Experimental design
We conducted the field experiment in 2007 at the Pasture Ecological
Research Station of Northeast Normal University, Changling, Jilin
province, China (44°45’ N, 123°45’ E). The original soil of experimental
field (aeolian sandy soil, pH = 8.3) at the station had been used
annually for many years, thereby low in nutrients availability (organic
C 3.1 mg kg–1, available N 21.0 mg
kg–1, and available P 1.1 mg kg–1)
during the growth season of 2007 (Zhao et al., 2010). Seeds of A.
theophrasti were collected from local wild populations near the
research station in late August 2006 and dry stored at
-4oC. We applied a randomized block design, with
germination timing (GT) as the main factor, and block as the sub-factor.
The whole plot was divided into twelve 2 × 3 m sub-plots, which were
randomly assigned with four GT treatments and three blocks. Seeds ofA. theophrasti were sown at an inter-planting distance of 10 cm
on June 7, June 27, July 17 and August 7, as four GT treatments of
spring (GT1), late spring (GT2), summer (GT3) and late summer (GT4). The
treatments of germination timing accorded with the time range of
germination of A. theophrasti in its nature habitats in northeast
of China. Most seeds emerged four days after sowing. Seedlings were
thinned at four-leaf stage and plots were hand-weeded when necessary and
watered regularly.