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).