Experimental design
The experiment was conducted in 2007 at the Pasture Ecological Research
Station of Northeast Normal University, Changling, Jilin province, China
(44°45’ N, 123°45’ E). Seeds were collected from local wild populations
near the research station in late August 2006 and dry stored at
-4oC. We used a split plot design, with soil
conditions as the main factor, density and block as a sub-factor. Two
large plots were assigned as two (Infertile and Fertile) soil
conditions, each was divided into nine 2 × 3 m sub-plots and randomly
arranged with three treatments of densities and blocks. The treatment of
infertile soil conditions as a plot was established using the original
soil of experimental field at the station that had been used annually
for many years (aeolian sandy soil), and the treatment of fertile soil
conditions was set up by covering the other large plot with 5-10 cm
virgin soil transported from a nearby meadow with no cultivation history
(meadow soil), with contrasting nutrient contents of the two soil
conditions (Wang et al. 2017). Seeds of A. theophrastiwere sown on June 7, 2007, with three inter-planting distances of 30, 20
and 10 cm, to reach target plant densities of 13.4, 36 and 121 plants
per m-2, assigned as Low, Medium and High density
treatments respectively. Most seeds emerged 4 d after sowing. Seedlings
were thinned to the target densities at four-leaf stage. Plots were
hand-weeded when necessary and watered regularly.