Acidic soils rapidly retain applied phosphorus fertilizers and consequently present low availability of this nutrient to plants. the use of phosphate-solubilizing microorganisms to help plant phosphorus (P) absorption is a promising sustainable strategy for managing P deficiencies in agricultural soils. Trichoderma strains have been one of the most studied filamentous fungi for improving the production and development of several crop species mainly due to their capability for symbiotic associations and their ability to control soil-borne plant diseases. Thus, this work sought to bioprospect Trichoderma strains from the Amazon rainforest capable of solubilizing/mineralizing soil phosphate and promoting soybean growth. Soybean plants inoculated with selected Trichoderma strains were cultivated in soil under greenhouse conditions and under a gradient of rock phosphate and triple superphosphate. As a result, 19.5% of the isolated Trichoderma strains were able to solubilize phosphate. In addition, those strains produced different organic acids during the solubilization process. Trichoderma spp. strains showed positive responses in the promotion of soybean growth-from 2.1% to 41.1%-as well as in the efficiency of P uptake-up to 141%. These results reveal the potential of Trichoderma spp. from the Amazon biome as promising biofertilizer agents.The high demand for fertilizers used in Brazilian agriculture is a result of the growing population, which necessitates an increase in food production 1 . Brazil is the second-largest supplier of food and agricultural products and expected to be the leading producer of food to meet global demand in the near future 2 . Thus, applications of fertilizer are a routine activity in agricultural production as an attempt to promote crop growth to increase productivity. The requirement of fertilizers in the field results in the accumulation of those inputs in soils and water and, therefore, environmental pollution, causing problems to human and animal health 1,3 . In the future, Brazilian agriculture has to identify alternatives to reduce its dependence on chemical fertilizers while at the same time functioning in a lucrative and more sustainable way 4 .A range of nutrients is important for plant growth 5 , but the ones that limit agricultural production the most are nitrogen and phosphorus, which are important in the initial development of the plant 6,7 . Nitrogen fertilization in Brazil has decreased significantly with use of symbiotic associations with nitrogen-fixing bacteria 8,9 . However, Brazilian agriculture continues to depend on chemical phosphate fertilization 4 . The role of P in the plant is associated with three essential biochemical processes: energy production, respiration, and photosynthesis. P is also involved in enzymatic processes and is a component of nucleic acids and cell membranes [10][11][12][13] . Phosphorus is generally found in the lowest concentration in the soil, 0.01%, compared to 0.14% of nitrogen, mainly in tropical and subtropical regions 14,15 . Although ...

In this study, 16S rRNA gene amplicon sequencing was used to assess bacterial diversity and dynamics throughout different stages of leaves decomposition of three plant species (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) in three distinct mangroves of São Paulo state, Brazil. The experiments were conducted in microcosms. Phylogenetic diversity (Faiths' PD) index showed differences between samples and suggested that some treatments like R. mangle increased their bacterial diversity through time. Principal coordinate analysis revealed that community's profile varied based on mangroves, followed by plant species and time. A clear succession patterns was observed in this study, i.e., some microorganisms with low abundance in the initial phases gradually became dominant (e.g., Alphaproteobacteria), whereas microbes that were initially predominant became low (e.g., Gammaproteobacteria). Co-occurrence analyses were performed for all times of plant degradation aiming to better understand the relationships between bacterial populations. The c-score index was done to test the randomness of the community assemblage during the stages of decomposition. For all degradation time points, the values of the observed c-score were higher than the values of the simulated c-score. This result indicated that during plant decomposition, the bacterial communities presented less co-occurrence than expected by chance and that these communities were not randomly assembled but instead they are driven by species interactions. Network analyses results showed that in the conditions presented in this experiment, the initial stages of leaf decomposition formed more connected and complex networks than the later stages. These results suggest that resource competition was a determinant in these specific mangroves during plant degradation, mainly in the initial periods.

BackgroundMangroves are important coastal ecosystems known for high photosynthetic productivity and the ability to support marine food chains through supply of dissolved carbon or particular organic matter. Most of the carbon found in mangroves is produced by its vegetation and is decomposed in root associated sediment. This process involves a tight interaction between microbial populations, litter chemical composition, and environmental parameters. Here, we study the complex interactions found during litter decomposition in mangroves by applying network analysis to metagenomic data.MethodsLeaves of three species of mangrove trees typically found in the southeast of Brazil (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) were collected in separate litter bags and left on three different mangroves for 60 days. These leaves were subsequently used for metagenome sequencing using Ion Torrent technology. Sequences were annotated in MG-RAST and used for network construction using MENAp.ResultsThe most common phyla were Proteobacteria (classes Gamma and Alphaproteobacteria) followed by Firmicutes (Clostridia and Bacilli). The most abundant protein clusters were associated with the metabolism of carbohydrates, amino acids, and proteins. Non-metric multidimensional scaling of the metagenomic data indicated that substrate (i.e., tree species) did not significantly select for a specific community. Both networks exhibited scale-free characteristics and small world structure due to the low mean shortest path length and high average clustering coefficient. These networks also had a low number of hub nodes most of which were module hubs.DiscussionThis study demonstrates that under different environmental pressures (i.e., plant species or mangrove location) the microbial community associated with the decaying material forms a robust and stable network.

Leaf decomposition is the primary process in release of nutrients in the dynamic mangrove habitat, supporting the ecosystem food webs. On most environments, fungi are an essential part of this process. However, due to the peculiarities of mangrove forests, this group is currently neglected. Thus, this study tests the hypothesis that fungal communities display a specific succession pattern in different mangrove species and this due to differences in their ecological role. A molecular approach was employed to investigate the dynamics of the fungal community during the decomposition of three common plant species (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) from a mangrove habitat located at the southeast of Brazil. Plant material was the primary driver of fungi communities, but time also was marginally significant for the process, and evident changes in the fungal community during the decomposition process were observed. The five most abundant classes common to all the three plant species were Saccharomycetes, Sordariomycetes, Tremellomycetes, Eurotiomycetes, and Dothideomycetes, all belonging to the Phylum Ascomycota. Microbotryomycetes class were shared only by A. schaueriana and L. racemosa, while Agaricomycetes class were shared by L. racemosa and R. mangle. The class Glomeromycetes were shared by A. schaueriana and R. mangle. The analysis of the core microbiome showed that Saccharomycetes was the most abundant class. In the variable community, Sordariomycetes was the most abundant one, mainly in the Laguncularia racemosa plant. The results presented in this work shows a specialization of the fungal community regarding plant material during litter decomposition which might be related to the different chemical composition and rate of degradation.

Microbial communities regulate nutrient cycling in soil, thus the impact of climate change on the structure and function of these communities can cause an imbalance of nutrients in the environment. Structural and functional changes of soil bacterial communities in two contrasting biomes in Brazil, the Atlantic Forest and the Tropical Dry Forest (Caatinga), were studied by simulating, in microcosms, rainfall and drought events. Soil samples were collected in three Brazilian states: Bahia, Pernambuco and São Paulo, in a total of four sampling sites. Analysis of 16S rRNA amplicon libraries revealed changes in microbial communities after three drying-rewetting cycles (60-30% water holding capacity). Alpha diversity indexes were obtained for bacterial communities, as well as the functional diversity index (Shannon) based on the activity of the following enzymes: acid and alkaline phosphatase, arylsulfatase, dehydrogenase, cellulase, amylase, urease and phytase. In general, the soils of Caatinga showed a decrease in the diversity indexes studied, conversely, however, the soils of Atlantic Forest were found to be more resistant during the drying-rewetting cycles. Functional diversity was significantly different for the two biomes, with a decrease in Caatinga soils, while Atlantic Forest samples demonstrated a greater stability of enzymatic activity. Further, the Atlantic Forest samples showed more resistance when compared to samples from Caatinga. The results found in this study have confirmed the hypothesis that biomes, independent of climate, when subjected to successive events of drought and rewetting exhibit structural and metabolic changes.

Mangroves are dynamic and unique ecosystems that provide important ecological services to coastal areas. The phylloplane is one of the greatest microbial habitats, and most of its microorganisms are uncultivated under common laboratory conditions. Bacterial community structure of Laguncularia racemosa phylloplane, a well-adapted mangrove species with salt exudation at foliar levels, was accessed through 16S rRNA amplicon sequencing. Sampling was performed in three different sites across a transect from upland to the seashore in a preserved mangrove forest located in the city of Cananéia, São Paulo State, Brazil. Higher bacterial diversity was observed in intermediary locations between the upland and the seashore, showing that significant intraspecific spatial variation in bacterial communities exists between a single host species with the selection of specific population between an environmental transect.

Mangroves are dynamic and unique ecosystems, that provide important ecological services to coastal areas. The phylloplane is one of the greatest microbial habitats and most of its microorganisms are uncultivated under common laboratory conditions. Bacterial community structure of Laguncularia racemosa phylloplane, a well-adapted mangrove species with salt exudation at foliar levels, was accessed through 16S rRNA amplicon sequencing. Sampling was performed in three different sites across a transect from upland to the seashore in a preserved mangrove forest located in the city of Cananéia, São Paulo state, Brazil. Higher bacteria diversity was observed in intermediary locations between the upland to the seashore, showing that exists significant intraspecific spatial variation in bacteria communities between a single host species with the selection of specific population between an environmental transect

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