Phytobiomes of the Amazon forest: diversity and functionality of the bacterial communities from the phyllosphere, rhizosphere and litter.

Abstract

In previous studies, we have determined that the bacterial community structures in the phyllosphere of different tree species depend on the plant taxon. We have also determined that despite the different taxonomic composition, most of the detected functional protein groups were common to all phyllospheres examined, suggesting that bacterial communities in different phyllospheres share a set of functional group of proteins necessary for adaptation and survival in such environment. Among the main functions of the microorganisms in the phyllosphere, biological nitrogen fixation (BNF) may have a relevant ecological role. The BNF associated with certain phyllospheres in a preserved area of the Atlantic Forest (AF) may contribute with 80-240 kg N ha-1 year-1, according to our estimates. In some plant species, the BNF rates associated with the phyllosphere and dermosphere together are more than 100 times higher than the BNF rates in the soil. Overall, our data suggest N inputs much higher than those reported in the literature, changing paradigms of N cycling in tropical forests. If the bacterial communities associated with plants in other tropical forests are organized in a similar way to that observed in the AF is not known. Similarly, it is not clear whether the N inputs through BNF in the phyllosphere, litter and rhizosphere in other tropical forests are similar to that observed in the AF. However, if this process is common in tropical forests, the global N cycle should be revised. To answer these questions, among others, the project "Epiphyllic communities on leaves at tropical forests: causes and consequences for leaf functioning at different scales", coordinated by Prof. Dr. Bruno Rosado (UERJ) and Prof. Dr. Rafael Oliveira (UNICAMP), and funded by USAID (PEER Science Cycle 2, Grant # 515) is being carried out. In this project, various functional characteristics of the leaves of different tree species of the Amazon Forest (AF) are being evaluated and will be used to determine their possible effects on the structure and function of bacterial communities in phyllosphere. However, we would like to expand the microbiome analyses, sampling a higher number of tree species and individuals, in relation to what was performed in the AF, since one of the major criticisms of our work is the limited number of samples as compared to the current standards for microbiome studies. Our project contemplates collecting samples at three different time points, of which two have been concluded. Leaf, litter and rhizosphere samples of approximately 10 individuals of 9 tree species, comprising a total of 90 samples of each compartment, have been collected in the Km 67 experimental station of the Tapajós National Forest. BNF rates in the phyllosphere, litter and rhizosphere have been determined in situ. Total DNA of each sample has been extracted and is being prepared for sequencing of the bacterial 16S rRNA and nifH genes. Comparative analyses of 810 bacterial communities will be performed. However, our project does not include resources for the analyses at the required depth. As far as we know, this is the first study of this kind to be held on fitobiomes of the AF. The information on the bacterial and diazothrophic community structures and environmental variables will be analyzed using artificial neural networks to identify the factors and the main groups of bacteria determining community assembling, as well as their possible roles in ecosystem functioning, and N input via BNF. Studies on plant associated microbiomes in the AF are scarce and may contribute to a better understanding of the ecology of microorganisms and nutrient cycling in this biome, having a global impact on ecosystem studies. (AU)