Meta‐Analysis of Nitrogen Effects on Soil Phosphorus Pools: The Central Role of Soil pH

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ABSTRACT Increasing nitrogen (N) deposition and intensive fertilisation practices have a complex impact on soil phosphorus (P) dynamics and P bioavailability, with significant consequences for ecosystem productivity. However, it remains unclear how N inputs affect soil P pools and to what extent these effects depend on ecosystem type and initial soil pH. To address these knowledge gaps, we conducted a meta‐analysis based on 70 N addition studies (published from 1990 to 2023) and 1989 observations across cropland, grassland and forest ecosystems; the meta‐analysis incorporated 30 variables related to soil P pools. Our results reveal that initial soil pH serves as the dominant regulator of soil P responses to N enrichment. In circumneutral/alkaline soils (pH > 5.5), N addition significantly reduced labile inorganic P (Pi) by 12.4%, likely due to the dissolution of Ca 2+ ‐bound P. This, together with observed. Increases in resin‐P, may support enhanced plant higher P demands under N addition. Conversely, in acidic soils, N addition significantly reduced resin‐P by 12.7%, labile organic P (P o ) by 12.8% and moderately labile P o by 6.7%. Additionally, N addition increased labile P i by 12.0%, moderately labile P i by 8.3% and residual P by 4.7%, respectively. These soil P pool dynamics in acidic soils were associated with enhanced phosphatase activity and greater P o mineralization, as well as increased adsorption/coprecipitation with Fe/Al‐(hydr)oxides, as suggested by the negative relationship between resin‐P and exchangeable Fe 3+ /Al 3+ under N addition. In conclusion, the initial soil pH may be a critical determinant of the direction and magnitude of N addition effects on P bioavailability. Understanding this pH‐dependent framework is essential for optimising P management in agroecosystems and sustaining ecosystem productivity in the context of global N enrichment.

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