Epikarst shallow fissure soil systems are key to eliminating karst drought limitations in the karst rocky desertification area of SW China

Abstract Surface soil water shortages are among the primary factors limiting revegetation in most degraded regions with shallow soil, especially in karst areas. Finding water sources for plants is an urgent task to ensure maximum vegetation restoration in these areas. We combined soil water content monitoring and isotope tracing to reveal the principal water source supply systems for plants in karst areas. The results showed that the content and storage of water in the shallow fissure soil system (SFSS) of the epikarst zone were consistently higher and more temporally stable than that of the surface soil. Thus, epikarsts with dissolution voids and fissures are important, stable aquifers that provide water to plants. Moreover, the IsoSource results showed that the SFSS was the primary water source for three monitored tree species ( Cupressus torulosa D. Don, Pyracantha fortuneana [Maxim.] Li and Rosa cymosa Tratt.), especially C. torulosa and P. fortuneana . The water‐uptake patterns of C. torulosa and P. fortuneana changed from dominant SFSS and surface soil water sources during the rainy period to the dominant SFSS and transfer zone (TZ) of vadose zone water sources during the dry period. In contrast, Rhynchospora cymosa uses water from SFSS and TZ water sources only during drought. These results suggest that the SFSS is key to eliminating vegetation restoration limitations due to surface drought in karst areas. It is proposed that deeply rooted plants with dimorphic root systems are optimal for sustainable vegetation restoration in karst areas.