Concurrent alien plant invasion and biodiversity loss enhance soil microbial carbon use efficiency by shifting the balance between microbial carbon and nitrogen acquisition

The proliferation of invasive alien plants (IAPs), coupled with the decline in native biodiversity, poses a significant threat to global ecological stability. These processes disrupt native plant communities and trigger cascading effects on vital soil functions, such as carbon cycling. While IAPs are known to alter soil properties, the mechanisms driving these changes, particularly in the context of simultaneous biodiversity loss, remain poorly understood. This pot-based study simulated the reduction in native plant biodiversity caused by Solidago canadensis L. invasion, a highly aggressive IAP, to explore its impact on soil microbial resource acquisition strategies and carbon use efficiency (CUE). Four treatments were established: early invasion with high native plant diversity, moderate invasion with moderate diversity, high invasion with low diversity, and complete invasion with no native diversity. The soil microbial nutrient acquisition strategies and CUE were analyzed using eco-enzymatic stoichiometry within the frameworks of ecological stoichiometry and metabolic ecology theories. Our results revealed a significant depletion of inorganic nitrogen and dissolved organic nitrogen in high invasion with low diversity treatment soils (p < 0.05), leading to nitrogen limitation. Microbial nutrient acquisition strategies shifted toward nitrogen prioritization with increasing S. canadensis invasion, reflected by reduced eco-enzymatic carbon-to-nitrogen stoichiometry. CUE increased significantly along the S. canadensis invasion gradient, rising by 55.7%–63.5% (p < 0.05), driven by shifts in microbial nutrient acquisition strategies. These findings demonstrate that S. canadensis invasion-induced biodiversity loss disrupts nutrient dynamics and enhances CUE, potentially accelerating soil fertility degradation and ecosystem instability.