**2.3 Soil seed bank analyses**

Transect line sampling was conducted, as previously described [19, 20]. Specifically, random arrangement of two 10 m long sample lines were placed in each sample plot in April 2013 using a customized soil seed bank sampler with equidistant 1 m sections that were then sampled at 0–2 cm, 2–5 cm, and 5–10 cm depths. Soil samples (n = 360) were placed in bags and transported back to the laboratory where they were then used for soil seed bank germination experiments. Indoor soil seed germination experiments were conducted as described previously [21]. The sampling area of each sample plot was 0.8 m2 , and the total sampling area of the six sample plots was 4.8 m<sup>2</sup> . Briefly, direct germination measurements were used to estimate the portion of the seed bank capable of producing germinating seeds and the species composition of the SSB. Seedling germination can usually detect more than 90% of the species within the SSB of grassland ecosystems [22]. Soils were

**Figure 1.** *The locations of the sampling sites.*

sun-dried inside of a greenhouse then sieved to remove litter, roots, rocks, and other debris. Soil samples were evenly spread and then placed in pots (42 cm � 28 cm � 15 cm) with a soil thickness of 1.5 cm with seed-less sand used as matrix at the bottom of the pots at a height of 10 cm.
