Spatial distribution patterns of the soil seed bank of Stipagrostis pennata (Trin.) de Winter in the Gurbantonggut Desert of north-west China

The aim of this study was to investigate the spatial distribution patterns of soil seed bank of Stipagrostis pennata (Trin.) de Winter during different seasons in the Gurbantonggut Desert of north-west China. Results indicated that spatial patterns of the soil seed bank of S. pennata were similar to the distribution patterns of its associated standing vegetation, and there was a significant variation in soil seed densities among the different parts of the dunes. The highest soil seed density was found on the top of sampled dunes and in the soil of the underlayers of standing vegetation beds of S. pennata. The number of seeds stored in the soil decreased with distance from established stands of this grass species. Moreover, during secondary seed dispersal, which is air-borne in the windy season, a small proportion of seeds was also trapped by other plant species. Furthermore, the directional density distribution of seeds was strongly associated with the directions of the prevailing threshold wind ( 6 m s−1), and higher soil seed densities usually occurred on the leeward side of the vegetation stands. Based on these investigations, wind is, probably, the key factor in forming the spatial patterns of S. pennata seed banks in the region. On the other hand, grazing affected the quality and quantity of S. pennata seed storage, as a result of delayed development and the above-ground shoots being damaged by grazing. This occurred in spring to early summer, which is the most suitable growth season for the grass. Nevertheless, grazing had little influence on the spatial distribution patterns of the seed bank over all seasons. Germination trials showed that the percentage of viable soil seeds increased continuously throughout summer and autumn. The results also revealed the clear ecological characteristics influencing the population distribution of S. pennata.