Abstract
Root exudates serve as crucial mediators for the information exchange between plants and soil, which is an important evolutionary mechanism for plants to adapt to environmental changes. In this study, 15 different abiotic stress models were established using various stress factors, including drought (D), high-temperature (T), nitrogen deficiency (N), and phosphorus deficiency (P) and their combinations. We investigated their effects on the seedling growth of Salvia miltiorrhiza Bunge and the activities of urease (S-UE), nitrite reductase (S-NiR), nitrate reductase (S-NR), phosphotransferase (S-PT), and 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 which 13 stress conditions could increase the root-shoot ratio. These 15 stress conditions significantly down-regulated the activity of S-NR, synergistic stresses of drought and nitrogen deficiency (DN) and synergistic stresses of high-temperature and nitrogen deficiency (TN) significantly up-regulated the activity of S-NIR (p <0.05). The 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 deficiency, and phosphorus deficiency (TNP) stresses conditions significantly increased the activity of S-UE (p <0.05). The activity of soil enzyme S-PT could be down-regulated under most stress conditions, but only D and T stresses could significantly up-regulate S-PT activity (p <0.05). The N, DN, and TN stresses conditions significantly reduced S-CAT activity. The content of total polysaccharides in soil was decreased under most stress conditions, and P, DT, and synergistic stresses of drought, high-temperature, and phosphorus deficiency (DTP) stresses were significantly decreased (p <0.05). These results indicated that abiotic stress inhibited the growth of S. miltiorrhiza and altered the root secretion behavior. Plants respond to different abiotic stresses by regulating root secretions, including enzymes of the soil nitrogen cycle, phosphorus transport-related enzymes, and antioxidant enzymes. In conclusion, plants regulate the utilization of rhizosphere substances by regulating the intensity of soil enzymes and polysaccharides secreted by roots to cope with abiotic stress. At the same time, soil carbon sequestration is affected by the adverse environment, which restricts the input of organic matter into the soil.