Effects of nitrogen amendments on spring annual plant distribution, primary production, and species diversity in a semi-arid environment were studied. The ecological responses of spring annual plant species to nitrogen differed between species, and between sites. The distribution of each species in a control transect was wider than in a nitrogen-treated transect. Annual plant species diversity at each station in the control transect was higher than that of the nitrogen-treated transect. The lower site of the Lower Basin Slope areas had the highest species diversity (0.94 for the control and 0.84 for the nitrogen-treated), and the Upper Basin Slope area, shrub vegetation zone, had the lowest species diversity (0.27 for the control and 0.05 for the nitrogen-treated) in both transects. Inorganic nitrogen in the nitrogen-treated transect soils was consistently higher than that in the control transect soils; however, the former showed more fluctuation from station to station than the latter. Above-ground biomass of spring annual plants in the nitrogen-treated transect was consistently higher than that in the control at each station. The maximum above-ground biomass in the control and nitrogen-treated transect was 24.4±4.4 gm−2 and 61.2±10.6 gm−2, respectively. Variations in above-ground biomass along the transect did not parallel with the variation in inorganic nitrogen in soils and species diversity.
dominance-diversity curve nitrogen amendment species diversity spring annual plant