Soils control biogeochemical shifts resulting from the conversion of native forest to pine plantations

Conversion from native temperate deciduous Nothofagus spp. forests to exotic Pinus spp. plantations in South-Central Chile, can substantially alter soil carbon (C) and nutrient cycling. We assessed the biogeochemical shifts resulting from this forest conversion by monitoring carbon and nutrient dynamics at 10 paired adult native forest and plantation sites across contrasting soil types (5 sites), including litterfall, LAI, fine root biomass, and soil CO₂ efflux, over a period of three years. In addition, we quantified aboveground tree biomass and total C, N, and P stocks in trees and soils. C inputs were significantly higher in native systems than in plantations (5.17 ± 1.19 vs. 3.19 ± 0.99 Mg C ha⁻¹ year⁻¹, respectively). Native forests also exhibited higher total C losses through soil CO₂ efflux (-3.19 ± 1.68 Mg C ha⁻¹ year⁻¹) than pine plantations (-2.54 ± 1.52 Mg C ha⁻¹ year⁻¹), yet maintained a more favorable balance between inputs and losses, largely due to differences in the dominant C input pathways. Native forests showed greater fine-root production and deeper, denser rooting systems, whereas plantations were characterized by higher litterfall and faster decomposition rates, potentially accelerating carbon mineralization. Across soil types, native forests exhibited significantly higher aboveground biomass than adjacent plantations. Although aboveground carbon stocks tended to be higher in native forests, these differences were not statistically significant when all soil types were considered together. Nevertheless, native forests consistently allocated a greater proportion of carbon belowground, whereas plantations concentrated carbon inputs in aboveground compartments. Native forests also maintained larger soil and aboveground biomass N and P stocks than plantations. Responses varied systematically among soil types, with residual crystalline soils and older volcanic deposits showing higher carbon losses relative to inputs than younger volcanic ash-derived soils. Overall, our results demonstrate that soil parent material modulates post-conversion carbon fluxes and the distribution of ecosystem C, N, and P stocks, highlighting the importance of soil–vegetation interactions when evaluating carbon benefits and long-term sustainability of forest management strategies. • Plantations showed faster litter decomposition and carbon turnover than natural forests. • Fine-root production was consistently higher in native forests. • Soil parent material constrained the balance between carbon inputs and losses. • Soil type modulated post-conversion carbon fluxes and nutrient stocks.