A conceptual model hypothesizing processes contributed to the nonlinear responses of belowground C processes to changes in precipitation at different scales from organs to ecosystems. Root:shoot ratio, root turnover time, species composition are three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect response pattern of belowground C processes to changing precipitation.