This book summarizes the physiological effects of bicarbonate in plants and systematically introduces readers to a bidirectional isotope labeling tracer technique used to quantify the contribution of root-derived bicarbonate to total photosynthetic inorganic carbon assimilation in plants. This method helps to shed light on the role of dissolved inorganic carbon from the soil in overall photosynthesis, an aspect that has been underestimated or neglected entirely in the past. The book quantifies the capacity for root-derived bicarbonate assimilation in certain plant species and illustrates the coupling relationship between karstification and photosynthesis. Further, it demonstrates that root-derived bicarbonate utilization is as important as stomatal-derived inorganic carbon assimilation in biological evolution and plant adaptation to the environment. Using numerous models, it also illustrates carbon isotopic mixtures in complex inorganic carbon utilization and supplements the results with numerical calculations presented as tables and figures. In short, the book offers a strikingly new perspective on photosynthesis.