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.

土壤异养硝化作用与植物氮（N）吸收之间的关联迄今仍未得到充分阐明。本研究借助15N同位素示踪技术与数值分析方法，基于覆盖11种植物的104组室内观测数据，定量解析了土壤中氨化作用（有机氮转化为铵态氮）、异养硝化作用（有机氮转化为硝态氮）以及自养硝化作用（铵态氮转化为硝态氮）的反应速率。研究结果表明，植物种植可促进土壤异养硝化作用，同时抑制自养硝化作用，且该调控效应因植物物种与氮偏好类型而异。但当移除种植的植物后，这种促进作用会快速消失。异养硝化作用主要受易分解底物驱动，且与植物氮吸收呈显著正相关；与之相反，受pH条件调控的自养硝化作用则与植物氮吸收呈显著负相关。结构方程模型进一步揭示，异养硝化作用与氨化作用可共同促进植物总氮获取。植物驱动的异养硝化作用促进效应，揭示了植物-土壤相互作用调控氮循环的关键机制。