Differential response of plant water consumption to rainwater uptake for dominant tree species in the semiarid Loess Plateau

Abstract. Whether uptake of rainwater can increase plant water consumption in response to rainfall pulses requires investigation to evaluate the plant adaptability, especially in water limited regions where rainwater is the only replenishable soil water source. In this study, the water sources from rainwater and three soil layers, predawn (Ψ_pd), midday (Ψ_m) and gradient (Ψ_pd−Ψ_m) of leaf water potential, and water consumption in response to rainfall pulses were analyzed for two dominant tree species, Hippophae rhamnoides and Populus davidiana, in pure and mixed plantations during the growing period (June–September). In pure plantations, the relative response of daily normalized sap flow (SF_R) was significantly affected by rainwater uptake proportion (RUP) and Ψ_pd−Ψ_m for H. rhamnoides, and was only significantly influenced by Ψ_pd−Ψ_m for P. davidiana (P < 0.05). Meanwhile, 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 the low SF_R for P. davidiana, in response to rainfall pulses. Therefore, H. rhamnoides and P. davidiana exhibited sensitive and insensitive responses to rainfall pulses, respectively. Furthermore, mixed afforestation significantly enhanced RUP, SF_R, and reduced the water source proportion from the deep soil layer (100–200 cm) for both species (P < 0.05). The SF_R was significantly influenced by RUP and Ψ_pd−Ψ_m for both species in the mixed plantation. Lower Ψ_m and higher Ψ_pd were adopted by H. rhamnoides and P. davidiana in mixed plantation, respectively, to enlarge Ψ_pd−Ψ_m, enhance rainwater uptake, and decrease water source competition from the deep soil layer. These results indicate that mixed afforestation enhanced the influence of rainwater uptake to water consumption after rainfall pulse, regardless of sensitivity to rainfall pulses. This study provides insights into suitable plantation species selection and management considering the link between rainwater uptake and consumption in water limited regions.