Micronutrients modulate the structure and function of soil bacterial communities

Soil micronutrients are increasingly recognized as critical regulators of biogeochemical cycling and terrestrial ecosystem processes. Despite substantial efforts establishing how belowground microbial communities respond to macronutrients such as N and P, responses to micronutrients remain poorly understood. This is of particular interest in tropical soils, where micronutrients are heterogeneously distributed and often deficient. Using nearly 300 soil samples that span broad gradients in soil micronutrients, we aimed to determine how differences in micronutrients (Ca, Mg, S) and secondary macronutrients (Mn, Fe, Zn) shape soil bacterial communities and their metabolic capabilities. Along with key soil parameters including pH and climatic predictors, we found that Ca, Mg, and Mn were important in shaping the composition and function of soil microbiomes. We also identified lineages that were consistently responsive to specific micronutrients, with those taxa found in low micronutrient conditions often associated with oligotrophic life history strategies. We detected a subset of metabolic attributes related to nutrient cycling that were strongly associated with specific micronutrients. Notably, Mn was important in predicting the abundance of gene systems related to P metabolism including control of Pho regulon and alkylphosphonate utilization, suggesting that it may be important mediators of these responses. Taken together, our results begin to establish a broader understanding of the extent to which belowground systems are shaped by micronutrients and the strategies that soil microbes employ in variable micronutrient environments.