Ecological implications of the use of Azospirillum brasilense on the microbiome of the soil and rhizosphere of maize

Author(s)

Alexandre Pedrinho

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2024-03-01

Examining board members

Fernando Dini Andreote; Lucas William Mendes; Arthur Prudêncio de Araujo Pereira

• Advisor: Fernando Dini Andreote

Abstract

Azospirillum brasilense is a plant growth-promoting bacterium (PGPB) used as a bioinoculant in agriculture. A. brasilense can establish beneficial associations with plant roots, modifying root metabolism and morphology, improving water and nutrient uptake, and consequently, increasing plant growth and productivity. However, the ability of A. brasilense to establish itself in the bulk soil and rhizosphere of different plants (including maize), as well as its interactions with the native soil bacterial community, is not fully understood. This knowledge gap can be attributed to inconsistencies in the quantity of the inoculant delivered (population size) and different abiotic (e.g., soil pH and nutrient content) and biotic (e.g., competition, predation, and antagonism) factors that modulate its performance. In this study, our objective was to gain a better understanding of how different-sized populations (sub-dose, recommended dose and super-dose) of A. brasilense affect and interact with the structure, diversity, and composition of the native bacterial community in both bulk soil and rhizosphere of maize plants at different growth stages (15 and 30 days after inoculation DAI). Furthermore, we aimed to assess the effectiveness of these populations of these different-sized populations of A. brasilense in promoting the growth of maize plants. Our results demonstrate that the introduction of a large population (recommended dose and super-dose) of A. brasilense significantly improved maize growth parameters (shoot, root and total dry mass), while a small population (sub-dose) did not. In the bulk soil, we observed that large populations (recommended dose and super-dose) of A. brasilense were capable of initially disrupt the native bacterial community in the soil. However, the A. brasilense population rapidly declined, allowing the native bacterial community to recover and return to its initial state. In the rhizosphere of maize plants, large populations of A. brasilense exerted a delayed impact on the native bacterial community, possibly due to permanent changes in plant characteristics such as morphology and root exudation. Furthermore, co-occurrence network analysis (interaction between microorganisms) revealed changes in keystone taxa in the rhizosphere of maize plants. A. brasilense played a fundamental role in the early stages (up to 15 DAI), but was later replaced by Rhizobiales, a native soil bacterium. This study presents novel evidence of how populations of different sizes of A. brasilense can influence microbe-microbe and plant-microbe interactions, affecting the native soil bacterial community as well as the growth of maize plants. (AU)

• FAPESP's process: 19/16006-4 - Ecological implications of the use of microbial inoculants in agricultural soils
• Grantee: Alexandre Pedrinho
• Support Opportunities: Scholarships in Brazil - Doctorate