Luis Felipe Guandalin Zagatto

Microbial inoculation stands as a pivotal strategy, fostering symbiotic relationships between beneficial microorganisms and plants, thereby enhancing nutrient uptake, bolstering resilience against environmental stressors, and ultimately promoting healthier and more productive plant growth. However, while the advantageous roles of inoculants are widely acknowledged, the precise and nuanced impacts of inoculation on the intricate interactions of the rhizosphere microbiome remain significantly underexplored. This study explores the impact of bacterial inoculation on soil properties, plant growth, and the rhizosphere microbiome. By employing various bacterial strains and a synthetic community (SynCom) as inoculants in common bean plants, the bacterial and fungal communities in the rhizosphere were assessed through 16 S rRNA and ITS gene sequencing. Concurrently, soil chemical parameters, plant traits, and gene expression were evaluated. The findings revealed that bacterial inoculation generally decreased pH and V%, while increasing H+Al and m% in the rhizosphere. It also decreased gene expression in plants related to detoxification, photosynthesis, and defense mechanisms, while enhancing bacterial diversity in the rhizosphere, potentially benefiting plant health. Specific bacterial strains showed varied impacts on rhizosphere microbiome assembly, predominantly affecting rhizospheric bacteria more than fungi, indirectly influencing soil conditions and plants. Notably, Paenibacillus polymyxa inoculation improved plant nitrogen (by 5.2%) and iron levels (by 28.1%), whereas Bacillus cereus boosted mycorrhization rates (by 70%). Additionally, inoculation led to increased complexity in network interactions within the rhizosphere (~15%), potentially impacting plant health. Overall, the findings highlight the significant impact of introducing bacteria to the rhizosphere, enhancing nutrient availability, microbial diversity, and fostering beneficial plant-microbe interactions.

Introduction: Deforestation of areas for agriculture and cattle breeding is the leading cause of ecological degradation and loss of biodiversity. The solution to mitigate these damages relies on techniques that improve soil health and the microbial quality of these degraded areas. Here, we demonstrate that the high nutrient and microbiological contents of Amazonian Dark Earths (ADE) can promote the development of trees used in ecological restoration projects. Methods: We used degraded soil from crops as control and ADE from the Central Amazon to conduct the experiment, using 20% of ADE as inoculum in degraded agricultural soil. Our goal was to assess whether a small amount of ADE could promote changes that improve plant development similar to its growth under a 100%ADE. We simulated conversion from pasture to forest restoration area by planting U. brizantha in all pots. After 60 days, we removed it and planted Cecropia pachystachya, Peltophorum dubium, and Cedrela fissilis. Results: Our results demonstrated that both 20%ADE and 100%ADE treatments increased pasture productivity and, consequently, soil carbon stock. Also, in these treatments, P. dubium and C. fissilis had better growth and development, with 20%ADE plants showing a performance similar to those planted in 100%ADE. Both 20%ADE and 100%ADE showed similar numbers of taxa, being significantly higher than in the control soil. Discussion: The 20%ADE was sufficient to increase significantly the microbial richness in the soil, providing several beneficial microorganisms to all tree species such as Pedomicrobium, Candidatus Nitrososphaera, and members of Paenebacillaceae. Nevertheless, C. pachystachya, a common pioneer tree in the Amazonian Forest showed a small response even to 100%ADE with a corresponding lower taxa number than the other two species. In conclusion, we point out that microbial structure remains very similar among plants but dissimilar among treatments, highlighting the role of ADE as an enhancer of plant development and beneficial microbiota enrichment in the rhizosphere. The use of 20%ADE was sufficient to alter the microbial community. Therefore, we believe our data could contribute to speeding up forest restoration programs by adopting new biotechnological approaches for forest restoration ecology.

The advancement of forest formations into savannas is a global phenomenon. In recent decades, woody encroachment has been frequent in the state of São Paulo, and several areas previously classified as woodland savanna are now considered ecotones between woodland savanna and semideciduous seasonal forest. One of the possible factors for this phenomenon is the increase in canopy cover provided by typical forest and generalist species, restricting the occurrence of savanna species that require greater sunlight exposure. Canopy cover estimation refers to the amount of area covered by tree canopies in a vegetation area and is crucial for assessing sunlight availability in the ecosystem. Our aim was to determine whether the canopy cover index in a transition area between woodland savanna and semideciduous seasonal forest affects the richness and abundance of the tree community. We measured the abundance of savanna, forest, and generalist species, as well as the average canopy cover during the dry and rainy seasons, in 50 permanent plots in a transition area between woodland savanna and semideciduous seasonal forest, located in Glebe II of the Aimorés Wildlife Refuge, in Bauru, middle-west region of São Paulo state, southeastern Brazil. Multivariate analyzes of correlation, regression, and clustering did not indicate significant results between average canopy cover and the richness and abundance of savanna species. However, we observed strong positive and negative correlations within the tree community, which may indicate a dynamic process of savanna species replacement. Woody encroachment in savanna regions has been widespread among the scientific community. However, the reasons for this phenomenon have not yet been elucidated. It is likely that several factors play a role in woody encroachment, and the main challenge lies in determining the influence of these factors and understanding the degree of interaction among them.