Soil parent material controls organic matter stocks and retention patterns in subtropical China

Purpose The influence of parent material on soil organic carbon (SOC) retention remains largely unstudied. Here, we aimed to reveal the role of soil parent material on SOC stocks and elucidate the underlying SOC retention patterns for soils derived from limestone, quaternary red earth, granite, basalt, and tertiary red sandstone in subtropical China. Materials and methods The study assessed 110 topsoils (0–20 cm) under two land uses (forest and cultivated), but with similar topography. We compared soil properties (pH, oxides, multivalent cations, texture, aggregates) and SOC stocks, total SOC concentration as well as three organic C fractions (active, slow, and passive C). Factors influencing SOC concentration were explored using a combination of stepwise multiple regression analysis and redundancy analysis. Results and discussion Topsoil SOC stocks and SOC concentration varied significantly among the five parent materials, with the greatest values all observed in limestone-derived soils and the lowest in tertiary red sandstone–derived soils. While parent material significantly influenced both quantity and quality of SOC, there was no land use effect on the proportion of organic C fractions. Our results have also shown that parent material mediates land use impacts on SOC. The SOC stocks and SOC concentration in limestone, quaternary red earth, and basalt-derived soils were significantly higher in forest than in arable soils, while no significant land use effect was found for soils derived on granite and tertiary red sandstone. Soil aggregates, texture, content of Fe oxides, and multivalent cations accounted for 67.8% of the variation in SOC concentration, and both SOC stocks and SOC concentration were more closely related to aggregation and soil texture. The major influencing factors for SOC retention differed with parent material, with Ca 2+ /Mg 2+ -mediated interactions between organic matter and mineral surfaces being the main regulating processes for limestone-derived soils and oxide-mediated mechanisms to form stable aggregates being the likely SOC protecting patters for quaternary red earth and basalt-derived soils. Due to the coarse texture and low aggregate stability, the soils derived from granite and tertiary red sandstone lacked the properties for SOC preservation, with pH the main predictor for SOC concentration. Macroaggregates (> 2 mm) played especially important role in shaping SOC stocks. Conclusions Parent material exerts an influence on