Soil inorganic carbon (SIC) constitutes a major carbon (C) source on Earth, playing a crucial role in CO2 sequestration and climate regulation. While plant growth and microbial activity primarily influence the soil organic C (SOC) pool through the release of dissolved organic C (DOC), their indirect effects on dissolved inorganic C (DIC), and SIC, require further exploration. This study investigates the impact of plant growth on DIC and SIC dynamics in a carbonate-poor soil planted with either C3 (Silphium perfoliatum L.) or C4 (Zea mays L.) plants. Lysimeter leachates were analysed to assess DIC and DOC concentrations, pH, CO2 efflux, and δ13C isotopes over two weeks under varying drought and irrigation conditions. Findings revealed significantly higher DIC concentrations compared to DOC in leachates of both plant types, alongside increased CO2 efflux and pH, indicative of increased root respiration dynamics. Interestingly, the δ13C values of DOC were nearly uniform across C3 and C4 plots (-29 ± 0.7‰), while DIC values displayed greater variability, ranging from ~-7 to -20‰. A mass balance approach further identified that C4 plant contributions could account for up to ~62% of the DIC pool. These results challenge the traditional viewpoint that plant growth primarily influences the DOC rather than the DIC pool, thus, underscoring the role of root and rhizomicrobial respiration in enhancing DIC contributions and the dynamics of soil inorganic C. These new insights into the complex interactions between plant growth, microbial activity, and soil inorganic carbon, emphasize their importance in climate change mitigation strategies.