Species-Specific and Altitude-Induced Variation in Karst Plants’ Use of Soil Dissolved Inorganic Carbon

Abstract

Root-derived carbon sources supporting photosynthesis have been demonstrated to contribute to plant carbon gain in many laboratory experiments. However, it remains largely unknown whether and to what extent soil dissolved inorganic carbon (DIC) influences leaf photosynthesis in karst habitats characterized by alkaline soils with low water content. We explored this relationship by measuring the concentrations and carbon isotope signals (δ13C) of soil DIC, as well as the δ13C of water-soluble organic matter (δWSOM) in leaves of nine woody species across an altitudinal gradient in karst habitats. The δWSOM varied among species by 7.23‰ and deviated from the δ13C of photosynthates solely assimilated from atmospheric CO2 (δA) by 0.44–5.26‰, with a mean value of 2.20‰. This systematical discrepancy (δA − δWSOM) could only be explained by the contribution of soil DIC to leaf total photosynthesis (fDIC_soil). The average values of fDIC_soil considerably varied among the nine species, ranging from 2.48% to 9.99%, and were comparable with or slightly lower than those of previous laboratory experiments. Furthermore, the fDIC_soil of two species significantly increased with altitude, whereas another species exhibited an opposite pattern, suggesting a highly spatial heterogeneity of DIC utilization. The present study improved our understanding of how plants adapt to the alkaline–drought soil conditions of karst habitats and thus acquire additional carbon for growth.