Global climate change usually involves simultaneous and continuous changes under different environmental conditions.However,it is very difficult and expensive to explore those climate change in manipulative experiments.Applying models can help us to understand the responses of ecosystem structure and function to global climate change.To explore the effects of climate change on carbon processes in grassland and cropland on the Loess Plateau,the Terrestrial Ecosystem (TECO) model was applied to identify patterns of ecosystem carbon processes in response to changes in CO2 concentration,temperature,and precipitation.The results showed that net primary production (NPP) and heterotrophic respiration (Rh) increased with temperature up to +4 ℃ and then declined,except that the highest Rh in cropland ecosystem was at 0 ℃ (ambient conditions).Net ecosystem exchange (NEE) showed the opposite trend with the lowest value at +4 ℃,and the highest C sequestration was at +4 ℃ in both systems.Changes in precipitation and CO2 concentration affected the responses of NPP,Rh,and NEE to temperature change.The NPP,Rh,and NEE became more sensitive to temperature change with increased precipitation.Changes in precipitation affected the turning points of temperature responses for NPP,Rh,and NEE in the grassland ecosystem,but not in the cropland ecosystem.With increased CO2 concentration,the patterns of NPP,Rh,and NEE became flatter when temperature change was greater than +4 ℃.The interaction between increased precipitation and warming had the highest relative strength in terms of effects on NPP,Rh,and NEE,with values of 51.0％ and 30.0％,51.3％ and 16.6％,and-46.1％ and-28.9％ in the grassland and cropland ecosystem,respectively.The interaction between increased precipitation and increased CO2 concentration had the smallest relative strength in terms of effects on NPP,Rh,and NEE,with values of 2.4％ and 7.5％,3.7％ and 3.4％,and 8.1％ and-9.0％,in the grassland and cropland ecosystems,respectively.Three-factor interactions were not significant for these ecosystems.Our results suggest that carbon dynamics are less sensitive in the cropland ecosystem than in the grassland ecosystem to interactions among climatic factors under climate change.

In order to study the distribution and changes of soil organic carbon (SOC)and inorganic carbon (SIC)and total carbon with grassland potential degradation following altitudes along Helan Mountain,mean-while explore their relationships with environment factors of climate,vegetation and soil,we collected soil samples and plant samples in three grassland types at different altitudes along Helan mountain in Alxa,Inner Mongolia,China.The different soil indexs which mainly included soil pH,Soil organic carbon,total carbon, soil total nitrogen (TN),total phosphorus,available nitrogen and soil bulk density were measured.The rela-tionships between soil carbon with environment factors of climate,vegetation and soil were analyzed by inte-grated partial correlation analysis.The results showed,as the altitude increasing,soil organic carbon content and density increase and were expressed as grassland types:steppe> desert steppe> steppe desert.However, soil inorganic carbon and total carbon content and density increase gradually with altitude increasing,but it slightly decreased at the grassland at altitude of 2100 m.Integrated partial correlation analysis showed TN was significantly correlated with soil organic carbon.While,the factors affecting soil inorganic carbon varied great-ly.Soil bulk density was significant correlated with soil inorganic carbon and annual rainfall and annual average temperature were the main factors too.Because soil carbon density was influenced greater by soil carbon con-tent than soil bulk density,similar to soil carbon content,soil carbon density in steppe was significantly greater than soil carbon density in steppe desert.Additionally,if the grassland at the higher altitude changes to the sit-uation as the lower altitude,soil organic carbon content and density decreased,but soil organic and total carbon content and density decreased only when the grassland types changed.The whole research revealed that the degradation of the grassland influenced both soil organic and inorganic carbon content and density,and the soil development influenced the soil organic carbon characteristics too.

“生态安全”是国家安全的重要组成部分,是维系一个国家经济社会可持续发展的基础。阿拉善位于内蒙古自治区最西部,总面积27万km2。辽阔的阿拉善植被是阻挡西北风沙入侵我国北方地区的重要天然屏障,长期以来,由于气候和人为影响,阿拉善植被遭到严重破坏。草地“三化”面积达到58 630.53km2,占全盟可利用草场面积的57.1%,生产力急剧下降。