Geoderma (Nov 2023)
Unraveling the importance of top-down predation on bacterial diversity at the soil aggregate level
Abstract
The soil microbiome is dynamically structured at the local soil aggregate level by a combination of bottom-up and top-down processes. The soil microbiome is structured at the local soil aggregate scale by a dynamic interplay of bottom-up and top-down processes, yet less attention has been given to the latter (e.g., predation). We aimed to identify distinct groups of predators (protists and nematodes) and prey (bacteria) to determine the effect of predation on microbial gene abundances associated with carbon and nitrogen metabolisms. We partitioned soil aggregate size at three distinct levels to distinguish potential differences in predator–prey microbe interactions that take place at the soil micro-structure level. Our results revealed that the bacterial diversity and the abundance of protists were significantly higher in microaggregates than in macroaggregates. Correlation analysis, structural equation modeling, and co-occurrence networks suggested that predation by protists and nematodes impacted the diversity (Shannon index) and stability (average variation degree) of soil bacterial community, with a more pronounced effect on the bacterial community in soil macroaggregates than in smaller microaggregates. Compared to microaggregates, the higher frequency of predation within macroaggregates was found to promote faster microbiome turnover with direct implications for the abundance of genes involved in carbon and nitrogen metabolisms. Lastly, we also studied the importance of predation as a mechanism promoting bacterial diversity using field and microcosm studies, with a specific focus on the dominant bacterivorous nematode Protorhabditis. We addressed the influence of top-down processes on soil microbiome diversity and modulation of the genetic potential of genes involved in carbon and nitrogen metabolisms. Our study provides evidence for the importance of predation impacting the diversity and stability of soil bacterial communities. In addition, it shows that predation alters the abundance of microbial genes associated with carbon and nitrogen metabolisms at the soil aggregate level.
