Beneficial Cowpea Associated Microbial Communities are Shaped by Crop History and Soil Nutrients

Microbial communities indigenous to crop fields- particularly root-nodulating rhizobia – enhance growth and yield of legume crops, but the magnitude of microbial effects and their drivers are poorly understood. We sampled cultivated soils across a 1000km transect in California focusing on ten sites with recent cowpea cultivation. Grower practices and crop histories were analyzed, and soils were characterized for resident microbial communities and physiochemical features. Live soil inocula were created from each of the field soils to test the capacity to induce root nodulation and growth effects to six legume cultivars, including cowpea, soybean, and lima- selected because they associate with root-nodulating Bradyrhizobium. Soil inoculations influenced host growth response, which was largely positive to cowpeas on average, but varied depending on soil source and cowpea genotype. Soybean and lima showed little compatibility with root-nodulating rhizobia resident to cowpea fields. Soil source, plant genotype, and soil-plant interactions all impacted variation in plant growth, nodule counts and nodule mass. Crop history and plant genotype were primary factors influencing plant-soil interactions, suggesting a primacy of host plants in reshaping resident soil microbial communities. Links between soil physiochemical features, resident microbial communities, and plant performance offer novel routes to manipulate soils towards improved crop yields.