Long-term land use conversion influence on soil pore structure and organic carbon

Abstract

Pore structure plays a crucial role in soil carbon (C) dynamics, influencing physical, biological, and chemical processes that govern C protection or decomposition, yet its impact on C losses and gains during land use changes is not fully understood. We investigated the pore structure using X-ray computed tomography (CT) and characterized soil organic C (SOC) and its chemistry using a “space-for-time” substitution approach across four land use: an uncut deciduous forest, a never-tilled grassland, an early successional community restoring native vegetation on historically cultivated soil, and a conventionally intensively managed agricultural system. Soil of intensive agriculture displayed lower porosity (10–12 %), lower volume of pores in the 30–150 μm range (10–20 %), and reduced SOC content (42–75 %) as compared to those in undisturbed forest and grassland. While restoration of the early successional plant community led to a substantial recovery of the pore structure, with pore characteristics approaching those of undisturbed land uses, its SOC-related measures, including particulate and mineral associated organic C, and microbial biomass C, constituted only ∼50 % of the undisturbed grassland and forest benchmarks. Analysis of functional group chemistry demonstrated that SOC gained in agricultural soil upon establishment of early successional community differs in its chemical composition from that lost during past agricultural land use. By integrating pore structure measurements via CT, C fractionation, and microbial activity data, this study highlights the intricate interplay between soil structure and C dynamics, exploring the influence of the pore structure on ecosystem C processing and storage capacity.