interferes with endophytic colonization. For maize crops, the highest number of recovered bacteria occurred from the concentration of 1 × 106 CFU ml−1, not differing from the highest concentrations. A mineral fertilization dose of 25% promoted the greatest B. subtilis recovery compared to the other treatments. Regarding plant development, the highest microbial inoculum concentrations did not necessarily promote greater positive growth promotion effects compared to the concentration of 1 × 104 CFU ml−1 for both crops. The results also suggest that the higher number of endophytic bacteria recovered in the plant does not necessarily affect plant growth in the same proportion. For soybean plants, there is a strong tendency that with the increase in the B. subtilis inoculant concentration, the need for mineral fertilization doses to achieve the same plant development is consequently increased, and inoculations with 1 × 105 and 1 × 106 CFU ml−1 with fertilization doses between 44% and 62% are the ideal combinations for greater plant development. In maize plants, the best growth promotion response (height) was obtained using inoculation concentration of 1 × 102 and 1 × 1010 CFU ml−1, increasing according to the increase in fertilization doses. The findings suggest, for soybean crop, that these high inoculum concentrations required more photosynthetic metabolites from the plants and more nutrients from the soil. Thus, the need for mineral fertilization for plant growth must be increased.

Potential of Bacillus pumilus to directly promote plant growth

“…Also, it is worth mentioning that the survival rate of bacterial inoculants in the soil largely depends on the indigenous soil microbiota; the survival of PGPB in the soil is high when the diversity of native microbiota is low and vice versa ( Mallon et al, 2015 ; Manfredini et al, 2021 ). In addition, ( Bueno et al, 2022 ) carried out an interesting study on the persistence of B. subtilis in the endosphere of soybean roots, showing that after the application of concentrations of 1 × 10 4 CFU ml −1 and 1 × 10 10 ml −1 , a higher abundance of this strain was recorded a few weeks after inoculation compared to B. subtilis abundance in treatment: B. subtilis + mineral fertilization (the study based on transformed B. subtilis with ampicillin resistance gene).…”

Optimizing tomato seedling growth with indigenous mangrove bacterial inoculants and reduced NPK fertilization

“…This is consistent with several previous studies on other crops worldwide such as wheat ( Triticum turgidum spp. durum L.) in Tunisia ( Tounsi-Hammami et al., 2022 ), maize ( Zea mays L.) in Brazil ( Bueno et al., 2022 ), and cucumber ( Cucumis sativus L.) in Italy ( Scagliola et al., 2021 ).…”

“…Our findings supported those of Yadav et al (2009), who reported that the population of G.diazotrophicus in rhizospheric sugarcane was negatively affected by the addition of synthetic nitrogen. It was reported that high levels of synthetic inputs may enter the bacterial cells and disturb their metabolism, which decreases their abundance in rhizospheric soil (Reid et al, 2021), leading to significant reductions in root colonization (Bueno et al, 2022). It can be suggested that high levels of synthetic fertilizers lead to greater nutrient availability in rhizospheric soils, which may limit the plant's need to interact with beneficial microorganisms in the rhizosphere (Meena et al, 2017).…”

Investigating a microbial approach to water conservation: Effects of Bacillus subtilis and Surfactin on evaporation dynamics in loam and sandy loam soils

“…Developing an improved understanding the soil environments that facilitate B. subtilis colonization and production of Surfactin will be important for further advancement of this approach. For example, the presence of specific genera of bacteria in the soil, such as Lysinibacillus (Kiesewalter et al, 2020), may stimulate Surfactin production from B. subtilis to facilitate wetting, while use of mineral fertilizers can have a negative impact on B. subtilis colonization (Bueno et al, 2022) and therefore would also be expected to impact its wetting potential.…”