Variable Responses of Plant Water Use to Soil Water Availability in Robinia Pseudoacacia under Prolonged Drought

Large-scale afforestation on the Loess Plateau has been subjected to more frequent and severe drought due to climate change. However, there is a lack of definite evidence elucidating the adjustments in water supply-demand relationships under prolonged drought. In this study, we investigated the responses of plant characteristics related to plant water supply and demand in 2-year-old Robinia pseudoacacia seedlings to soil water availability (SWA). We systemically analyzed the acclimation of plant water use to prolonged drought. A logistic function was used to fit relationships between normalized net photosynthetic rate (P-n), transpiration rate (T-r), stomatal conductance (G(s)), soil-root hydraulic conductance (K-sr), root-leaf hydraulic conductance (K-rl), and whole plant hydraulic conductance (K-plant) with SWA. The results revealed significant difference in responses of these parameters to SWA (p < .001). The sensitivities of P-n, T-r, and G(s) to drought increased from 60-day to 120-day drought, contributing to reduce water consumption. Meanwhile, the relative stable sensitivities of hydraulic conductance (K-sr, K-sr, and K-plant) promoted a consistent water supply at different ecological levels. Additionally, coordination between G(s) with hydraulic conductance helped maintain normal physiological activities under drought. These findings enhance our understanding of adjustments in plant water use in response to prolonged drought in Robinia pseudoacacia.