Seasonal variations of plant water use in the karst desertification control

Understanding the water use characteristics of plants is crucial for the sustainability of forest water management and vegetation restoration. The vegetation restoration program in the karst desertification areas of southwest China has been implemented for more than two decades, and remarkable achievements have been made in ecological restoration. However, the water use characteristics of revegetation are still poorly understood. We investigated the water uptake patterns and water use efficiency of four woody plants (Juglans regia, Zanthoxylum bungeanum, Eriobotrya japonica, and Lonicera japonica) using stable isotopes (δ²H, δ¹⁸O, and δ¹³C) in combination with the MixSIAR model. The results showed that plants responded to seasonal changes in soil moisture with flexible water uptake patterns. Differences in water use sources among the four plant species during the growing season indicated the occurrence of hydrological niche separation, which is the key to vegetation symbiosis. Throughout the study period, groundwater made the lowest contribution to plants (9.39 %~16.25 %), and fissure soil water made the highest contribution (39.74 %~64.71 %). Among them, shrubs and vines were more dependent on fissure soil water compared to trees (50.52 %~64.71 %). Furthermore, plant foliar δ¹³C was higher in the dry season than in the rainy season. Evergreen shrubs (-27.94 ‰) exhibited higher water use efficiency compared to other tree species (-30.48 ‰~-29.04 ‰). The water use efficiency of four plants showed seasonal variation and was influenced by the water availability caused by soil moisture. Our study demonstrates that fissure soil water is an important water source for karst desertification revegetation and that seasonal changes in water use characteristics are influenced by species-level water uptake patterns and water use strategies. This study provides a reference for vegetation restoration and water resource management in karst areas.