Calcium-Enriched Irrigation Drives Plant-Mediated Carbon Sequestration Dynamics in Karst Soils

Abstract

Mineral-organic complexes are key regulators of soil organic carbon (SOC) sequestration in agricultural ecosystems. As a dominant soil mineral, calcium (Ca) plays a particularly important role in SOC stabilization. Although numerous studies have indicated that Ca can enhance SOC storage, particularly in the karst regions of Southwest China, the specific mechanisms underlying Ca-SOC interactions and their associated biological processes remain poorly understood. In this study, we used a controlled pot experiment with maize (Zea mays L.) irrigated for 112 days with allogenic waters containing different Ca²⁺ concentrations (2, 54, and 108 mg L^-1). Soil respiration, in situ soil CO₂ concentrations, and leachate carbon fractions were monitored at 7-day intervals, and leachate carbon fractions including total organic carbon (TOC), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC). The results showed that: (1) soil respiration rates and CO₂ concentrations were progressively higher in maize rhizosphere soils than in unvegetated controls and displayed pronounced temporal dynamics; (2) TOC, DOC, and DIC concentrations in leachates were significantly elevated in vegetated systems compared with bare soils, indicating enhanced carbon mobilization and transformation driven by plant activity; (3) DIC sources differed between treatments, with carbonate-derived carbon being the predominant contributor to DIC in maize-cultivated soils, while soil/atmospheric CO₂ was the main source in bare soils. These findings highlight that Ca-rich irrigation, in com­bination with plant and microbial activity, can substantially modify C fluxes and carbonate weathering pathways in calcare­ous soils, providing mechanistic insights into biologically medi­ated carbon sequestration processes in Southwest China’s karst agroecosystems.