Root exudation of organic acid anions and recruitment of beneficial actinobacteria facilitate phosphorus uptake by maize in compacted silt loam soil

Soil compaction restricts root growth and plant nutrient uptake, but the effects on the abundance and diversity of soil microbiome are poorly understood. A field study with maize (Zea mays L.) was conducted with two soil-compaction treatments (NC: non-compacted; C: compacted) to investigate the interactions of root exudates and microorganisms and the effect on P uptake at two growth stages (seedling and flowering). At the seedling stage, shoot P concentration was decreased by 13.7% in the C treatment compared with the NC. Root growth and arbuscular mycorrhizal fungi colonization were reduced probably due to the decreased soil porosity after compaction. However, root organic acid anions (OAAs) levels were increased by 170%. Several genera of actinobacteria were specifically enriched in the rhizosphere and their abundance was significantly correlated with the concentration of OAAs. However, the positive correlations of concentration of OAAs and abundance of microorganisms or plant P uptake were not observed at flowering stage. Our results indicated that besides the well-known function of exuded organic acid anions on soil P mobilization, maize might also select for microorganisms associated with the facilitation of P acquisition, and mitigating P deficiency at the early growth stage of the plant in compacted soil.