Impact of Farming System on Soil Microbial Communities Associated with Common Bean in a Region of Northern Spain

Agricultural soil microbiomes play a crucial role in the modification and maintenance of soil properties such as soil fertility, nutrient availability, and organic matter decomposition. This study assessed the influence of organic and conventional farming practices on soil microbiomes associated with common bean (Phaseolus vulgaris L.) at the field scale in Northern Spain. Metabarcoding techniques were used to compare both microbial communities. Alpha and beta diversity analyses revealed that organic soils supported richer fungal communities with a higher species evenness, whereas conventional soils were abundant in prokaryotes. Taxonomic assignment of the observed Operational Taxonomic Units (OTUs) identified a total of 1141 prokaryotic and 622 fungal taxa. Among these, 200 prokaryotic and 113 fungal OTUs showed significant differences in response to different farming practices. This classification allowed the establishment of a core microbial community associated with the common bean crop, comprising 594 prokaryotic OTUs classified into 11 phyla, and 256 fungal OTUs classified into 11 phyla. Functional analyses indicated that organic farming promoted a broader range of prokaryotic functions related to nitrogen metabolism, stronger positive interactions between fungi and bacteria, a higher abundance of beneficial microorganisms, such as biocontrol fungi and mycorrhizae, and greater overall microbial stability. In contrast, conventional soil showed a higher prevalence of potentially phytopathogenic fungi and more complex, competitive microbial interactions. These results highlight the effect of the farming system on the diversity and microbial composition of the soils associated with bean crops in Northern Spain. While further research in different climatic regions and crop systems is essential, these findings underscore the potential of organic farming to improve soil diversity and enhance microbial network interactions.