Estrutura filogenética de comunidades arbóreas ao longo do gradiente de inundação em florestas de água preta na Amazônia central e oriental

Abstract

The igapós are flooded regions formed by rivers with black or clear waters, standing out for their low floristic diversity and high endemism. In this study, we used metrics of diversity and phylogenetic structure to investigate the evolutionary history of species and analyze the processes influencing the organization of plant communities. We analyzed the phylogenetic structure of two blackwater forests along the annual flooding gradient, in the Central Amazon (Chapter 1) and the Eastern Amazon (Chapter 2). We utilized a database of floristic inventories and hydrology collected as part of the Riparian Network project in 2018, focusing on the Abacate River in the Sustainable Development Reserve of Uatumã (RDSU) and the Falsino River in the National Forest of Amapá (FLONA do Amapá). Both rivers have headwaters located in the Guiana Shield and formed in different geological times. In each study area, we assessed nine plots of 0.5 hectares (100 m x 50 m), subdivided into eight subplots of 25 m x 25 m. From the list of collected species in the two sub-basins, we created a presence-absence matrix and generated a phylogeny using the largest available database for vascular plants (GBOTB - GenBank taxa with a back provided by One Tree of Life). We used species richness metrics as proportions of the total number of species in each plot. We calculated standardized values for phylogenetic diversity metrics (ses.PD), mean phylogenetic distance (ses.MPD), and mean nearest taxon distance (ses.MNTD) to test whether the relationship history among community species is influenced by flooding. Additionally, we used the phylogenetic endemism metric (PE) to check for branches in the phylogeny representing taxa with restricted spatial distribution.Simple linear regressions were employed to test whether the three standardized phylogenetic metrics (ses.PD, ses.MPD, and ses.MNTD) were significantly related to the variables: (1) maximum flood height, (2) maximum water table depth, and (3) maximum flood extent.Significant effects related to diversity and phylogenetic structure were observed in the two analyzed sub-basins. The results indicate that flood height and extent act as determining factors in the phylogenetic structure of Abacate River forests (Central Amazon), where a portion of riparian forests showed phylogenetic clustering, and a portion of the igapó revealed higher phylogenetic diversity.In the Falsino River (Eastern Amazon), maximum water table depth emerged as a phylogenetic structuring factor in the analyzed communities, where riparian forests are phylogenetically dispersed and more diverse compared to other areas.In general, areas subject to seasonal flooding exhibited not only a reduction in taxon richness but also low phylogenetic diversity and a random distribution of lineages in communities in both sub-basins. Both sub-basins presented areas housing a set of species with branches of restricted spatial distribution, indicating the absence of close relatives in the community. The highest average phylogenetic endemism was observed in the Falsino River, which also demonstrated higher phylogenetic diversity and older geological formation compared to the Abacate River.Despite both rivers belonging to the same typology of flooded areas associated with blackwater rivers, we conclude that these differences reflect the geomorphological history of the sub-basins.