Plant Legacy Effects Shape Rhizosphere Microbial Diversity, Function, and Organic Nitrogen Dynamics

The organic form of nitrogen (N) is a critical intermediate shaping mutualistic and competitive interactions between plant roots and soil microorganisms in the rhizosphere. Yet, the spatial dynamics of nutrient cycling and microbial community assembly in legacy-affected soils remain poorly understood. In this study, we used visualization approaches to localize hotspots of organic N and associated enzymatic activity in soils influenced by plant legacy effects, and we analyzed the microbial communities associated with these hotspots. Our results showed that plant N content and rhizosphere organic N declined after one generation of plant growth. These reductions were accompanied by increased soil microbial diversity and a community shift from copiotrophic to oligotrophic dominance. The abundance of beneficial microorganisms was higher in the newly-growth roots, while soil-borne plant pathogen increased in the legacy-affect soil. Furthermore, genes abundance of N-related transporter and urease were detected exclusively in the rhizosphere of developed seminal roots in the legacy-affect soil, highlighting functional specialization in response to plant-driven soil modifications. These findings suggest that plant legacy effects can restructure rhizosphere nutrient distribution and microbial communities in ways that influence nutrient availability, root health, and plant-soil feedbacks. Understanding these spatially explicit interactions can improve predictions of plant resilience under nutrient-limited conditions and guide strategies to harness beneficial microorganisms for sustainable nutrient management.