The carbon sink of tropical seasonal forests in southeastern Brazil can be under threat

Tropical forests have played an important role as a carbon sink over time. However, the carbon dynamics of Brazilian non-Amazon tropical forests are still not well understood. Here, we used data from 32 tropical seasonal forest sites, monitored from 1987 to 2020 (mean site monitoring length, ~15 years) to investigate their long-term trends in carbon stocks and sinks. Our results highlight a long-term decline in the net carbon sink (0.13 Mg C ha−1 year−1) caused by decreasing carbon gains (2.6% by year) and increasing carbon losses (3.4% by year). The driest and warmest sites are experiencing the most severe carbon sink decline and have already moved from carbon sinks to carbon sources. Because of the importance of the terrestrial carbon sink for the global climate, policies are needed to mitigate the emission of greenhouse gases and to restore and protect tropical seasonal forests.

Paleoenvironmental changes in the Hiwegi Formation (lower Miocene) of Rusinga Island, Lake Victoria, Kenya

The Early Miocene of Rusinga Island (Lake Victoria, Kenya) is best known for its vertebrate fossil assemblage—particularly of early hominoids and catarrhines—but the multiple stratigraphic intervals with well-preserved fossil leaves have received much less attention. The Hiwegi Formation has three fossil leaf-rich intervals: Kiahera Hill, R5, and R3. Here, we made new fossil collections from Kiahera Hill and R3 and compared these floras to previous work from R5 as well as modern African floras. The Kiahera Hill flora was most similar to a modern tropical rainforest or tropical seasonal forest and was a warm and wet, closed forest. This was followed by a relatively dry and open environment at R5, and R3, which was most similar to a modern tropical seasonal forest, was a warm and wet spatially heterogenous forest. Floral composition of these floras differed dramatically but Kiahera Hill and R3 were more similar to each other than either flora was to R5. The Kiahera Hill flora had few monocots or herbaceous taxa and was dominated by large leaves and had a higher species richness and greater evenness than the R3 flora. Our work, coupled with previous studies, suggests that R3 had a landscape of both closed forest and more open areas with seasonal ponding. The absence of morphotypes from the R5 flora that were present in the Kiahera Hill and R3 floras provides evidence for local expatriation during the R5 time interval. These results demonstrate that there was a considerable change in both climate and vegetation over an ~500 kyr interval of the Kiahera Hill, R5, and R3 floras. Thus, this work suggests that the Hiwegi Formation on Rusinga Island samples multiple environments in the Early Miocene and provides important context for the evolution and habitat preference of early apes.

USING Next-Generation Sequencing (NGS) TO UNCOVER DIVERSITY OF WOOD-DECAYING FUNGI IN NEOTROPICAL ATLANTIC FORESTS

A targeted amplicon-based metagenomics approach (metabarcoding) provides detailed access to the diversity of the mycobiome in any substrate in distinct environments on Earth. Fungi are the main decomposers of lignocellulosic woody debris in terrestrial forested ecosystems, contributing significantly to the global carbon cycle. The main objectives of this study were to assess the fungal taxonomic diversity in fallen woody debris samples from two Neotropical forest fragments (rainforest and seasonal forest), to analyze the qualitative and quantitative components of the taxonomic diversity, and to investigate the functional diversity of the ecological groups detected. Our study comprised three main methodological steps: (i) sampling in the field; (ii) extraction of DNA, amplification of targeted segments and massively parallel sequencing; and (iii) data analysis and interpretation. A total of 110 molecular operational taxonomic units showing sequence similarity of 95% or more across the two collection sites using two DNA metabarcoding markers (ITS1 and ITS2) were assigned to putative fungal genera in 59 families, 27 orders, and 3 phyla. The number of putative fungal genera and the relative abundance of reads for each genus are higher in the tropical rainforest site than in the tropical seasonal forest site. Most of the identified genera are ligninolytic and cellulolytic and/or hemicellulolytic Basidiomycota (Agaricomycetes) and Ascomycota (Sordariomycetes), but “sugar fungi” and fungi associated with plants and detritivorous insects were also detected. This is the first study using NGS as a rapid and large-scale useful strategy to uncover the diversity of wood-decaying fungi in tropical forests.