Mapping global soil acidification under N deposition

Soil pH is critically important in regulating soil nutrients and thus influencing the biodiversity and ecosystem functions of terrestrial ecosystems. Despite the ongoing threat of nitrogen (N) pollution especially in the fast-developing regions, it remains unclear how increasing N deposition affects soil pH across global terrestrial ecosystems. By conducting a global meta-analysis with paired observations of soil pH under N addition and control from 634 studies spanning major types of terrestrial ecosystems, we show that soil acidification increases rapidly with N addition amount and is most severe in neutral-pH soils. Grassland soil pH decreases most strongly under high N addition while wetlands are the least acidified. By extrapolating these relationships to global mapping, we reveal that atmospheric N deposition leads to a global average soil pH decline of -0.16 in the past 40 years and regions encompassing Eastern United States, Southern Brazil, Europe, and South and East Asia are the hotspots of soil acidification under N deposition. Our results highlight that anthropogenically amplified atmospheric N deposition has profoundly altered global soil pH and chemistry. They suggest that atmospheric N deposition is a major threat to global terrestrial biodiversity and ecosystem functions.

Automated summary

Soil pH plays a critical role in regulating soil nutrients and impacting biodiversity and ecosystem functions in terrestrial ecosystems. This study conducted a global meta-analysis and found that soil acidification increases with nitrogen (N) deposition, particularly in neutral-pH soils. Grassland soils are most strongly affected by high N addition, while wetland soils are least acidified. The study also revealed that atmospheric N deposition has led to a global average soil pH decline of -0.16 in the past 40 years, with certain regions being hotspots of soil acidification. These findings emphasize the significant threat that anthropogenic N deposition poses to global terrestrial biodiversity and ecosystem functions.