Effects of rotation grazing time on the characteristics of soil seed bank in desert steppe.

Exploring the characteristics of soil seed bank under seasonal grazing plays an important role in the reasonable use of desert steppe. We examined seed bank species composition, density, vertical distribution, diversity in the soil of 0-5, 5-10, 10-15 cm soil layers and the relationship with vegetation and soil environmental factors in Ningxia desert steppe. The treatments included enclosure (FY), traditional time rotation grazing (FG), delayed to start rotation grazing (YG), early to end rotation grazing (TG), delayed to start and early to end rotation grazing (YT) and free grazing (ZY). The results showed that there were nine families and 21 species in the soil seed bank in the study area. The species composition of soil seed bank in TG seed bank with 13 species was the largest, while FY and ZY soil seed banks had the least, with 8 species, respectively. The den-sity of ZY soil seed bank was significantly higher than that of FY, YG, TG and YT. The number of perennial species seeds in the soil seed bank of FY was the largest, reaching 32.0%, while that in the ZY was the least, only 12.4%, mainly with sexually reproduced annual weeds. Soil seed bank was mainly concentrated in the 0-5 cm surface layer. With increasing soil depth, the size of soil seed bank decreased. The dominance and diversity of soil seed bank were the highest in FY, while the dominance, diversity and uniformity were the lowest in ZY. The similarity between soil seed bank and aboveground vegetation was generally low. In contrast, the FG and ZY seed banks had higher similarity with vegetation, and the FY was the lowest. Soil moisture, organic matter, total nitrogen concentration, total phosphorus concentration, and soil bulk density were the main soil factors affecting soil seed bank. Compared with traditional whole year free grazing, seasonal four-zone rotation grazing could increase species richness and abundance of perennial plants in soil seed bank of desert steppe, as well as the total species richness, diversity and uniformity of the seed bank. Although the effect sof seasonal four-zone rotation grazing on seed bank was not as good as the long-term enclosure grassland, it was of great significance to the utilization and protection of desert steppe.