Elucidation of the interplay between roots and microorganisms in the organic N transformation in the rhizosphere of maize

Mechanisms of nitrogen (N) acquisition in the rhizosphere often include microbial immobilization of mineral N and its further transformation into organic compounds. Therefore, visualization and quantification of organic N distribution and their correlation with N-related enzymatic hotspots helps to reveal the role of roots in plant-microbial interplay related to N cycling. In this study, time-lapse leucine aminopeptidase (LAP) zymography and amino-mapping were coupled to reveal amino-N distribution both in the soil and distinct root segments of Zea mays L. A strong overlap between amino-N content and LAP activity in seminal and lateral root tips, as well as seminal roots, highlighted the intricate interplay between plants and microorganisms in N acquisition. Remarkably, we also uncovered a significant decoupling of LAP activity from amino-N in lateral roots and bulk soil. The distinct patterns in different root parts provided a perspective on the major origins of enzyme production in the rhizosphere. Endogenous LAP production by roots and root-associated microbes in seminal roots and root tips contrasted with the reliance on exogenous rhizosphere microorganisms for enzyme activity in lateral roots. This finding not only advances our understanding of N acquisition but also opens up the new avenues for discussion on the ecological roles of different root segments in shaping the rhizosphere environment.