Comparative Analysis of Soil Metagenomes from North- and South-facing Slopes

Abstract

The purpose of this study was to compare soil microbial composition between north- and south-facing slopes in a chaparral ecosystem. Sampling took place in January 2025 on the CSUSM Campus, where two 50-meter-long transects were randomly placed on each slope. From each baseline, five branch lines were randomly placed along every 50-meter transect using a random number generator. The first random number determined whether the branch line was going to be upslope or downslope, while the second random number determined the length of each branch line. Soil samples were collected from the drip line of two species known as Salvia mellifera and Ceanothus tomentosus, and DNA was extracted for metagenomic analysis. There were significant differences in alpha diversity observed between the two slope types, with south-facing slopes showing higher Shannon diversity (p < 0.05). However, there were no significant differences found in Simpson diversity (p > 0.05). Beta diversity analysis showed distinct microbial communities, which were influenced by the slope direction (PERMANOVA & ANOSIM, p = 0.001). Our results indicated that South-facing slopes had a higher differential abundance of radio-tolerant bacteria. Canonical Correspondence Analysis (CCA) revealed that environmental influences, pH and nitrogen, were the strongest drivers on microbial community composition. The total nitrogen had an impact on north-facing slopes, while ammonia concentrations south-facing slopes. Overall, this study highlights how slope aspect strongly affects soil microbial diversity and community composition.