The temperate steppe located in semiarid and arid regions in northern China is the typical vegetation type across the vast area in the Eurasian content and is sensitive to climate change and land use (Christensen et al. , 2004; Niu et al ., 2008). This comprehensive research project is sponsored by Institute of Botany, Chinese Academy of Sciences with an attempt to examine responses of the semiarid temeprate steppe to multiple driving factors (Mowing, N deposition, changing precipitation regime, and climtic warming) of global change.

Chinese Academy of Sciences.

State Key Laboratory of Vegetation and Environmental Change.

Each plot was divided into four 44 m×28 m subplots with 1 m -wide buffer zone . There were totally 32 subplots in this study. The four subplots within each plot were randomly assigned with four treatments of nutrient addition, including no nutrient addition (C), nitrogen addition (N) treated with u rea in 2005 and NH3NO4 in 2006 and 2007 (10 g N m-2 y-1 ), phosphorus addition (P) treated with calcium phosphate ( 5 g P2O5 m-2 y-1 ), and combined additions of both N and P (NP, with the same form and amount of N and P with those in the N and P treatments ). Nutrient was added once a year in July.

Within each FC and NF subplots, three small subplots with 10m × 15 m size were set up for water treatments, among which one was treated as spring water addition (May and June), one was treated as summer water addition (July and August), and one was treated as unwatered treatment. Within each small subplot, six sprinklers were evenly arranged into two rows with the distance between any two sprinklers being 5 m. Each sprinkler covered a circular area with a diameter of 3 m; therefore, the six sprinklers covered the 10m ×15 m small plot. Fifteen mm of water was applied weekly. The total water amount of 120 mm was added each year (about 30% of annual mean precipitation in the study site) to the spring and summer water addition treatments.

Within each 10×15 m plot, four 3×4 m subplots were treated as warmed and control plots with two replicates. The warmed subplots have been heated continuously since 28 April 2005 using 165 × 15 cm MSR-2420 infrared radiators (Kalglo Electronics Inc, Bethlehem , PA , USA ) which were suspended 2.5 m above the ground. In the unwarmed control plot, one “dummy” heater with the same shape and size as the infrared heater was suspended 2.5 m high to simulate the shading effects of the heater. Thus, there were six replicates for each treatment (control, warming, increased precipitation, and warming plus increased precipitation).