Soil Nutrient Responses to One Year of Simulated Global Warming and Nitrogen Deposition on the Songnen Meadow Steppes, Northeast China

Soil nutrient processes and functionalities play significant roles in affecting global changes. Herein, two key global change factors, warming and nitrogen deposition were used to examine the soil nutrient responses under simulated global change conditions on the Songnen meadow steppes of Northeastern China. Through onsite investigations and laboratory analysis, soil nutrient responses were evaluated under short-term simulated global changes as follows: (1) The soil net nitrogen mineralization rate (NMR) responded positively to warming with a statistical significance of about 24%, in the presence of about a 2degC increase in soil surface temperature on the Songnen meadow steppes. The NMR did not respond significantly to N deposition or N deposition in combination with warming. NMR remained at a relatively stable level during the growing season of the year; (2) warming had no significant effect upon either TN or AN, while N deposition in combination with warming had a significant effect upon AN but not upon TN. TN and AN both displayed seasonal variability during the year; (3) warming, N deposition and their combined action had no significant effect upon AP. However an increase in N deposition in our study had a positive effect upon TP with an increase of about 40%, TP responded with no significance to warming or warming and N deposition combined. AP did not display seasonal variability while TP levels decreased swiftly at the end of the experimental period; (4) Our data indicates that warming and N deposition may both add to future warming and aggravate local non-point sources of pollution.