『Abstract
　To clarify responses of plant and soil carbon (C) and nitrogen (N) pools in grassland ecosystem to N addition, a field experiment was performed in a grassland in Keerqin Sandy Lands, Northeast China. We investigated vegetation composition and C and N pools of plant and soil (0-30 cm) after five consecutive years of N addition at a rate of 20 g N m^-2 y^-1. Vegetation composition and species diversity responded dramatically to N addition, as dominance by C4 perennials was replaced with C3 annuals. Carbon in aboveground pool increased significantly (over two-fold), mainly due to the increase of the C in aboveground living plants and surface litter, which increased by 98 and 134％, respectively. although soil C did not change significantly, the root C pool decreased in response to 5 years of N addition. The total ecosystem C pool was not significantly impacted by n addition because the large soil pool did not respond to N addition, and the increase in aboveground C was offset by the decrease in root C pool. moreover, N addition significantly increased the aboveground N pool, but had no significant effects on belowground and total ecosystem N pools. Our results suggest that in the mid-term N addition alters the C and N partitioning in above- and belowground pools, but has no significant effects on total ecosystem C and N pools in these N-limited grasslands.

Keywords: Carbon partitioning; Carbon pool; Keerqin Sandy Lands; Nitrogen limitation; Sandy grassland; Species composition』

Introduction}
Materials and methods
　Site description
　Experimental design
　Sampling and analyses
　Data processing and analysis
Results
Discussion
　Nitrogen effects on semi-arid grassland vegetation
　Ecosystem carbon and nitrogen pools
Acknowledgments
References