Rhizobiota links landsliding and the carbon cycles through rock weathering

Landslides set in motion biogeochemical processes that are not yet conceptually linked. The microbial communities growing on the root surfaces, i.e. the rhizobiome, of plants colonizing landslides can accelerate the release of nutrients from newly exposed rocks through rock weathering. The release of (Ca, Mg) from silicate rocks is important for their role in the carbon cycle. We hypothesize that rhizobiomes in areas underlain by (Ca, Mg)-bearing silicate rocks represent an important link between processes affecting short- and long-term carbon cycling. To test this hypothesis, we examined the composition and function of rhizobiomes in the context of a field incubation experiment with the aim of answering two questions: 1) How does the composition and function of rhizobiomes in landslides change over time? and 2) Is there a relationship between rock weathering and the taxonomic and functional diversity of rhizobiomes? The experiment was conducted around tree ferns (Cyanthea) in areas with granodiorite bedrock in the Central Mountains of Puerto Rico. The experiment included four factors: two abiotic [habitat (landslides, undisturbed forest) and substrate (granodiorite tiles, pressed pellets)] and two biotic [microhabitat (rhizosphere, bulk soil) and root/fungal hyphal activity (mesh size that allows or restricts root access)]. The experiment was replicated spatially (four hosts per habitat) and temporally (7- and 48-month retrievals). We extracted DNA and sequenced the 16S-V4 region of the experimental units at two time points. We identified microbial species belonging to 54 16S phyla using the GreenGenes2 taxonomy and 14 ITS phyla using the UNITE taxonomy. Most bacteria belonged to ten phyla [Proteobacteria, Acidobacteriota, Planctomyceota, Verrucomicrobiota, Actinobacteriota, Bacteroidota, Chloroflexota, Myxococcota_A, Methylomirabilota, and Desulfobacterota_B], while most Archaea belonged to one phyla [Thermoproteota] and most fungi to 4 phyla [Ascomycota, Basidiomycota, Morterellomycota and Chyrtidiomycota]. The microbial communities changed in abundance and species richness over time. The abundance of four phyla increased over time [Planctomyceota, Chlamydiota, Thermoproteota, Firmicutes_D,] and that of three decreased [Bacteriodota, Armatimonadota and Cyanobacteria]. Finally, the species richness of bacteria and archaea increased over time, while the species richness of fungi increased, decreased, or remained constant depending on the substrate. This experiment will help to clarify the relationships between the taxonomy and functioning of rhizobiomes and biogeochemical processes.