Shifts in soil seed bank and plant community under nitrogen addition and mowing in an Inner Mongolian steppe

Atmospheric nitrogen (N) deposition and land management practices (e.g. mowing) are two major threats to grassland soil seed banks and plant communities. However, the interactive effects of N addition and mowing on soil seed banks and plant communities are poorly quantified. A six-year field experiment was used to examine the responses of soil seed banks and plant communities to N addition (10 g N m(-2) year(-1)) and mowing (once a year) in a temperate steppe in northern China. Soil seed bank and plant community structure were investigated with laboratory germination and visual examination. Mowing reversed the depletion of seed bank size under N deposition at soil depths of 2-5 cm and 5-10 cm. The main effects of N addition and mowing increased 1.1 species (0.25 x 0.25 m(2)) independently, but no interactions of N addition and mowing on seed richness were detected at soil depths of 5-10 cm. Nitrogen addition had few effects on plant cover, but mowing suppressed it by 11.5%, mainly by decreasing grass cover. Nitrogen addition stimulated plant height by 6.25 cm by enhancing grass height whereas mowing did not influence it. Nitrogen addition decreased 2.8 plant species due to negative effects of N addition on forb. The positive effects of mowing on forb richness exceed negative effects of mowing on grass richness, leading to a net increase of 2.8 plant species with mowing. Our findings suggest that changes in soil seed bank size under N deposition can be strongly modulated by land use. Both N deposition and mowing can increase seed richness in deep soil (5-10 cm). Mowing stimulated, but N deposition suppressed, plant species richness. This is potentially important for understanding the influences of land use and environmental changes on soil seed banks, with subsequent effects on plant community dynamic.