## 1 Introduction
This means that geographical location, topography, environment, and vegetation are important factors influencing the structure and diversity of microbial communities. Meanwhile, the succession of vegetation causes significantchanges in the structure, function, and diversity of soil microbial communities [14; 18]. However, current research on soil ecosystem microorganisms mainly focuses on forest soil, degraded grassland soil, and soil under different orchard and mining conditions for different species, habitats, and depths [16]. There is less research on the composition and diversity of microorganisms in fragile ecosystems caused by differences in ecological forest vegetation. Specifically, in recent years, ecological forest restoration modes have seen a wide range of cultivated areas for artificial grasslands such as apricot (_Armeniaca sibirica_ L., AR), peach (_Amygdala davidiana_ ([PERSON], AM), alfalfa (_Medicago sativa_ L., MS), and peach-apricot-alfalfa (AR&AM&MS). The impact of these restoration modes on the structure and diversity of soil microbial communities deserves further research. Furthermore, soil enzymes are active participants in soil biochemical processes, and their activity can indirectly reflect the diversity of soil microbial functions. Enzymes produced by microorganisms and plants are closely related to soil energy flow and nutrient cycling, and they respond quickly to soil changes [19; 20]. These enzymes are considered to be direct participants in the carbon, nitrogen, and phosphorus cycles [20]. Many studies have confirmed the high correlation between soil enzyme activity and bacterial and fungal communities [21; 22]. Fungal communities have a greater impact on phosphatase, urease, and protease activities, while bacterial and actinomycete communities have a greater impact on sucrase. Microorganisms and plant root systems can secrete various enzymes to supply the soil, ensuring the smooth progress of various biological metabolic processes in the soil [21]. In addition, soil extracellular enzymes are special enzymes secreted by microorganisms into the soil and obtain energy and nutrients from the soil. They play a regulatory role in the decomposition of organic matter by soil microorganisms and the absorption and utilization of soil nutrients such as C, N, and P by microorganisms [23]. For example, \(\beta\)-1,4-glucosidase (BG) is mainly used to obtain carbon; \(\beta\)-1,4-N-acetylgl-ucosaminidase (NAG) is mainly used to obtain nitrogen; and acid or alkaline phosphatase (AP) is mainly used to obtain phosphorus [20]. Taken together, exploring the relationship between soil enzyme activity and soil organisms can help determine the response of microbial communities to the ecosystem, providing insight into ecosystem structure. Moreover, many scholars have used high-throughput sequencing technology to thoroughly and accurately investigate the distribution and diversity of soil microbial communities under different land use patterns [12; 24]. This mainly involves metagenomic sequencing technology, among which Illumina Solexa technology is more commonly used [25]. Given this, this work aims to investigate the impact of different restoration modes on the physicochemical properties and the structure and diversity of soil microbial communities. Furthermore, the response of soil microorganisms to land use changes or soil resource availability will be explored, and the mechanism of the impact of different restoration modes on the structure of soil microbial communities will be further revealed. Based on the characteristics of vegetation distribution in the fragile area of the Loess Plateau, combined with the land use pattern, this work proposes using abandoned land (AL) as a control treatment, with AR, AM, MS, and AR&AM&MS as typical sample fields. The main highlight is the systematic study of the community structure and functional diversity of soil microorganisms (including bacteria and fungi) under different ecological forest restoration modes.