**1. Introduction**

Biological invasion is a global problem, resulting in major changes to ecosystem diversity and stability [1,2]. The introduction of exotic plants into new habitats within a certain period and with limited space can cause environmental degradation, resource shortages, natural disasters, and other phenomena, thus altering the original ecological balance and reducing biological diversity [2–5]. When alien plants are introduced into a new environment, they exhibit strong adaptability and growth advantages due to changes in the external environmental factors [1,6,7], ultimately causing changes to the soil carbon and nitrogen cycle and the microbial structure.

Bamboo is widely regarded as one of the most economically useful species in the 21st century and is mainly distributed in the tropical and subtropical regions of the Asia-Pacific, Africa, and Latin America [8]. Moso bamboo (*Phyllostachys edulis*) is a very important forest resource in southern China [9]. Moso bamboo has the biological characteristics of rapid growth and a strong reproductive capacity. Its rhizomes are also characterized as being strongly aggressive and being able to gradually spread into the adjacent forest vegetation, resulting in an expansion phenomenon in the stand, thus forming a mixed forest or even a pure bamboo forest [10].

The expansion of moso bamboo can seriously threaten the adjacent forest vegetation and lead to the death of the surrounding forest vegetation, thus altering the vegetation community structure and reducing biodiversity [9]. The expansion of moso bamboo reduces soil organic matter carbon [8,11], nitrogen transform rates [10,12], and the changes to soil microorganisms mainly depend on the original soil type [9,13,14]. The expansion of moso bamboo also causes significant changes in the emissions of the soil greenhouse gases nitrous oxide and carbon dioxide [15–19].

Soil microorganisms are an important component of forest ecosystems and play a significant role in the mineralization of soil organic matter and nutrient cycling [20]. Fungi and bacteria are the main components of the soil microbial community, and their abundance and diversity are directly affected by soil properties and environmental factors [21], which are of grea<sup>t</sup> significance for energy conversion and material circulation [22]. Different environmental conditions and vegetation types can change the structure and function of the soil microbial community [23,24]. Changes in stand types have different effects on the community structure, root exudates, litter quantity and quality, and nutrient availability. Therefore, in recent years, soil microbial diversity has become a pertinent issue in the field of ecology [25]. Fang et al. [26] studied changes in the soil nitrogen cycle, as affected by Japanese cedar and moso bamboo, by adding biological inhibitors. However, there are few studies on soil microbial diversity under different expanding stages.

The expansion of moso bamboo into surrounding forests will reduce species diversity and alter the vegetation type [27]. Vegetation-species composition plays an important role in soil microbial-community structure [28,29]. The expansion of moso bamboo leads to alterations in the forest-species composition, which has a direct impact on soil microbialcommunity structure, in turn affecting plant development, plant-community composition, and ecosystem functioning. Here, soil microbial communities' compositions as well as litter and soil carbon and nitrogen status, during different expanding stages of moso bamboo, were studied. We predicted that (1) litter and soil carbon and nitrogen status differ with expanding stages of moso bamboo; (2) soil microbial-community compositions altered differently between microbial and fungal communities, in response to the expansion of moso bamboo. We expected clearly separated changes in both biotic compositions and abiotic characteristics along the expanding stages of moso bamboo.

#### **2. Materials and Methods**
