Abstract
Understanding soil biogeochemical responses to increased nitrogen (N) deposition is essential for assessing and mitigating the impacts of global environmental change on terrestrial ecosystems. However, the effects of N addition on key soil elements—those critical for ecosystem productivity and pollution dynamics—remain insufficiently understood, particularly in vulnerable Mediterranean ecosystems characterized by phosphorus (P) and/or water limitations. Therefore, we examined the effects of simulated N deposition on extractable total P (ETP) and its organic and inorganic fractions, alongside the extractable concentrations of 12 mineral elements in a P-limited Mediterranean shrubland. Over the study period, N addition notably increased ETP and its fractions, while decreasing iron (Fe) concentrations. The increase in extractable P is likely attributable to enhanced activity of P-mobilizing enzymes, coupled with a decline in plant photosynthetic activity and nutrient uptake capacity during colder seasons. The reduction in extractable Fe may be linked to lower activity of carbon (C)- and N-mobilizing enzymes under N addition. Our findings suggest that N accumulation initially triggers ecosystem mobilization of less available nutrients, potentially alleviating existing P limitations. However, the observed shifts in enzyme activity—from N or C to P mobilization—indicate that the ecosystem's capacity to mobilize P may become saturated under prolonged N deposition, ultimately intensifying P limitation and favoring P-efficient and acid-tolerant species over time.