Effects of Understory Intercropping With Salt‐Tolerant Legumes on Microbial Resource Limitation in Coastal Saline‐Alkali Land

The accumulation of salts in coastal saline‐alkali soils significantly impairs their ecological functions and productivity. As a sustainable amelioration strategy, forest–legume intercropping systems have attracted considerable attention; however, the regulatory mechanisms underlying their effects on microbial metabolic limitations remain insufficiently understood. This study, based on a field experiment, integrated high‐throughput sequencing with enzymatic stoichiometry approaches to determine whether the intercropping system could alleviate microbial energy and nutrient limitations and to elucidate the underlying pathways. The results showed that although the short‐term forest–legume system alleviated microbial nitrogen limitation, it did not fundamentally alter the original nitrogen‐limited status; meanwhile, carbon limitation was further intensified. Understory intercropping enhanced soil microbial richness and diversity indices and altered community composition, with increased relative abundances of Proteobacteria and Bacteroidota. Several dominant phyla (e.g., Acidobacteriota, Glomeromycota, Basidiomycota) were closely related to microbial resource limitations. At the T. hybrid ‘Zhongshanshan’ experimental site, the fungal Shannon index exhibited the strongest total effect on soil carbon, nitrogen, and phosphorus limitations (0.715, 0.536, and 0.581, respectively). At the C. illinoensis site, the fungal Chao1 index had the most pronounced effect on carbon limitation (0.482), while the bacterial Chao1 index showed strong explanatory power for nitrogen and phosphorus limitations (−0.840 and 0.518, respectively). These findings highlight the potential of short‐term understory intercropping of green manure in mitigating microbial nutrient limitations, providing valuable insights for optimizing coastal saline‐alkali soil utilization.