Differential response of plant transpiration to uptake of rainwater-recharged soil water for dominant tree species in the semiarid Loess Plateau

Abstract

Establishing whether uptake of rainwater-recharged soil water (RRS) can increase plant transpiration in response to rainfall pulses requires an 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, the predawn leaf water potential (ψpd), the midday leaf water potential (ψm), the gradient of leaf water potential (ψpd-ψm), and the 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 ψpd-ψm, RRS uptake proportion (RUP), and the relative response of daily normalized sap flow (SFR) 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 ψpd-ψm was consistent with high SFR for H. rhamnoides and the small ψpd-ψm was consistent with low SFR 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 SFR was significantly affected by RUP and ψpd-ψm for H. rhamnoides and significantly influenced by ψpd-ψm for P. tomentosa (P<0.05). However, the SFR was significantly influenced by RUP and ψpd-ψm for both species in the mixed plantation. These results indicate that mixed afforestation enhanced the influence of RRS uptake on 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.