Effects of Water Stress on Drought Resistance Physiological Characteristics of Pinus tabulaeformis

[Objective] Exploring the drought resistance characteristics of Pinus tabulaeformis, a major afforestation tree species for soil and water conservation, under different water stress to provide a scientific basis for the management of P. tabulaeformis artificial forests in the region. [Methods] Using one-year P. tabulaeformis seedings as the research subject, four levels of water stress treatments were set up, which were control group (CK), mild stress (RE25%), moderate stress (RE50%) and severe stress (RE75%), respectively, the growth characteristics, hydraulic function and osmotic regulatory substance content of P. tabulaeformis seedlings were analyzed after different water stress treatments, and their correlation was analyzed. [Results] (1) Compared with the CK treatment, after twenty months of RE50% and RE75% treatment, the aboveground biomass of P. tabulaeformis significantly decreased by 19.1% and 37.0%, respectively, while the underground biomass significantly increased by 13.7% and 23.9%, respectively. (2) In the CK, RE25%, RE50% and RE75% treatments, the water potential threshold for embolism resistance of P. tabulaeformis new branches was -1.43, -2.04, -0.91 and -0.58 MPa, respectively. (3) Compared with CK, in the RE50% and RE75% treatments, the soluble sugar content in the coarse roots significantly increased by 123.3% and 121.9%, respectively, the starch content significantly increased by 15.0% and 58.0%, respectively, and the total nonstructural carbohydrate (NSC) content significantly increased by 104.0% and 83.2%, respectively. In the RE75% treatment, the proline content in the new branches significantly decreased by 43.0%, while the K+ content decreased by 23.7% compared with the CK group. (4) The contribution rates of various osmotic regulating substances in various organs to hydraulic function under different water stress were as follows: NSC, starch, soluble sugars, K+, proline and soluble sugars in tracheid sap. [Conclusion] Mild water stress could enhance the embolism resistance of new branches. P. tabulaeformis seedlings maintained their metabolism by increasing root carbon storage. Meanwhile, the numerous organs of P. tabulaeformis improved cell concentration, reduced osmotic potential, and preserved hydraulic function to adapt to water stress environment by coordinating the accumulation of osmotic regulating substances. This study advanced the understanding of P. tabulaeformis' drought resistance mechanism and provided a scientific basic for the management of P. tabulaeformis artificial forests on the Loess Plateau.