Root resource acquisition strategies mediate rhizosphere microbiome responses and network complexity under long-term nitrogen addition

Background and Aims Long-term nitrogen (N) deposition profoundly influences belowground ecological processes in forests. However, it remains unclear whether plant fine-root resource acquisition strategies regulate rhizosphere microbial community responses to N addition. Methods Based on a 22-year N addition experiment, this study investigated two tree species with contrasting strategies: Larix gmelinii (larch), exhibiting a conservative "low-investment, slow-return" strategy, and Fraxinus mandshurica (ash), which adopts an acquisitive "high-investment, fast-return" strategy. We explored how fine-root resource acquisition strategies regulate rhizosphere microbial community composition, metabolic limitations, and co-occurrence networks. Results Our results showed that N addition significantly strengthened the acquisitive strategy in ash but did not alter the resource acquisition strategy of larch fine roots. In ash, this enhanced acquisitive strategy drove the enrichment of specific bacterial taxa (Acidobacteriota and Proteobacteria) and fungal taxa (Ascomycota) in the rhizosphere following N addition, whereas the microbial composition in the larch rhizosphere remained largely unchanged. Furthermore, mediated by the root resource acquisition strategy, N addition alleviated microbial carbon limitation in the ash rhizosphere and fostered more complex and stable bacterial networks. In contrast, N addition intensified microbial carbon limitation in the larch rhizosphere, simplifying its bacterial network. Conclusion This study demonstrates that plant fine-root resource acquisition strategy is a key trait governing rhizosphere microbial response to N addition. N addition disproportionately benefits the rhizosphere ecosystems of species with inherently acquisitive root strategies by enhancing their ecological stability.