| As consequences of human activities, the increasing of both Earth’s surface temperature and atmospheric N deposition has impacted on plant community, soil and ecosystem C cycle over the past two centuries. As one of the most important terrestrial biomes, grassland accounts for approximately40%of the Earth’s land area play critical roles in regulating global C balance, but human on the understanding of grassland ecosystem, especially on the desert grassland ecosystem, is still a lack of awareness under the global climate change. The study relies on the experimental base of Inner Mongolia Siziwangqi desert sreppe pastoral Academy as a research platform, the seasonal responses of on the desert grassland community, soil and ecosystem C exchange to warming and management regime were studied. According to the study of global change and terrestrial ecosystem relationship, a reliable theoretical basis was provided. The study was initiated in June2006with a split-plot experimental design with warming as the main-plot effect and N addition as the sub-plot effect.Compared with CK, soil temperatures at depths of0cm,10cm,20cm and30cm increased by2℃,0.87℃,0.86℃and0.77℃in the warmed plots, respectively. With the increasing of soil depth, the soil temperature was decreased. The survey of soil nutrients in2007-2009, we found the warming and N addition didn’t change soil organic carbon content. However, warming and N addition didn’t soil total N content. The positive linear interaction was found between NH4+and the depth of temperature, and between NO3-and the depth of temperature. With the increasing of temperature, both NH4+and NO3-were also increased. No significantly were detected on the effect of total NH4+by warming, N addition or their interactions from in2007to in2009. Warming significantly increased soil NO3-concentration both in2008(P=0.02) and in2009(P=0.01). whereas no effects of warming was detected in2007(P=0.36).Three years’ study (2006-2008) showed the evident temperature was linearly and positively correlated with mean soil respiration in three years, however, elevated temperature had not impact on soil respiration. A close relationship between the natural conditions and the effect of the nitrogen fertilizer to the desert grassland among which the rainfall was the main factor which had a positive effect to the nitrogen fertilizer, while in high precipitation season. N addition promoted soil respiration. N addition significant increased plant below-ground biomass,and a significantly positive correlation was detected between belowground biomass and soil respiration (P<0.001).We found that warming decreased biomass production of several species and consequently the total aboveground biomass. Similarly, divergent species responses to N addition were aggregated to an increase in aboveground net primary productivity (ANPP) under N addition in2008with more rainfall in the growing season. Based on principal response curves (PRC) analysis, N addition lead to a shift in dominance from perennials to annuals by the third year, but warming did not affect species composition. Nitrogen (N) addition also increased [N] and total N content of aboveground plant tissues, suggesting enhanced forage quality by N addition. We also found an interactive effect of warming and N addition on ANPP and total plant N content. Seasonal precipitation patterns strongly affected the temporal changes of community productivity as well as its response to N addition, indicating that the desert steppe community was co-limited by water and N.Net ecosystem CO2exchange on behalf of the ecosystem to absorb or release of CO2capacity, both ecosystem gross primary productivity and ecosystem respiration decided on net ecosystem CO2exchange. The unprecedented global warming and nitrogen (N) deposition impacts ecosystem carbon (C) cycling. From2007to2009, a field study was conducted to evaluate the effects of warming, N addition, and their compound effect on net ecosystem exchange (NEE), ecosystem respiration (ER) and gross ecosystem productivity (GEP), in the Desert Steppe in Inner Mongolia, China. N addition increased NEE, ER and GEP, but the increase of GEP was higher than increase of ER during the growing season, leading a net C sink status during the study. Warming increased ER, but had no effect on NEE and GEP during the study. Seasonal mean NEE, ER and GEP had positive linear correlations with both soil moisture and peak aboveground biomass. In this dry desert steppe of Inner Mongolia, N addition increased net C storage during the growing season, but the warming had no significant effect on NEE in a short term. |
