2.2 Experimental design
A two-factor (seed source of region × soil moisture treatment)
experiment was carried out at Nankai University. The experiment was
established in plastic pots (14.5 cm in diameter and 12.5 cm in height),
with a mixture of vermiculite and nutrient soil (1:1) as culture
substrate. Seed source of region included the eastern, middle and
western regions of S. krylovii distribution area, with three
populations per region (Table 1). Soil moisture treatment was quantified
by volumetric water content (VWC) which was estimated by an
ECH2O Check (Decagon Devices, Pullman, WA, USA).
Considering that the water retention of nutrient soil used in this study
and the corresponding soil water potential in their local habitats in
the Inner Mongolia Steppe, we set VWC to 20% for control treatment,
15% for light drought treatment and 8% for heavy drought treatment.
Each treatment included 18 pots (6 pots per population), and each pot
included 4 six-month healthy seedlings and each seedling was similar in
size (about 10 tillers, uniform height (10 cm), and root length (12
cm)). In total, there were 162 pots (3 seed source of regions × 3 soil
moisture treatments × 18 replications). To exclude precipitation, all
pots were randomly placed under a five-meter-height rain-proof shed, and
their positions were changed every week to avoid position effects. The
experiment lasted 72 days from June 20 to September 14, 2022.