The Effect of Soil Enzymes and Polysaccharides Secreted by the Roots of Salvia miltiorrhiza Bunge under Drought, High Temperature, and Nitrogen and Phosphorus Deficits

Root exudates serve as crucial mediators for information exchange between plants and soil, and are an important evolutionary mechanism for plants' adaptation to environmental changes. In this study, 15 different abiotic stress models were established using various stress factors, including drought (D), high temperature (T), nitrogen defi- ciency (N), phosphorus deficiency (P), and their combinations. We investigated their effects on the seedling growth of Salvia miltiorrhiza Bunge and the activities of Solid-Urease (S-UE), Solid-Nitrite Reductase (S-NiR), Solid-Nitrate Reductase (S-NR), Solid-Phosphotransferase (S-PT), and Solid-Catalase (S-CAT), as well as the contents of polysaccharides in the culture medium. The results showed that the growth of S. miltiorrhiza was inhibited under 15 stress conditions. Among them, 13 stress conditions increased the root-shoot ratio. These 15 stress conditions significantly reduced the activity of S-NR, two combinations significantly improved the activity of S-NIR, they were synergistic stresses of high temperature and nitrogen deficiency (TN), and synergistic stresses of drought and nitrogen deficiency (DN) (p < 0.05). The activity of S-UE was significantly improved under N, D, T, synergistic stresses of drought and high temperature (DT), DN, synergistic stresses of drought and phosphorus deficiency (DP), and synergistic stresses of high temperature, nitrogen, and phosphorus deficiency (TNP) stress conditions (p < 0.05). Most stress combinations reduced the activity of S-PT, but D and T significantly improved it. (p < 0.05). The N, DN, and TN stress conditions significantly reduced S-CAT activity. The P, DT, and synergistic stresses of drought, high temperature, and phosphorus deficiency (DTP) significantly decreased the total polysaccharide content of the soil (p < 0.05). The research suggested that abiotic stress hindered the growth of S. miltiorrhiza and altered the behavior of root secretion. Roots regulated the secretion of several substances in response to various abiotic stresses, including soil nitrogen cycle enzymes, phosphorus transport-related enzymes, and antioxidant enzymes. In conclusion, plants regulate the utilization of rhizosphere substances in response to abiotic stresses by modulating the exudation of soil enzymes and polysaccharides by the root system. At the same time, soil carbon sequestration was affected by the adverse environment, which restricted the input of organic matter into the soil.