## 1 Introduction  
Desertification is a serious ecological and environmental problem faced by China and even other countries in the world, affecting about one-sixth of the world's population [1]. Desertification is of grave concern because of its threats to human survival and societal development [2]. Drylands cover more than one-third of the Earth's continental surface and thus constitute the most extensive terrestrial biome on the planet [3]. Carbon storage in drylands account for 36% of the total global carbon storage [4]. Arid ecosystems are often characterized by low energy and nutrient availability of soil microbes and the availability of N and P generally limits primary productivity and microbial activity. Research on the quality of desert soil has recently changed focus from the basic physical and chemical properties of soil and the sand-fixing mechanism of sandy plants to soil microbial characteristics [5;6]. It is very important to study soil microbes in desertified and arid areas, especially after adding feldspathic sandstone into sand so that we may better understand if and how desertification can be reversed. Changes in land conditions inevitably alter soil microbial metabolism and energy flow [7;8]. Studying the soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and its stoichiometry after adding feldspathic sandstone into sand can inform us about how soil nutrients are transformed. For example, [PERSON] et al. [9] proved that the change of MBC:MBN was mainly related to abiotic variables, while the changes of MBC:MBP and MBN:MBP were mainly related to changes in soil microbial community structure. Thus, soil microbial communities respond differently to soil resources. Additionally, [PERSON] et al. [10] reported that MBC:SOC increased as aforested lands aged. This indicates that soil microbial stoichiometry can adaptively change with resource stoichiometry [11], and that soil microbial quotient can reflect stress effects and can be used as ecological physiological indicators. Similarly, [PERSON] and [PERSON] [12] suggested that higher MBC:MBN may reflect a larger overall investment in C-rich structural cellular material, while [PERSON] et al. [13] suggested that lower MBN:MBP may reflect the higher allocation to P-rich ribosomes. Therefore, it is necessary to investigate the relationship between soil nutrient resources and microbial biomass, especially the ratio of microbial biomass C:N:P after mixing feldspathic sandstone and sand. Recently, the most widely measured and extensively studied extracellular enzyme activities have included \(\beta\)-1,4-glucosidase (BG), cellobiohydrolase (CBH), and \(\beta\)-D-xylopyranoside (BX), indicators of energy (C) demand, an indicator of N demand known as \(\beta\)-1,4-N-acetylglucosamineimalidase (NAG), acid or alkaline phosphatase (AP or AKP), and indicators of P demand [3;14;15]. The potential activity of these extracellular enzymes can reflect the biogeochemical equilibrium between nutrient requirements of microbial assemblages and environmental nutrient availability [16;17;18]. For example, [PERSON] et al. [19] suggested that soil microbes would secrete more AP enzymes to meet the P demand in soils with low P availability. [PERSON] et al. [3] found that lower BG:NAG and MBC:MBN ratios indicated greater soil microbial demand for N versus C. [PERSON] et al. [20] reported that BG:AP and (NAG + LAP):AP of typical steppes and desert steppes were lower than those of meadow steppes, implying that typical steppes and desert steppes had stronger P limitations. Therefore, studying the soil extracellular enzymes and their stoichiometry can provide an important step in assessing the stoichiometry and energy limitation of soil microbial metabolism after mixing feldspathic sandstone and sand. As one of four large sandy lands in China, the Mu Us Sandy Land has a fragile ecological environment and is one of the most severe desertification areas in northern China [2].