Characteristics of soil seed banks of a typical grassland in the loess hilly region of Ningxia ecologically restored by contour trenching

The study of soil seed banks is of great significance in the ecological restoration of grasslands. We investigated the density characteristics, species diversity, and similarity to the aboveground vegetation of the soil seed bank, and the characteristics of seed and soil factors using a canonical correspondence analysis (CCA) model for the 0-5, 5-10, and 10-15 cm soil layers under different restoration measures in a typical steppe grassland in Ningxia. We selected sites that had been subject to enclosure for 15 years (F15), contour trenching for 1 year (S1), contour trenching for 3 years (S3), contour trenching for 6 years (S6), contour trenching for 10 years (S10), or contour trenching for 15 years (S15); grazed grassland (F0) was used as a control. The results showed that 1) The number of plant species was the highest in S1, followed by that in F15, and the lowest in F0 and S10. There were no significant differences in seed bank plant species with increasing years, but the seed bank constituents shifted from annuals to perennials. 2) The density of the soil seed bank was the highest in F15, intermediate in S3 and S15, and the lowest in F0. The density of the soil seed banks was characterized using table clustering. With the increase in the duration of contour trenching, the total seed bank showed an up-down-up trend. 3) The similarity coefficient between the seed bank and aboveground vegetation in the various treatments was generally low, at 0.380.55. F15 had the highest similarity with S3, and the lowest with S10 and S15. 4) CCA showed that soil available potassium, moisture content soil total phosphorus , and were the main factors affecting the distribution of soil seed banks in this area. Our study showed that, compared with grazed grassland, restoration through contour trenching can increase the number of species and density of soil seed banks in a typical grassland, but the effect is still lower than that of enclosing the grassland.