| We examined the effect of experimental warming and nitrogen addition in a desert steppe, in which the constructive species is Stipa breviflora and some companion species is Artemisia frigida, Cleistogenes songorica. Infrared heaters were employed to increase soil surface throughout the May, 2006, nitrogen fertilizer (NH4NO3,nitrogen contents is 33%～35%) was applied in rain season early July. Soil temperatures at depths of 0 cm , 7.5 cm , 15 cm , 30 cm and 50 cm increased by 1.32℃, 0.92℃, 0.88℃, 0.80℃and 0.74℃in the warmed plots, respectively. There was significant difference (P﹤0.05) between warmed and control plots on the soil temperature. The result showed obvious effects on soil temperature and an increase in ambrent air temperature.Soil moisture had similar seasonal fluctuation in warmed and control plots; although soil moisture content of 0 -30cm in warmed plot was higher than control, soil moisture content under warming had no obvious change with the control (P>0.05). Warming and nitrogen additon influenced soil nitrogen obviously, interactions of experimental warming and nitrogen addition significantly increased the total nitrogen (N) content of soil (P﹤0.05), and the total phosphorus (P) content and potassium (K) content of soil were also higher in warming and nitrogen addition plots than in control , but no siginificant difference between control and treatments. Contents of NH4+-N and NH3--N showed increases under the experimental warming, especially NH4+-N contents. NH3--N content of 0-30cm had great increase under interactions between experimental warming and nitrogen addition. Not only experimental warming but also nitrogen addition, soil respiration rate did not significantly increase, although soil temperature with depths had positive correlation with soil respiration rate.Soil greenhouse gas (GHG) fluxes of CO2, CH4 and N2O in a Desert Steppe showed the CO2 and N2O emission fluxes, CH4 sink. Warming had no effect on greenhouse gas (GHG) concentrations or emissions in a xeric Desert Steppe environment. Here, the primary influence on GHG's was associated with season. Nitrogen addition advanced the N2O emission fluxes in all seasons, CO2 emission fluxes deceased in summer and CH4 sink had no obvious change. Experimental warming made reviving in advance and lasting days of phenological periods prolong in warmed plots. All treatments expressed similar compositions primarily, as the constructive species and some companion species, warming and N addition did not significantly influence those in plant community. Experimental warming improved the evenness of plant community, but the richness and species diversity reduced. The Margalef richness index (Ma) increased and the Pielou evenness (JP) and Shannon-Wiener diversity index (H') of plant community decreased under nitrogen addition plot. Experimental warming increased aboveground biomass in the early growth stage and decreased it in faster growing and latter stages. Seen from the functional group, perennial grasses and forbs had stable compositions, but compositions and number of shrubs, half shrubs, small half shrubs, annuals and biennials were unsteadiness, where aboveground biomass in warmed plots was much difference with control. Nitrogen addition may enhance aboveground biomass obviously from latter growth stages. Underground biomass were no significant difference whether experimental warming or nitrogen addition. The main factor was soil moisture content of 10-20cm depth that affected aboveground and underground biomass. The relationship between aboveground biomass and functional group diversity was of a unimodal pattern irrespective of air temperature treatment in some degree. Change of plant litter and seed rain was not significantly correlated with temperature and nitrogen addition.Artemisia frigida had significant response to warming; the lengths of phenological growth periods for Artemisia frigida did not show an increasing trend in warmed plots, even disappeared in early September. Summed dominance ratio (SDR3) of Artemisia frigida was lower (P0.05) in the warmed plot than in the control plot, Artemisia frigida is more sensitive to temperature changes than other species.
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