Differential response of plant transpiration to uptakeof rainwater-recharged soil water for dominanttree species in the semiarid Loess Plateau

Whether uptake of rainwater-recharged soil water (RRS) can increase plant transpiration in response to rainfall pulses requires investigation to evaluate plant adaptability, especially in water limited regions where rainwater is the only replenishable soil water source. In this study, the water sources from RRS and three soil layers, predawn (Ψ_pd), midday (Ψ_m) and gradient (Ψ_pd−Ψ_m) of leaf water potential, and plant transpiration in response to rainfall pulses were analyzed for two dominant tree species, Hippophae rhamnoides subsp. sinensis and Populus tomentosa, in pure and mixed plantations during the growing period (June–September). Mixed afforestation significantly enhanced Ψ_pd − Ψ_m, RRS uptake proportion (RUP), relative response of daily normalized sap flow (SF_R), and reduced the water source proportion from the deep soil layer (100–200 cm) for both species (P < 0.05). In pure and mixed plantations, the large Ψ_pd − Ψ_m was consistent with high SF_R for H. rhamnoides, and the small Ψ_pd − Ψ_m was consistent with low SF_R for P. tomentosa, in response to rainfall pulses. Therefore, H. rhamnoides and P. tomentosa exhibited anisohydric and isohydric behavior, respectively, and the former plant species was more sensitive to rainfall pulses than P. tomentosa. Furthermore, in pure plantations, the SF_R was significantly affected by RUP and Ψ_pd − Ψ_m for H. rhamnoides, and was significantly influenced by Ψ_pd − Ψ_m for P. tomentosa (P < 0.05). However, the SF_R was significantly influenced by RUP and Ψ_pd − Ψ_mfor both species in the mixed plantation. These results indicate that mixed afforestation enhanced the influence of RRS uptake to plant transpiration for these different rainfall pulse sensitive plants. This study provides insights into suitable plantation species selection and management considering the link between RRS uptake and plant transpiration in water limited regions.