Intensity and Duration of Nitrogen Addition Jointly Alter Soil Nutrient Availability in a Temperate Grassland

Increasing N input can alter soil nutrient availability and influence plant growth. Previous studies focused on N addition effects on N and P availability, while less on other mineral nutrients. Besides, how N addition duration affects nutrient availability has remained unclear. Based on a simulative N deposition experiment in a typical steppe with four N addition levels (0, 2, 10, and 50 g m(-2) yr(-1)) under three N addition duration (2, 5, and 10 years), we determined contents of 10 mineral nutrients in surface soils. In the 0-10 cm soil, short-term N addition (2-year) significantly increased exchangeable Ca (+7.2%) and decreased exchangeable Mg (-22.5%) as compared with the control, while decreased available Fe, Cu, and Zn, but increased Mn remarkably (+80.4%). Medium-term N addition (5-year) significantly raised soil total N and available Fe, Mn and Cu, while decreased total P and exchangeable Ca, Na and Mg. The response patterns of these nutrients were largely similar in the 10-20 cm soil, but were weaker and significant only at high N inputs (50 g m(-2) yr(-1)). Long-term N addition (10-year) significantly decreased contents of total base cations (K, Ca, Na, Mg) and micronutrients (Fe, Mn, Cu, Zn) by an average of 32.1% and 20.4%, respectively, across the two soil depths. Influences of pH and plant growth on micronutrients showed remarkable differences among different duration of N addition. These findings indicate that intensity and duration of N addition jointly alter soil nutrient availability and this should be considered in soil nutrient-cycling modeling.