Mineral reactivity determines root effects on soil organic carbon

• Published in: Nature communications Vol. 14; no. 1; pp. 4962 - 10
• Main Authors: Liang, Guopeng, Stark, John, Waring, Bonnie Grace
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 16.08.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 45/23; 631/158/855; 704/47/4113; Carbon; Carbon cycle; Carbon sequestration; Clay; Cycles; ENVIRONMENTAL SCIENCES; Exudates; Humanities and Social Sciences; microbial ecology; Microorganisms; multidisciplinary; Organic carbon; Organic matter; Respiration; Roots; Science; Science (multidisciplinary); soil carbon; Soil ecology; soil microbes; Soil organic matter; Soils
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-40768-y

Modern conceptual models of soil organic carbon (SOC) cycling focus heavily on the microbe-mineral interactions that regulate C stabilization. However, the formation of ‘stable’ (i.e. slowly cycling) soil organic matter, which consists mainly of microbial residues associated with mineral surfaces, is inextricably linked to C loss through microbial respiration. Therefore, what is the net impact of microbial metabolism on the total quantity of C held in the soil? To address this question, we constructed artificial root-soil systems to identify controls on C cycling across the plant-microbe-mineral continuum, simultaneously quantifying the formation of mineral-associated C and SOC losses to respiration. Here we show that root exudates and minerals interacted to regulate these processes: while roots stimulated respiratory C losses and depleted mineral-associated C pools in low-activity clays, root exudates triggered formation of stable C in high-activity clays. Moreover, we observed a positive correlation between the formation of mineral-associated C and respiration. This suggests that the growth of slow-cycling C pools comes at the expense of C loss from the system. Root exudates can either promote or impede the formation of stable, mineral-associated soil organic carbon (MAOC). Yet, carbon stabilisation in MAOC is decoupled from changes in the total soil carbon pool, i.e., carbon sequestration.