Short-term influences of C4 versus C3 plant growth on dissolved inorganic carbon in a carbonate-poor soil

Abstract Background and aims Soil inorganic carbon (SIC) and its dissolved fraction are recognised as dynamic components of the terrestrial carbon (C) cycle. While they contribute to CO 2 dynamics and climate regulation, their short-term responses to plant-driven processes remain poorly understood. This study investigates how growth of a C₃ species ( Silphium perfoliatum L.) and a C₄ species ( Zea mays L.) affects dissolved inorganic and organic C (DIC/DOC) dynamics in a carbonate-poor soil under varying soil moisture conditions. Methods Leachates taken from a two-week lysimeter experiment were analysed for DIC and DOC concentrations, their isotope ratios (expressed as δ 13 C isotope), pH, and the data obtained were complemented with in situ CO 2 efflux measurements. A two-endmember isotope mixing model was used to evaluate contributions of plant-derived C to the DIC pool. Results DIC concentrations exceeded DOC across all treatments. Increased CO₂ efflux and higher pH values indicated enhanced soil respiration. δ 13 C DIC values ranged from –7‰ to –20‰, while δ 13 C DOC remained nearly uniform at –29 ± 0.7‰. Isotope mixing considerations suggested that up to 62% of DIC could be derived from C₄ plant sources. Conclusion Root and rhizomicrobial respiration may measurably influence short-term DIC dynamics in carbonate-poor soils. These findings suggest that DIC fluxes could play a more prominent role in soil C cycling than currently assumed, particularly over short temporal scales.