Mixed forests have gained increasing attention for afforestation effort on the Chinese Loess Plateau (CLP), while the understanding of how tree water use strategies change across pure and mixed forests is still challenge. In this study, we compared the water use strategies of typical pure Pinus tabuliformis (PT), pure Robinia pseudoacacia (RP) and mixed PT x RP forest in central CLP during a wet year (2022) and a normal year (2023). We examined vertical distribution of fine root dry biomass and length density, monitored soil water content (SWC) and stand transpiration (Tr), applied stable water isotopes to analyse water source utilization and assessed stomatal regulation strategies during the growing seasons. The results indicated that the PT x RP forest exhibited higher fine root dry biomass than both pure forests, while its fine root length density was intermediate, exceeding that of the PT forest but remaining lower than that of the RP forest. Variations in SWC and Tr across growing seasons was greater in PT x RP forest than in PT forest but less than in RP forest. The Tr trends corresponded to fine root length density and showed significant responses to environmental drivers (air temperature, net radiation, vapour pressure deficit (VPD) and reference evapotranspiration). All forests reduced water absorption from surface layer from a wet to a normal year, with the PT x RP forest exhibiting a larger increase in the absorption proportion from the deep layer (7.8% for PT and 6.4% for RP in the PT x RP) compared to both the PT (6.3%) and the RP (6.0%) forests. Analysis of the stomatal conductance's response to VPD showed that stomatal regulation was stricter in the PT x RP forest (m/Gcref: 0.7-1.3) than in the pure forests (0.4-0.9). Overall, mixed forests employed more conservative water use strategies than pure forests, as evidenced by deep water acquisition and stricter stomatal regulation. This study provides critical scientific insights for CLP afforestation and water resource management.Read the free for this article on the Journal blog.