## 1 Introduction  
Human-induced, large-scale land-use and cover change may bring severe ecological and climatic consequences [1; 2]. Regional water and energy balances, as well as ecosystem carbon budgets, have been shown to be significantly influenced by large-scale land-use change [3; 4; 5]. Balancing regional energy and carbon budgets concerns not only regional and global climate stability, but also the well-being of local residents and regional sustainable development. The pastoral farming ecotone of the temperate steppe in Inner Mongolia is a typical area with intense land-use and cover change in China. Naturally grazed steppe used to be the dominant land-use type in this area but is now being rapidly and extensively replaced by other land uses, particularly steppe cultivation and grazing exclusion [6]. In response to global climate change, the cultivation boundary in the Northern Hemisphere is moving gradually north [7; 8; 9; 10]. Moreover, a large portion of the typical temperate steppe in central and eastern Inner Mongolia is situated in the pastoral farming ecotone in northern China, which is under increasing cultivation pressure driven by growing economic and food demand [11]. By 2000, the new cultivation area in the eastern Inner Mongolia steppe had surpassed 1000 km\({}^{2}\)[11]. Moreover, the integrity and stability of ecological functions of this area are critically important, as the Inner Mongolia temperate steppe constitutes an important ecological protective barrier for most of the developed area of northern China. In particular, the area serves to protect Beijing from devastating sand storms. Arid and semi-arid ecosystems have also been shown to be easily damaged by overgrazing [12; 13; 14]. As a consequence, the government has invested great efforts in local ecological construction and restoration, and large areas of steppe in this region have been involved in related projects. By 2006, the grazing exclusion area implemented in the Beijing and Tianjing sand-source control project reached 66.93 \(\times\) 10\({}^{4}\) ha [15]. With an area of 3.55 \(\times\) 10\({}^{8}\) ha, steppe in China represents 41.7% of the national territory and 7.2% of the total area of steppe in the world, ranking second globally [16]. The biomass carbon pool of China steppe is 3.32 PgC, and the soil carbon pool also accumulates a considerable amount of carbon [17]. The potential large-scale land-use and cover change of the vast steppe in northern China may have major impacts on the budget of this huge carbon pool, which could have a correspondingly substantial impact on the regional environment, and even on the global climate [18; 19]. The vegetation carbon-use efficiency (CUE) is the proportion of total primary production (GPP) fixed to net primary production (NPP) and can be used quantitatively to describe the ability of vegetation to fix atmospheric CO\({}_{2}\) in the surface ecosystem [20]. The CUE of different vegetation is considered a constant value close to 0.5 [21; 22]. However, it has been noted in studies that CUE varies widely from 0.23 to 0.83, even within forest ecosystems alone [20]. Understanding the mechanism of the regulation of CUE under different land-use and management patterns is essential to enhance understanding of the influence of human activities on the carbon budget of ecosystems. These key parameters and the relationships obtained would substantially help to increase the accuracy of related models. The GPP is the sum of NPP and autotrophic respiration (Ra), while Ra together with heterotrophic respiration (Rh) comprise the ecosystem respiration (Re) [23]. Therefore, the key to measuring the ecosystem CUE accurately during experimental determinations is the accurate division of Re into Ra and Rh [24; 25]. In addition, Re also can be roughly divided into two parts: belowground respiration (Rb) and aboveground respiration (Rab), according to the location in which the respiration takes place [26].