Lichens are stable extracellular symbiotic life systems formed by lichen-forming fungi as the constructive species, with algae or cyanobacteria as associated symbionts, also known as mycobiont-photobiont symbionts [1][2]. Beyond the core constructive and associated symbiotic species, stable lichen mycobiont-photobiont communities host a diverse array of epiphytic microorganisms; accordingly, lichens are regarded as miniature microecosystems and a typical manifestation of widespread biodiversity in nature [2]. The origin of lichens dates back to the Early Devonian, approximately 400 million years ago, making them one of the earliest symbiotic organisms to colonize terrestrial habitats on Earth [3][4]. According to estimations lichen-dominated vegetation covers around 8% of the global land surface [3][5].

Saxicolous lichens refer to lichen taxa colonizing stable surfaces of rocks and various mineral substrates, mainly divided into two categories: epilithic lichens and endolithic lichens [3]. Their distinctive thallus structures endow them with exceptionally high and unique ecological functions. In alpine high-elevation zones, saxicolous lichens participate in regional water regulation and nutrient accumulation, and are critical to sustaining the structure and stability of alpine ecosystems. As classic pioneer organisms, they accelerate rock weathering and soil formation on high-altitude plateaus, optimize the microhabitat environment, and lay a foundation and favorable conditions for the primary succession of plant communities [6][7].

Climate projection data predict a global temperature rise of 4˚C by 2100, accompanied by dramatic shifts in precipitation patterns [8]. Against the backdrop of global climate change, climatic conditions, soil properties and precipitation regimes in alpine high-elevation regions are undergoing corresponding transformations, which substantially alter the community composition and species diversity patterns of lichens [9][10]. While saxicolous lichens exhibit extreme environmental tolerance, capable of surviving harsh habitats with intense solar radiation, severe drought and high temperatures, certain species are highly sensitive to environmental fluctuations. Therefore, species richness and community diversity of saxicolous lichens can serve as excellent bioindicators of climate change in alpine regions [11][12]. In summary, saxicolous lichens are key pioneer organisms in extreme habitats characterized by cold alpine conditions, aridity and intense ultraviolet radiation, and they perform irreplaceable vital functions in ecological processes including ecosystem succession, pedogenesis, and the conservation of regional biodiversity.

Since the 21st century, research on the impacts of climate change on biodiversity has become a core focus in ecological research. In recent years, affected by global climate change, the temperature and precipitation in the Eastern Pamir Plateau have shown a continuous increasing trend, leading to accelerated glacier melting. From 1972 to 2011, the glacier area and storage in this region decreased by 5.79% and 6.69%, respectively, which has posed certain threats to regional habitat environments and biodiversity [13][14]. Located in the eastern Pamir Plateau, the Taxkorgan Nature Reserve of China sits at the junction of the Tianshan, Kunlun, Karakoram, and Hindu Kush mountains. It connects two global wildlife biodiversity hotspots—the Himalayas and Central Asian mountains—making it one of the critical species gene pools and an ecologically vital area for biodiversity conservation [15].

The reserve’s distinctive geographic position and natural environmental conditions create ideal habitats for saxicolous lichens. As a result, this area has become a natural experimental platform and core research hotspot for lichen diversity, drawing widespread interest from lichenologists and ecologists worldwide. While climate warming and glacial retreat have enlarged the extent of exposed bedrock and generated additional suitable microhabitats for saxicolous lichens, the mechanisms driving their impacts on lichen species diversity and community structure remain poorly understood. In this context, investigations into saxicolous lichen diversity within the region can supply fundamental empirical data to unravel community assembly and diversity maintenance mechanisms of saxicolous lichens across arid zone of northwestern China. Against this backdrop, the present study aims to characterize the species diversity of saxicolous lichens and document their distribution patterns along elevational gradients within the reserve.

This study systematically investigated the species diversity, composition, and elevational distribution patterns of saxicolous lichens across five elevational belts in the Sereketaxi region of Taxkorgan Nature Reserve, Eastern Pamir Plateau. A total of 24 saxicolous lichen species belonging to 13 genera and 8 families were recorded, with distinct community diversity and compositional differentiation along the elevational gradient. The research results confirmed a typical mid-elevation diversity peak of saxicolous lichens at 4316 m, accompanied by significant elevational variation in species richness and community structure, while species evenness remained stable across altitudinal zones. These findings reveal unique assembly characteristics of rock-dwelling lichen communities in alpine arid plateau habitats, providing empirical evidence for understanding lichen distribution adaptation mechanisms under extreme high-altitude environments.

The relatively moderate species richness recorded in this study is comprehensively shaped by habitat characteristics, survey limitations, and taxonomic identification difficulties. Compared with the higher lichen species richness documented in the Western Tianshan Mountains with more diverse habitat types [23], the lower species number in the study area is primarily attributable to the single alpine bare-rock habitat and extreme arid-cold climatic conditions of the Eastern Pamir Plateau, which strictly filter lichen species and only allow highly stress-tolerant taxa to survive. In addition, the exclusive focus on saxicolous lichens (excluding terricolous and corticolous lichens) and the limited sampling range of high-altitude inaccessible areas further restrict the total recorded species richness. Crucially, crustose lichens, which dominate the local community, exhibit highly similar morphological characteristics and tiny thalli, leading to great challenges in accurate morphological identification [24]. Despite the modest total species richness, the recorded lichen community is stable and well-adapted to local extreme habitats, fully representing the core characteristics of saxicolous lichen resources in the Eastern Pamir alpine desert ecosystem.

Community composition analysis verified that crustose lichens are absolutely dominant in the study area, consistent with the universal distribution rule of saxicolous lichens in alpine arid mountain regions [25][26]. Genera including Acarospora and Aspicilia constitute the dominant species pool, which is closely related to the unique adaptive traits of crustose lichens. Crustose lichens tightly adhere to rock substrates, effectively resisting strong alpine ultraviolet radiation, extreme drought, severe temperature fluctuations, and wind erosion [3]. Their special thallus structure enables efficient utilization of limited water vapor and mineral nutrients on barren rock surfaces, making them the pioneer and dominant organisms colonizing high-altitude bare rocks. At the species level, Rusavskia elegans and Candelariella oleifera occurred in all sampling plots with the highest relative coverage, demonstrating their absolute dominant position in the local lichen community. This study further confirms that these two species have extremely wide ecological amplitude and strong environmental adaptability to alpine arid oligotrophic habitats [27][28]. The stable existence of widespread dominant species is the core foundation for maintaining the structural stability of saxicolous lichen communities in extreme plateau habitats, and these species can serve as key bioindicators for monitoring environmental changes in the Eastern Pamir region.

A core finding of this study is the significant nonlinear elevational pattern of saxicolous lichen diversity, with a prominent mid-elevation diversity hotspot at 4316 m. The species richness, Shannon-Wiener diversity index, and Simpson dominance index all peaked at this elevation, presenting a typical unimodal elevational distribution pattern. This pattern is highly consistent with the lichen diversity distribution rules observed in the Himalayan Arc, Western Tianshan Mountains, and Argentine alpine mountainous regions [23][29][30], indicating that the mid-elevation peak is a universal diversity pattern for mountain saxicolous lichens across different arid and alpine regions. We propose two synergistic mechanisms to explain this core distribution pattern: microhabitat heterogeneity and environmental filtering balance.

First, the 4316 m elevational belt exhibits the highest microhabitat heterogeneity. Compared with the low-elevation zone (4168 - 4287 m) with relatively single rock substrate and severe drought stress, and the high-elevation zone (4454 - 4486 m) with intense ultraviolet radiation, low temperature, and frequent strong winds, the mid-elevation belt features balanced light availability, moderate temperature and humidity conditions, and diverse rock microhabitats. Such heterogeneous microenvironments can accommodate lichen species with different environmental adaptation strategies, supporting higher species richness and community diversity. Second, this elevation forms a balanced environmental filtering threshold. Low-elevation habitats are constrained by extreme aridity and substrate barrenness, limiting the survival of sensitive lichen species; high-elevation habitats are governed by low temperature and strong radiation stress, eliminating species with weak stress resistance. In contrast, the mid-elevation zone avoids extreme environmental constraints, forming a suitable habitat for most local saxicolous lichens, thus shaping the regional biodiversity hotspot.

NMDS ordination, PERMANOVA test, and β-diversity analysis collectively verified significant compositional differentiation and species turnover of saxicolous lichen communities along the elevational gradient, which is a key innovative finding of this study. The community composition of each elevational belt formed independent clustered groups in the NMDS analysis, confirming distinct community segmentation driven by elevation. Notably, the highest species dissimilarity and strongest species turnover occurred between the 4287 m and 4316 m belts, rather than between distant elevational zones, indicating that lichen community differentiation does not follow a simple linear elevational variation pattern. We hypothesize that local microhabitat conditions override pure elevational differences in driving community differentiation. The slight differences in rock substrate properties, slope aspect, micro-scale temperature and humidity, and vegetation coverage between adjacent elevational belts trigger significant species replacement, resulting in abrupt community compositional changes at the 4287 - 4316 m elevation transition zone.

Additionally, this study found a typical overlapping distribution phenomenon of low- and high-elevation species at the 4316 m hotspot belt, which is a very common ecological pattern in mountain elevational gradient research. The mid-elevation zone not only accommodates endemic mid-altitude lichen species but also allows partial low-elevation drought-tolerant species and high-elevation radiation-resistant species to coexist, further explaining the highest species richness and unique community characteristics at this elevation. Meanwhile, the non-significant difference in Pielou evenness index across all elevational belts indicates that although elevation and microhabitat differences significantly regulate species richness and community composition, they have a weak regulatory effect on the relative distribution uniformity of individual species. The stable evenness further proves that dominant species such as Rusavskia elegans and Candelariella oleifera can stably occupy niche spaces in all habitats, maintaining the relative balance of community structure in different elevational environments.

Under the background of ongoing global climate warming, the Eastern Pamir Plateau is experiencing continuous temperature rise, increased precipitation, and accelerated glacier retreat [13][14]. Glacier melting exposes a large number of new bare-rock substrates, providing potential new habitats for saxicolous lichens. However, the specific mechanisms by which climate change alters microhabitat conditions, drives species turnover, and reshapes lichen community elevational patterns remain unclear. Combined with the findings of this study, we infer that future climate warming may further expand suitable habitats for saxicolous lichens, but excessive temperature rise and hydrological changes may break the mid-elevation environmental balance, potentially shifting the diversity hotspot and altering existing community differentiation patterns.

This study has certain limitations. First, we only set fixed elevation sampling belts and did not conduct continuous gradient monitoring, failing to capture fine-scale dynamic changes of lichen communities. Second, this study only analyzed the macroscopic elevational distribution pattern of lichen diversity but did not quantify the driving effects of microhabitat factors (substrate physicochemical properties, micro-temperature and humidity, radiation intensity) on community assembly. Finally, the lack of species accumulation curve analysis cannot fully evaluate the sufficiency of the current sampling design, and a small number of rare species may not be fully captured.

In summary, this study systematically clarified the species composition, diversity characteristics, and elevational differentiation pattern of saxicolous lichens in the Sereketaxi region, revealing that the coupling of macro environmental filtering and microhabitat heterogeneity is the core driving mechanism of lichen community distribution. The research results fill the gap in basic data of saxicolous lichen diversity in the Eastern Pamir Plateau and provide a theoretical basis for lichen resource conservation and biodiversity maintenance research in arid zone of northwest China. Future research should supplement species accumulation curve analysis to optimize sampling reliability, integrate multi-dimensional microenvironmental monitoring data, and further explore the response mechanisms of saxicolous lichen community assembly to climate change and microhabitat variation on the alpine plateau.

(1) A total of 24 saxicolous lichen species belonging to 13 genera within 8 families were recorded in the Sereketaxi Zone of Taxkorgan Nature Reserve. The genera with the highest species numbers are AcarosporaA. Massal. and Aspicilia A. Massal., while Rusavskia elegans(Link) S.Y. Kondr. & Kärnefelt and Candelariella oleifera H. Magn. represent the dominant species in the study area.

(2) Significant differences in saxicolous lichen diversity were detected across elevation bands. Both the total species number of transects and diversity indices at the sampling plot scale indicated that the elevation band at 4316 m was the diversity hotspot for saxicolous lichens in this study, presenting an overall mid-elevation peak pattern.

(3) Pronounced differentiation in community composition existed among elevation bands. The combined results of Bray-Curtis dissimilarity, Jaccard index, PERMANOVA and NMDS ordination revealed significant species turnover and community segregation between different elevation bands. The 4316 m elevation band possessed both high species richness and strong community uniqueness.

Overall, the species composition and distribution of saxicolous lichen at different altitudinal zones in the Sereketaxi Zone of Taxkorgan Nature Reserve can be generalized as a dual regulation model driven by “macro environmental filtering and microhabitat heterogeneity modulation”. Future research could further integrate multi-dimensional datasets including chemical properties of rock substrates, microscale dynamic monitoring of temperature and humidity, slope gradient and aspect of sampling sites, to thoroughly unravel the community assembly mechanisms of saxicolous lichens on the eastern Pamir Plateau and their response patterns to global climate change.

We would like to express our gratitude to the management office of the Taxkorgan Nature Reserve for allowing us to conduct field investigations.

Liming Liu (writing original draft, formal analysis); Fenghui Guo (formal analysis); Maierhaba Aimudula (data curation); Wukelai Duosimubayi (data curation); Ainiwaer Tumier (formal analysis, project administration, supervision, writing-review & editing).

Natural Science Foundation of Xinjiang Uygur Autonomous Region, China [Grant No. 2025D01C24]; the National Natural Science Foundation of China [Grant No. 32560001] and Xinjiang University Training Program of Innovation and Entrepreneurship for Undergraduates [S202610755178] provided funding for this study.

Table S1. The coverage of 24 saxicolous lichens on 15 sampling plots.

Table S2.Prequency of 24 saxicolous lichens on 15 sampling plots.

Table S3. Important value of 24 saxicolous lichens on 15 sampling plots.