Experimental design
On 15 July 2018, plants of S. breviflora were dug from a
temperate grassland area located at Horinger county, Inner Mongolia,
China (111°50′E, 40°29′N). Then, they were hand separated into two types
of experimental subjects containing ramets with similar morphological
size: individual with single ramet (C1) and individual with three ramets
connected by rhizomes (C2). Twenty individuals of each experimental
subject were transplanted to one square pot (60 cm length × 35 cm width
× 18 cm height) filled with soil mix containing 20% field soil (from
Horinger) and 80% vermiculite ((Mg, Fe, Al)3[(Si,
Al)4 O10 (OH)2].
4H2O) at the greenhouse of the College of Grassland,
Resources, and Environment of the Inner Mongolia Agricultural
University. There was a total of 12 square pots for C1 and 12 square
pots for C2. The chemical properties of experimental soils were shown in
Table 1. In the greenhouse, there was 14 h light/10 h dark photoperiod.
The air temperature was 26 ± 2 ℃ and 20 ± 2 ℃ for day/night,
respectively.
The experimental design was a
standard Taguchi L8(27) arrays
including four factors such as
nitrogen (N), phosphorus (P) and water (W) and cluster fragmentation (C)
and three interactions (N × P, N × W and P × W).
Each of four factors had two
levels, and there was a total of 8 treatments (Table 2). This experiment
used NO3NH4 and
NaH2PO4·2H2O as N and P
fertilizer with the addition concentrations
of 15 mg N / kg and 120 mg N / kg
and 2 mg
P2O5 / kg and 24 mg
P2O5 (low level/high level)
respectively. Water additions included
25 % ~ 30 %
field moisture capacity of mixture (FMC)
and 75 % ~ 80 %
FMC, and cluster fragmentation consisted of
individual with single ramet and
individual with three ramets (Table 2). MINITAB 18.0 (Minitab, Inc.,
State College, PA, USA) software was employed in this data analysis
step. The experiment was repeated 3 times with 5-day interval between
them. Before treatments, individuals were allowed to grow for 21 days to
establish roots. Each experimental period lasted 17 weeks. The nitrogen
and phosphorus additions were repeated every 20 days, while water
additions were repeated every 3 days.