| In the face of increasingly large climate change and energy substitution pressure, low carbon economy is rapidly becoming the focus of attention of all circles at home and abroad. The characteristics of a low carbon economy is to reduce greenhouse gas emissions, construction of low energy consumption, low pollution based economic development system, including low carbon energy system, low carbon technologies and low carbon industry system. Land resources as the carrier of all human activities, is the material basis for human survival and development, the development of human society cannot do without the land use and transformation, this relationship can be said to the people and land is the most basic relations of production throughout the history of the development of human society. Land use playing an important role in increasing the content of atmospheric carbon dioxide, its impact after the burning of fossil fuels. According to the Intergovernmental Panel on climate change assessment report, since 1850 global greenhouse gas emissions of 1/3 directly caused by changes in land use, such as large amount of woodland, grassland, farmland, wetland into construction land, thus directly led to the decline in carbon sequestration capacity and carbon source volume rapid growth. With the rapid development of industrialization, urbanization, carbon emissions due to land use change also showed a rising trend. Therefore, in the background of the development of low carbon economy, low carbon research how to guide the optimization of land use structure to realize the land use change type, plays an important role in technological innovation, land use management.Based on the above consideration, this article under the sustainable development theory, system theory, the land ecological economic theory, man-land relationship theory and location theory, by using system analysis method, qualitative and quantitative methods, theoretical research and empirical analysis method of combining, specific analysis of the relationship between land use change and the carbon cycle, and based on this proposed optimization of land use structure of low carbon oriented. The main contents include the following aspects:(1) study on the relationship between land use change and the carbon cycle. Relations between the way, intensity, types and carbon balance in different land use research. Analysis of the natural disturbance carbon emission of land use change and the carbon cycle factors, land use, land use change is directly related with the carbon cycle, namely, land use, land structure and land use intensity change impacts on carbon cycle; a brief analysis of the indirect land use change and the carbon cycle, the land use of all anthropogenic carbon source emission type bearing. Analysis of the changes in carbon storage and carbon emissions of national land use structure change, with the help of the previous research results, discusses the optimization of land use structure of carbon emission reduction effect. (2) analysis of the effects of carbon emissions under different management. First introduces the concept of management, land management is the main way of management of land, the different types of land use intensity of use. Then analyzed under different management effects of carbon emissions to the types, and puts forward the calculation method of the carbon density and carbon emission coefficient. (3) land use structure optimization based on low carbon target. First discusses the low carbon on the guiding role of the land use structure optimization, embodied in the overall control of carbon source on regional land use, mainly rely on to contain the expansion of construction land, realize the scientific control of regional construction land carbon emissions. On the other hand reflected in respect of enhancing carbon sequestration capacity of regional land ecological system, rely mainly on increasing woodland, grassland, wetland carbon to carbon capture and storage area of land, thereby effectively reduce land net carbon emissions. Then elaborated the principle of land use structure optimization of low carbon targets, including the reduction of sink enhancement principle, integrity principle, the principle of inheritance, sustainable principle, the dynamic principle, the principle of suit one’s measures to local conditions, macro, meso, micro combination principle. The mathematical model and the linear programming model for structure optimization, to determine the maximum carbon savings and emissions targets a minimum as a function of structural optimization, and set up the constraints. Focus on the different scenarios of land use structure optimization schemes were studied, according to the scenario analysis method, divided three kind of situations, namely the general situation, a more negative scenario, the ideal scenario. And analysis of the different scenarios, the most likely use management style (use intensity), and different situations of land carbon density and carbon emission coefficient were determined. (4) in Chifeng city as an example, analyzed the effects of carbon emissions over the class of different management methods, on this basis, estimates for the different scenarios of Chifeng city classification of soil carbon density and carbon emission coefficient, and then to optimize the land use structure, and finally put forward different scenarios in Chifeng City land utilization strategy under low carbon. (5) put forward the main conclusion of the study and implementation of policies and measures for land use of low carbon.Through theoretical and empirical research, we draw the following conclusions:(1) land use natural disturbance carbon emission factors, including climate, soil physicochemical properties, biological factors and nitrogen deposition factors, which is the basis of carbon exchange between land and natural systems. The relationship between land use change and the carbon cycle in two aspects, one is the change of land use and carbon emissions and carbon sequestration, another is the change of land use. Among them, the land use change caused by carbon emissions, and can be divided into land use effects of carbon emissions type changes, including forest land to arable land, woodland to grassland change, change of grassland to farmland, agricultural land to construction land change and wetland to his conversion type and land management of change impact on carbon emissions, including forestry management strategy, farming strategy, pasture use policy, land use policy, land use and management behavior of construction; and carbon sequestration effects of land use changes mainly in returning farmland to forest and grass forest land and grassland are the main carbon absorption. In addition, because the land use is of greater complexity and spatial heterogeneity, so the land use change on the carbon cycle, regional differences, the influence of carbon source/sink, large uncertainties still exist.(2) In all kinds of field management, fertilization can affect the content of soil organic matter and its changes from two aspects. One is to improve the soil aggregate structure, effects of soil microbial activity, thus affecting the soil organic matter decomposition; two is to increase crop yield, improve crop (stubble and roots) returning amount. Grassland of different management methods (including the reclamation of grassland, grassland fire over grazing, etc.) significant effect on soil carbon pool. The reclamation of grassland will lead to grassland soil, soil organic carbon is released, the loss of the total carbon carbon in soil 30%-50%; overgrazing of grassland soil respiration will promote, in addition to animal trampling can increase the soil bulk density, causing the organic carbon release. The forestry sector mainly through the following four kinds of management activities to achieve the emission reduction, forest carbon sink. One is to reduce deforestation, afforestation, maintain or increase the forest area; two is to optimize the age structure, improved forest tree varieties, maintain or improve the stand level carbon density (carbon storage per unit area); the three is to strengthen the management, reduce forest fires, pests and diseases, improve or maintain the landscape level carbon density; four is the forestry biomass fuel alternative to fossil fuels. Each type of emission reduction sink enhancement activities and cost efficiency has its specific time scale, the biggest short-term benefit is to avoid or reduce carbon emissions (i.e. reduce deforestation and degradation, forest fire and forest pest control etc.). Study on carbon emission effect is still in the discussion stage construction level of different land use, there are certain differences of different calculation results. Taking the Inner Mongolia Autonomous Region as the object of study, found that there is a positive relationship between the two, the correlation coefficient is up to 0.99, the level of land intensive utilization increased 1 percentage points, carbon emissions will increase by 0.126 unit. Visible, the estimated construction with a simple relationship between the level of land intensive use and carbon emissions may exist deviation. Because, in different stage of the development of the country, construction land expansion is still exist many problems in the area of development, and the construction land expansion energy consumption carbon offset greatly the level of intensive use of construction land increase the carbon emission reduction effect. So in the data still show along with raising the level of intensive use of land for construction, carbon emissions.(3) Various land use types used in different situations of the management in different ways, for the land, from the fertilizer input point of view, more is the pursuit of high economic benefit, the fertilizer input will be greater. For grassland, from grazing intensity, the more the pursuit of high economic benefit, the higher grazing intensity. For forest land, economic development has little effect on forest management, most of the time effect of harvesting intensity of forest. But with the increase of ecological construction in our country, a series of measures of closing hillsides to facilitate afforestation, forest protection zones have expanded, woodland management means and measures are in a relatively stable state, by the economic development influence. For construction land, from the strength point of view, economic development with the impact of management on the construction is positive, which will promote the economic development of the capital and labor resources, so as to improve the level of intensive use of construction land; but at the same time, economic development also contributed to the expansion of building land. From both the carbon impact analysis, the impact of the latter is clearly more directly, the impact is greater.(4) The combination of empirical findings, there exist obvious differences under different management of all types of carbon density and carbon emission coefficient. 100cm soil fertilizer, organic carbon storage of single application of organic fertilizer, organic fertilizer, straw and no fertilizer were 91.3,95.7,104.2,100.6,87.7, t·hm-2. Fertilizer organic fertilizer treatments significantly increased soil organic carbon storage, followed by a single application of organic fertilizer, straw, chemical fertilizer, no fertilizer effect is the worst. From the different management methods on the impact of soil carbon balance, if we consider the annual CO2 emission from soil, the fertilizer organic fertilizer and organic manure plots, soil carbon balance is positive, the soil every year a surplus of 655.4 and 100.3 kg C·hm-2, other treatment of organic carbon showed a loss of status, the chemical fertilizer without the input of organic manure, the largest amount of deficit, as 2244.8 kg C·hm-2, followed by no fertilization data, deficit of 2070.8 kg C·hm-2, straw returning could increase the amount of stubble, reduce the CO2 emission from soil, soil organic carbon losses for the 1785.7 kg C·hm-2.Effect of different grazing intensity and grassland on soil organic carbon significantly, Wai grazing plots of organic carbon content in samples, was significantly higher than that of over grazing and cultivation plots, especially in the surface above 20cm soil layer, the differences are obvious. Reclamation has significantly decreased the content of soil organic carbon, its effect on the carbon storage and overgrazing. From the variation of soil organic carbon in the soil surface (0-10cm) point of view, the change of soil organic carbon was the biggest, fenced plot 33.24 g·kg-1, reclaimed sample is only 21.61 g·kg-1, decrease about 1/3, and the reclamation of grassland to farmland after the conclusion of the loss in the total amount of original soil carbon 30%-50%.Woodland in the specific management way by calculating, forest carbon reserves of 2466.04 ×104t, forest area of 130.01 X 104hm"2, a rough calculation of the vegetation carbon density of 18.96 t·hm-2, calculation results in line with the T in 6.47～118.14 t· hm-2, forest vegetation (not including shrubs) annual carbon sequestration capacity of 2090700 tons, forest soil carbon sequestration capacity of 61.1 X 104t, the annual forest carbon sequestration totaled 270.07 ×104t, forest land area of about 171.72×104hm-2, forest carbon sink coefficient calculated for 1.57 t·hm-2, combined with the woodland emission coefficient 0.007 t·hm-2, get the land annual net carbon emission coefficient of -1.563t·hm-2.That the relationship between the level of land intensive use and carbon emissions of Chifeng city construction, energy consumption of carbon emissions and the level of intensive use of construction land are positively related,1 percentage point increase with the level of land intensive using of construction, carbon emissions will increase by 0.006 unit.(5) based on analysis of the effects of carbon emissions under different management measures on different scenarios, Chifeng city classification of soil carbon density and carbon emission coefficient, and then optimize the land use structure, the results show that, the comprehensive three scenarios, comparing the carbon storage and carbon emissions in visible, carbon savings a negative scenario relative to the other two scenarios of minimum, and carbon emissions are the largest. The ideal scenario, land carbon savings amount is maximum, minimum carbon emissions. Thus, in the scientific and rational land management basis, to optimize the land use structure, can effectively curb land use carbon emissions, increasing carbon sinks.(6) the paper finally proposed to promote the policies and measures of land use low carbon. Including the indirect effects of various land use policy of the carbon cycle, such as the size of the supply of land, land price leverage adjustment, land reserves and land supply mode.In the conclusion, the main ideas, the conclusion of the thesis and the innovations, limitations and prospected related research.
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