Heterotrophic nitrification of organic nitrogen is stimulated by agricultural plants

The association between soil heterotrophic nitrification and plant nitrogen (N) uptake remains poorly understood. Here, we used 15N isotope tracing and numerical analysis to quantify the rate of ammonification (organic N to ammonium), heterotrophic nitrification (organic N to nitrate) and autotrophic nitrification (ammonium to nitrate) in soils, based on 104 lab observations across 11 plant species. Our results showed that plant cultivation stimulated heterotrophic nitrification, while suppressing autotrophic nitrification, with effects varying by species and N preference. However, this stimulation disappeared rapidly after plant removal. Heterotrophic nitrification was strongly driven by labile substrates and positively associated with plant N uptake. In contrast, autotrophic nitrification, which was pH-driven, was negatively correlated with plant N uptake. Structural equation modeling further revealed that heterotrophic nitrification and ammonification promote total plant N acquisition. Plant-driven stimulation of heterotrophic nitrification demonstrates a critical mechanism by which plant-soil interactions regulate N cycling.