Soil carbon and nitrogen contents in forest soils are related to soil texture in interaction with pH and metal cations

Summary

This large-scale observational study across Swedish forest soils demonstrates that soil carbon concentration is strongly negatively related to pH, with very acidic soils (pH ≤ 4.0) containing 2.6 times more carbon than neutral soils in the top mineral layer. By contrast, nitrogen concentration varies less with pH but is substantially influenced by soil texture, with clay and fine silt soils containing 2.3 times more nitrogen than sandy soils. The findings highlight distinct mechanisms controlling carbon and nitrogen storage: pH effects on microbial respiration dominate carbon dynamics, whilst the high charge density of organic nitrogen makes texture a stronger predictor of nitrogen retention.

UK applicability

UK soils, particularly acidic upland and podzolic soils, would likely exhibit the carbon accumulation patterns described for very acidic forest soils. However, the findings derive from boreal and temperate Swedish forests; temperate UK woodlands and agricultural systems may show different relationships depending on management history, vegetation type, and local pH buffering capacity.

Key measures

Organic carbon concentration, nitrogen concentration, C:N ratio, soil pH, exchangeable aluminium, exchangeable calcium, soil texture (clay, silt, sand content) measured in organic layer and three mineral soil depth increments

Outcomes reported

The study quantified relationships between soil carbon and nitrogen concentrations and soil texture, pH, and exchangeable metal cations across 1992 temperate and boreal forest soils at multiple depths (0–65 cm). It examined how pH and soil texture interact to influence carbon and nitrogen storage patterns in forest ecosystems.

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