2.2 | Experimental design
Four stress factors, including high-temperature (T), drought (D), nitrogen deficiency (N), and phosphorus deficiency (P), at 2 levels per factor, for 16 treatments, of which CK was the control group the treatment conditions for each group are shown in Table 1. As a full nutrient solution, Hoagland’s solution was used (table S1). In the reference method (Torres-Rodriguez et al., 2021, Zhao et al., 2005), the phosphorus content is set to 0 mM for the phosphorus stress treatment, and the nitrogen content is set to 0 mM for the nitrogen deficiency stress treatment. The corresponding concentrations of KH2PO4, Ca(NO3)2, KNO3, and NH4NO3 were adjusted to 0%, respectively. The lacking Ca and K in the deficit solutions were CaCl2 and KCl, respectively, while the remaining components of Hoagland’s solution remained unchanged. Based on ground temperature data from the S. miltiorrhiza cultivation base in Zhongjiang, Sichuan, the temperature was chosen with 25℃/20℃ (day/night) for the normal conditions and 42℃/35℃ (day/night) for the high-temperature stress condition. The water holding capacity (WHC) was 75% for normal moisture conditions and 30% for drought stress conditions (Liu et al., 2011).