Format: ORAL

Allie Igwe1, Michelle Afkhami1

1 Department of Biology, University of Miami, Miami, USA

Serpentine soils, characterized by high heavy metal levels and magnesium-to-calcium ratios, exert selective pressure on plants and microorganisms. While some plants are endemic to these soils, most struggle to survive. Our research revealed that serpentine-indifferent plants, thriving on both serpentine and non-serpentine soils, may be sustained by their association with locally adapted plant growth-promoting bacteria. The role of microorganisms in supporting plant diversity and ecosystem services is being explored, and characterizing taxonomic and functional microbe diversity on and off serpentine soils is crucial. Our project aimed to identify taxa associated with serpentine or nonserpentine soils, characterizing microorganisms plant-growth-promoting properties across California. Shotgun metagenomic sequencing and physiological assays were conducted on soil samples from 23 sites. Kaiju and MEGAN6 were used for taxonomic classification and functional analysis. After removing contaminants, 41,326 taxa were identified, with similar abundance and alpha diversity across serpentine and nonserpentine soils. Soil chemistry and location significantly shaped bacterial and eukaryotic communities, not archaeal ones. Random forest analysis highlighted features like Mesorhizobium, Rhizobium, and Pontibacter in nonserpentine soils and Nitrosophaera and Pontibacter in serpentine soils. Preliminary functional analysis revealed Ni/Fe subunits and siderophore production functions. Siderophore production was influenced by nickel presence, with higher levels in serpentine soils. Approximately 50% of microorganisms from both soil types fixed nitrogen, and 20% solubilized phosphorus. This study enhances our understanding of nutrient cycling in metal-rich, drought-prone soils, impacting plant-microbe interactions, agriculture, and bioremediation. The findings inform conservation policies, aiding efforts to preserve unique soil ecosystems and their microorganisms.