关键词: 库布齐沙漠, 生物结皮, 优势藻, 形态, 核糖体内部转录间隔区（ITS）

Abstract:

Due to the strong interference of global warming and human activities, arid and semi-arid regions in China are facing a series of ecological and environmental issues. The Inner Mongolia Autonomous Region is a major sandy region in China. The Kubuqi Desert, situated in the north of the Ordos Plateau in Inner Mongolia and being the desert closest to Beijing, holds a pivotal position in the fields of desert ecology that cannot be underestimated. Biological soil crusts play multifaceted ecological roles in desert ecosystems. Moss crusts, which represent an advanced stage of biological crust succession, contribute significantly to desertification control. However, biological crusts formed through natural succession are characterized by slow development and are highly susceptible to interference and damage. The artificial cultivation of biological crusts has emerged as a novel approach to desertification control, relying on the intricate interactions between biological and abiotic factors. Algal crusts possess a variety of ecological functions, such as improving the physical and chemical properties of the soil, enhancing enzyme activity, and accelerating ecological restoration. Cyanobacteria and green algae are the principal desert algae that play crucial roles in the ecological functions of algal crusts. The formation and development of artificial algal crusts can facilitate the succession of biological crusts, leading to relatively rapid emergence of stable moss crusts. The selection and breeding of excellent algal strains are fundamental to the construction of artificial biological crusts. However, the research on the diversity of algal components in the biological crusts of the Kubuqi Desert has received insufficient attention, and there is a dearth of relevant theories and practices regarding the artificial cultivation of biological crusts. In this study, in June, August, October, and December 2023, well-developed biological crust samples were systematically collected from open areas of Stipa gobic and Stipa glareosa vegetation, Artemisia ordosica vegetation, enclosed Artemisia ordosica vegetation, and Salix cheilophila vegetation along the eastern edge of the Kubuqi Desert, using sterile shovels. For each type of sample, including bare sand, algal crusts, and moss crusts, surface-layer soils (1‒2 cm) and lower-layer soils (2‒5 cm) were collected, with each sample area measuring 10 cm×10 cm, and three replicates were taken for each sample to ensure statistical reliability. During the experimental phase, crust algae were cultured in BG11 liquid medium in an artificial climate incubator. The isolation and purification of crust algae were meticulously performed using the spread-plate and streak-plate methods. Identification was performed under an optical microscope using the traditional morphological identification methods. Simultaneously, DNA was extracted from 20 purified algal strains, followed by PCR amplification for molecular identification. Their phylogenetic positions were verified using molecular biological techniques. The species richness of cyanobacteria and green algae, as well as the composition of dominant algae in the biological crusts of different vegetation types and seasons in the Kubuqi Desert, were quantified using a standardized counting method. This study aimed to establish a robust theoretical foundation for the screening of excellent algal strains for artificial construction of biological crusts in the Kubuqi Desert. The results indicated the following: 1) 78 species of cyanobacteria and green algae belonging to 27 genera across 14 families were identified in the biological crusts of the Kubuqi Desert. Specifically, there were 40 species of cyanobacteria, classified into 10 genera in 5 families, and 38 species of green algae, belonging to 17 genera in 9 families. Statistically significant differences were observed in the species richness of algae in biological crusts among different vegetation types and seasons. The species richness of cyanobacteria and green algae in naturally developed and open Artemisia ordosica and Stipa gobic and Stipa glareosa vegetation was lower than that in artificially restored Salix cheilophila vegetation. Among them, the species richness of cyanobacteria and green algae in enclosed Artemisia ordosica vegetation, which featured dense vascular plants, was the lowest when compared with non-enclosed vegetation. The species richness of algae in artificially restored vegetation was significantly higher than that in naturally developed vegetation, whereas the species richness of algae in enclosed vegetation was significantly lower than that in non-enclosed vegetation. Notably, the species richness of cyanobacteria was significantly reduced in enclosed Artemisia ordosica vegetation. In terms of seasonal variation, the species richness of algae was significantly lower in winter than in spring, summer, or autumn. The species richness of cyanobacteria peaked in August, whereas that of green algae signifantly decreased. 2) At the genus level, the dominant algae in the biological crusts of the Kubuqi Desert were generally consistent. The cyanobacteria were primarily represented by Lyngbya, Oscillatoria, and Microcolus, whereas the green algae were Chlorella, Chlamydomonas, and Scenedesmus. Among these, Lyngbya mucicola, Oscillatoria subtilissima, Microcolus vaginatus, Microcolus sp. of cyanobacteria and Chlorella vulgaris, Chlamydomonas maramuresensis, Scenedesmus javaensis, and Scenedesmus platydiscus of green algae were the dominant algae in the Kubuqi Desert. 3) The morphological characteristics of the 20 purified algal strains were precisely described and the ribosomal internal transcribed spacer (ITS) was sequenced. Phylogenetic trees of 2 cyanobacteria and 18 green algae were constructed based on the detection data, thereby verifying their phylogenetic positions. Through a comprehensive synthesis of the dominant desert algae in various deserts and sandy lands, both in China and abroad, Microcolus vaginatus was found to be prominent. The dominant species were mainly concentrated in the genera Lyngbya, Oscillatoria, Phomidium, Chlorella, Chlamydomonas, and Scenedesmus. This study comprehensively explored the species diversity of cyanobacteria and green algae in the biological crusts of different seasons and vegetation types in the Kubuqi Desert. It accurately identified the dominant cyanobacteria and green algae in these biological crusts, purified the dominant algal strains, and verified the phylogenetic positions of the purified algal strains using molecular biological methods. This study aims to offer a theoretical basis for the scientific screening and efficient purification of algal strains for the artificial construction of biological crusts in the Kubuqi Desert. This will contribute to the accurate selection of dominant algal strains under appropriate seasonal and vegetation conditions, thereby enhancing the success rate and ecological benefits of artificial biological crusts. Moreover, this study enriches and improves the research on algae in the biological crusts of desert ecosystems.

Key words: Kubuqi Desert, biological crust, dominant algae, form, ITS