A Critical Review of Carbon and Phosphorus Linkages in Soils

The stability of soil organic carbon (SOC) is critical for climate change mitigation and underpins key ecosystem services by regulating soil health, nutrient dynamics, and ecosystem resilience. While climate and nitrogen are well-known factors of SOC content and composition, soil total phosphorus (STP) is positively correlated with SOC and exerts a strong but underrepresented control on its persistence. However, the mutuality and mechanisms of the SOC-STP linkage remain insufficiently resolved, limiting its integration into predictive ecosystem C models. This review synthesizes global observational datasets and experimental evidence to evaluate the bidirectional linkage between SOC and STP (and STP pools). Predictive models indicate that SOC and STP are strong mutual predictors globally, reflecting shared controls and feedback due to coupled SOC-organic P cycling. This coupling reflects constrained C:P stoichiometry, declining from 300:1-1300:1 in plant litter to 50:1-300:1 in soil organic matter. These patterns are regulated by plant and microbial P acquisition and utilization strategies, whose quantitative effects remain incompletely constrained. In contrast, predictive models indicate that the SOC-inorganic P (Pi) pools associations are weaker and dynamic. While co-stabilization by metal-bridging regulates the positive SOC-Pi correlation, competitive sorption can reduce Pi retention by 20%-60% and mobilize SOC by 20%-80%. Although these SOC-Pi interactions may exert important local or short-term influences on SOC dynamics, their quantitative ecosystem-level controls remain insufficiently constrained, making them a key but uncertain component of the SOC-STP linkage. Current models simulating SOC-STP linkages remain limited by incomplete/oversimplified representations of plant-microbe-soil mineral feedbacks, challenges in partitioning P between multiple biotic and abiotic sinks, and scarce long-term observations. We propose a dual-pathway framework combining coordinated long-term field studies in understudied ecosystems with next-generation process-based models that explicitly integrate stoichiometric constraints alongside geochemical feedbacks. These advances are essential to improve SOC projections and inform sustainable P management and climate change mitigation strategies.