Relationships between color and bacteria in Mediterranean soil environments

Soil color has long been used as an index of other soil characteristics, but its relationship to soil bacteria has not yet been thoroughly investigated. We study this in three Mediterranean environments with 113 soil sampling sites in southern Spain. CIELAB color parameters were correlated with soil components and properties, as well as with the abundance of many bacterial taxa and KEGG functional pathways. The analysis of co-occurrence networks revealed that bacterial communities were linked to specific soil colors. Linear discriminant analysis effect size detected enriched taxa in soil samples clustered by color similarity with the partitioning around medoids algorithm. The KEGG pathways indicated aromatic-degrading, heterotrophic, and microbial competence profiles in darker soils versus rapid-turnover, carbohydrate-focused, and phototrophic/pigment-related metabolic strategies in lighter-colored soils. Within the latter, more biosynthetically active communities appeared in yellowish soils, while stress-tolerant and degradation-oriented communities appeared in reddish soils. The results suggest the existence of bacterial habitats that can be distinguished by soil color. Consequently, soil color can contribute to understanding the ecology of bacteria once they have been identified, providing general guidelines on the bacterial distribution and the molecular mechanisms involved. In short, soil color parameters are associated with the composition and functioning of bacterial communities. Therefore, although not the cause, soil color is an index of bacterial habitat conditions in Mediterranean soils.