Millennium Institute Center for Genome Regulation, Santiago, 7830490, Chile.
Bioinformatic and Gene Expression Laboratory, INTA-Universidad de Chile, Macul, Chile.
Biol Res. 2023 Jun 24;56(1):35. doi: 10.1186/s40659-023-00445-2.
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.
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.
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.
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.
高山环境至关重要，因为它们是生命和人类社会的基础，同时也是对气候变化和土地利用强度高度敏感的环境。尽管如此，我们对南美洲高山土壤及其微生物群落结构的了解却少得惊人，这更令人担忧，因为有大量人口依赖这些地区提供的生态系统服务。相比之下，位于智利地中海地区的中央安第斯山脉因其独特的植物群而长期受到研究，其多样性和特有性归因于特殊的地质历史和短距离内明显的环境梯度。在这里，我们根据排水等级在安第斯山谷的低高山植被带（~2500 米海拔）中探索了土壤特性和微生物群落结构。这为确定在高度异质环境中不同类型土壤及其土壤深度剖面中不同层的整体细菌群落结构变化提供了机会。
根据土壤类型、排水等级和土层考虑的土壤学方法，在 33.5˚S 处低高山植被带（~2500 米海拔）的一个保存完好的安第斯山谷中选择了五个紧密相邻（<1.5 公里）的地点。我们使用 16S rRNA 基因高通量测序分析了 113 个土壤样本，以描述细菌丰度、分类组成和共生网络。
检测到近 18427 个属于 55 个门的扩增子序列变异（ASV）。同一土层内的细菌群落结构非常相似，验证了土壤学采样方法的有效性。Bray-Curtis 不相似性分析表明，在特定地点，表层（表土）的细菌群落结构与深层（底土）的细菌群落结构不同。然而，与底土微生物群落相比，表土之间的关系更为密切。表土的土壤细菌群落的 alpha 多样性较高，与底土相比，表土中的细菌成员之间的相互作用更多，平均连接性更高。最后，特定类群的丰度可以被视为从表土到底土过渡的生物标志物，如拟杆菌门、变形菌门、浮霉菌门等较浅土壤，以及 Chloroflexi、Latescibacterota 和 Nitrospirota 等较深土壤。
结果表明土壤排水条件对细菌群落组成的重要性，表明结构及其可能的生态关系的信息可能有助于阐明山地环境中表土-底土过渡的边缘位置。
