Topsoil and subsoil bacterial community assemblies across different drainage conditions in a mountain environment

Abstract

Background High mountainous environments are of particular interest as they play an essential role for life and human societies, while being environments which are highly vulnerable to climate change and land use intensification. Despite this, our knowledge of high mountain soils in South America and their microbial community structure is strikingly scarce, which is of more concern considering the large population that depends on the ecosystem services provided by these areas. Conversely, the Central Andes, located in the Mediterranean region of Chile, has long been studied for its singular flora, whose diversity and endemism has been attributed to the particular geological history and pronounced environmental gradients in short distances. Here, we explore soil properties and microbial community structure depending on drainage class in a well-preserved Andean valley on the lower alpine vegetation belt (~2500 m a.s.l.) at 33.5˚S. This presents an opportunity to determine changes in the overall bacterial community structure across different types of soils and their distinct layers in a soil depth profile of a highly heterogeneous environment. Methods Five sites closely located (<1.5 km) and distributed in a well preserved Andean valley on the lower alpine vegetation belt (~2500 m a.s.l.) at 33.5˚S were selected based on a pedological approach taking into account soil types, drainage classes and horizons. We analyzed 113 soil samples using high-throughput sequencing of the 16S rRNA gene to describe bacterial abundance, taxonomic composition, and co-occurrence networks. Results Almost 18,427 Amplicon Sequence Variant (ASVs) affiliated to 55 phyla were detected. The bacterial community structure within the same horizons were very similar validating the pedological sampling approach. Bray-Curtis dissimilarity analysis revealed that the structure of bacterial communities in superficial horizons (topsoil) differed from those found in deep horizons (subsoil) in a site-specific manner. However, an overall closer relationship was observed between topsoil as opposed to between subsoil microbial communities. Alpha diversity of soil bacterial communities was higher in topsoil, which also showed more bacterial members interacting and with higher average connectivity compared to subsoils. Finally, abundances of specific taxa could be considered as biological markers in the transition from topsoil to subsoil horizons, like Fibrobacterota, Proteobacteria, Bacteroidota for shallower soils and Chloroflexi, Latescibacterota and Nitrospirota for deeper soils. Conclusions The results indicate the importance of the soil drainage conditions for the bacterial community composition, suggesting that information of both structure and their possible ecological relationships, might be useful in clarifying the location of the edge of the topsoil-subsoil transition in mountainous environments.

Evaluating Bacterial Population Changes and Ecological Dynamics in Oil-Impacted Soils Using 16S rRNA Amplicon Sequencing

“…Soil bacterial diversity is known to be in uenced by changes in the environmental physico-chemical factors such as temperature, pH, water content, nutrients, texture, and vegetation types. ( (Mhete, et al 2020;Aguado-Norese, et al 2023). In this study, we observed high diversity and variation both within and across different treatment groups and depths, highlighting the complexity of the soil samples.…”

Rising awareness to improve conservation of microorganisms in terrestrial ecosystems: advances and future directions in soil microbial diversity from Chile and the Antarctic Peninsula

“…Therefore, soil microbial diversity can only be fully understood through the integration with these connected disciplines. Despite some efforts to combine soil microbial diversity and geochemical data (e.g., Mandakovic et al, 2018;Aponte et al, 2022;Barret et al, 2022;Aguado-Norese et al, 2023), integrated studies are scarce. As an example, in our survey the type of soil was rarely explicitly indicated, despite the great diversity of soil orders identified in Chile (Casanova et al, 2013).…”