『Abstract
　Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha^-1 year^-1; MN, 100 kg N ha^-1 year^-1; LN, 50 kg N ha^-1 year^-1) on soil respiration compared with non-fertilization (CK, 0 kg N ha^-1 year^-1), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q10 varied within 1.70-1.74) but was slightly reduced in MN treatment (Q10 = 1.63). N fertilization increased soil CO2 emission in the order MN＞HN＞LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P＜0.05) and reached a marginally significant level for LN (P = 0.059 ＜0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July-September 2007). Furthermore, the differences between the three fertilization treatments ad CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007 - June 2008). The annual total soil respiration was 53, 57, and 24％ higher than in the CK plots (465 g m^-2 year^-1). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July-September 2008, P＞0.05). The pairwise differences between the three N-level treatments were not significant in either year (P＞0.05).

Keywords: Soil respiration; Nitrogen fertilization; Temperate grassland; China』

Introduction
Materials and methods
　Site description
　Experimental design
　Soil respiration rates
　Environmental factors
　Data analysis
Results
　Seasonal variations of soil respiration rates
　Cumulative soil respiration rates
　Relationships between soil respiration rates and temperature and water conditions
Discussion
　The effect of nitrogen fertilization on seasonal variations of soil respiration rates
　The effect of nitrogen fertilization on temperature or moisture dependency of soil respiration rates　
　The effect of nitrogen fertilization on cumulative CO2 effluxes
Conclusions
Acknowledgments
References