Effects of tree species identity on soil microbial communities in Juglans nigra and Quercus rubra plantations.

Black walnut (Juglans nigra L.) forestry within the Central Hardwoods Region (CHR) has progressed primarily based on studies of trial and error among plantations. Although J. nigra wood has been used for everything from gunstocks in the Revolutionary War to the artfully crafted furniture of today, gaps exist in our knowledge base regarding the impact of this hardwood species on the soil. We aim to evaluate and analyze how J. nigra modified soil bacterial and fungal structure in conjunction with soil properties after 10 years of establishment. Additionally, we used another hardwood tree Northern red oak (Quercus rubra L.) for contrast. Our results showed soil microbial structure is influenced primarily by plant species; then by season, and lastly depth. The alpha-diversity index was increased in J. nigra compared to bulk soil values, whereas Q. rubra decreased the index. The most significant disparities in microbiomes were observed between plant species with J. nigra displaying greater enrichment in Nitrospira, Geobacter, Steroidobacter, Bacillus, and Perlucidibaca while Q. rubra more enriched in Acidobacteria (GP1, GP2, and GP3) and ectomycorrhizal fungi (Tuber, Inocybe, Amanita, and Russula). Finally, the co-occurrence networks showed that J. nigra increased node numbers while Q. rubra increased connection (edge) numbers. Additionally, the Q. rubra network displayed the highest mean degree, density, and clustering coefficient while J. nigra exhibited the highest modularity and average connectivity. In conclusion, our findings highlight the intricate interplay between CHR tree species and soil microbiota.