Soil Microbiome Beta, Taxonomic and Functional Diversity in British Columbian Logged Douglas-Fir Stands Differs Across the A and O Horizon

Abstract

Soil bacterial composition varies based on a wide variety of factors and is responsible for much of soil nutrient cycling. To date, the correlations between microbial community composition, functional potential and different soil layers or horizons are not well studied. We investigated the top two organic soil layers, the A horizon and O horizon, in sites of logged British-Columbian Douglas-fir trees and their correlations with microbial diversity. We investigated microbial diversity through alpha diversity, beta diversity and core microbiome analyses. Additionally, we aimed to characterize the microbiota through indicator taxa analysis and PICRUSt2 analysis to determine specific taxonomic and functional differences between the horizons. We found no significant differences in alpha diversity across the A and O horizons whereas in our beta diversity analyses we found clustering within each respective horizon. Furthermore, core microbiome investigations revealed some overlap at the genus level along with greater taxonomic diversity in the O horizon. We also found differences in the top indicator taxa for each horizon using indicator taxa analyses. This was further supported by functional pathway analysis. 407 MetaCyc functional pathways were significantly differentially abundant between horizons, indicating distinct functional niches. These results affirm the clear differences between the microbial diversity and community composition in the A and O horizons, indicating the need for more microbial diversity research regarding horizon depth and logged soil. This will hence improve our understanding of microbial community formation and the potential impact of environmental and human-made factors.