Profiling the Bacterial Diversity in a Typical Karst Tiankeng of China

Karst tiankeng shapes the differential composition and structure of bacterial and fungal communities in karst land

Karst tiankeng are important biodiversity conservation reservoirs. However, the unique habitats of karst tiankeng affect microbial community structure remained poorly understood. In this study, we collected soil samples from karst tiankeng (TK) and karst land (KL) and subjected to high-throughput sequencing. Based on the classification of the total, abundance, and rare taxa for bacteria and fungi, a multivariate statistical analysis was carried out. The results revealed that bacterial community Shannon diversity and Pielou's evenness were highest in TK. The rare taxa were ubiquitous in all soil samples, while the higher Shannon diversity of the abundant taxa of TK may be related to the habitat preferences of species and niche differentiation. The community composition of bacterial and fungal sub-communities exhibited significant dissimilarity between TK and KL. The redundancy analysis further demonstrated that abundant taxa were environmentally more constrained than rare taxa. The bacterial and fungal networks of KL were more complex than TK. The keystones of the network transforms may suggest their significant role in the ecological function of the karst tiankeng ecosystem. This study represents the first reports of the characteristics of bacterial and fungal communities in karst tiankeng.

Comparison of soil microbial community structure and function for karst tiankeng with different degrees of degradation

Karst tiankengs are oases in degraded karst landscapes and act as repositories for biodiversity conservation; however, knowledge about the bacterial and fungal structure and function of the karst tiankeng ecosystems is limited. This study investigated the microbial communities in three different tiankeng (nondegraded, moderately degraded, and heavily degraded tiankeng) by Illumina NovaSeq sequencing. We found that the degradation of karst tiankeng can lead to changes in microbial community structure and functions, while there are differences in bacterial and fungal responses. There were significant differences in bacterial and fungal community composition and beta diversity in the three tiankeng soils. Random molecular ecological network analysis results indicated that a more complex and stable bacterial network existed in nondegraded tiankeng, while more complex fungal networks existed in moderately degraded tiankeng. The keystones of Proteobacteria, Actinobacteria, Acidobacteria, Ascomycota, and Basidiomycota played essential roles in maintaining soil function and stability. The functional profiles revealed that tiankeng habitat changes may affect microbial survival strategies, such as increasing gene abundance associated with the carbon cycle. To our knowledge, this is the first report on bacterial and fungal communities in different degrees of karst tiankeng, which provides crucial insights into our understanding of the microbial communities' structure and potential function in karst tiankeng ecosystems.

Species Diversity of Cordyceps-Like Fungi in the Tiankeng Karst Region of China

Tiankeng acts as a refugium for biodiversity amid a changing global climate, and a previous study has shown that some ancient (Alsophila spinulosa) and unique plants (cool-adapted plants) are present in Tiankeng. However, there are few reports on Ascomycota from the Tiankeng karst region. In this research, the species diversity of Cordyceps-like fungi in Monkey-Ear Tiankeng was investigated. Seven species in the genera Akanthomyces, Beauveria, Cordyceps, and Samsoniella were identified based on internal transcribed spacer sequences and morphological characteristics. Eight new species in the genera Akanthomyces, Cordyceps, and Samsoniella were established and described according to a multilocus phylogenetic analysis and morphological characteristics. Our results revealed that Cordyceps-like fungi were abundant in Monkey-Ear Tiankeng, providing new insights into the diversity of Ascomycota in this special eco-environment. IMPORTANCE Karst Tiankeng has a special eco-environment and acts as a refugium for biodiversity. However, there are few reports on Ascomycota from the Tiankeng karst region. In this research, seven known species and eight new species in the genera Akanthomyces, Beauveria, Cordyceps, and Samsoniella were reported. The results showed that Cordyceps-like fungi are abundant in Monkey-Ear Tiankeng. Interestingly, the month of the sampling was November, which is not an active period of growth and reproduction for Cordyceps-like fungi. These results revealed that unconventional time sampling should not be ignored, especially for a special eco-environment, and provided new insights into the diversity of Ascomycota in this special eco-environment.

The characterization of microbial communities and associations in karst tiankeng

The karst tiankeng is a special and grand negative terrain on the surface, that maintains a unique ecosystem. However, knowledge about bacterial and fungal communities in karst tiankengs is still limited. Therefore, soil samples from five karst tiankengs were collected and subjected to high-throughput sequencing of 16S rRNA and ITS genes, and multivariate statistical analysis. The results showed abundant and diversified bacterial and fungal communities in karst tiankeng. The bacterial communities were dominated by Proteobacteria and Acidobacteria, and the fungal communities were dominated by Ascomycota and Basidiomycota. Statistical analysis revealed significant differences in bacterial and fungal communities among the five karst tiankengs, which may indicate that the distribution of bacterial and fungal communities was driven by separate karst tiankengs. The co-occurrence network structure was characterized by highly modularized assembly patterns and more positive interactions. The keystone taxa were mainly involved in nutrient cycling and energy metabolism. The null model analysis results showed that the stochastic process, especially dispersal limitation, tended to be more important in controlling the development of bacterial and fungal communities in karst tiankeng. The bacterial community structure was significantly associated with soil properties (SWC, TN, AN, and BD), while the fungal community structure was significantly associated with soil properties (SWC and TP) and plant diversity. These results can expand our knowledge of the karst tiankeng microbiome.

Slope aspect affects the soil microbial communities in karst tiankeng negative landforms

Background

Karst tiankeng is a large-scale negative surface terrain, and slope aspects affect the soil conditions, vegetation and microbial flora in the tiankeng. However, the influence of the slope aspect on the soil microbial community in tiankeng has not been elucidated.

Methods

In this study, metagenomic sequencing technology was used to analyze the soil microbial community structure and functional potentials on the shady and sunny slopes of karst tiankeng.

Results

The Shannon–Wiener diversity of microbial communities on shady slope (SHS) was significantly higher than that on sunny slope (SUS). Although the composition of dominant phyla on shady slope (SHS) and sunny slope (SUS) was similar, there were significant differences in beta-diversity. The linear discriminate analysis (LDA) results showed that biomarkers mainly belongs to Actinobacteria, Chloroflexi and Proteobacteria. Functional pathways and CAZy (Carbohydrate-Active Enzymes) genes also had a remarkable response to slope aspect change. LEfSe results indicated several biomarker pathways in sunny slope involved in human disease. Moreover, the abundance of CAZy genes was higher in shady slope and had stronger ability in decomposing litter. The microbial communities were mainly correlation with the vegetation characteristics (species richness and coverage) and soil properties (SOC and pH).

Conclusions

These results indicate slope aspect has a pronounced influence on microbial community composition, structure and function at karst tiankeng. In the future, the conservation of karst tiankeng biodiversity should pay more attention to topographical factors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-01986-y.

Metagenomic analysis reveals the different characteristics of microbial communities inside and outside the karst tiankeng

Background

Karst tiankengs serve as a reservoir of biodiversity in the degraded karst landscape areas. However, the microbial diversity of karst tiankengs is poorly understood. Here, we investigated the composition and function of the microbial community in a karst tiankeng.

Results

We found that habitat differences inside and outside the karst tiankeng changed the composition and structure of the soil microbial communities, and the dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria. The Shannon–Wiener diversity of microbial communities inside and outside the tiankeng was significantly different, and it was higher inside the tiankeng (IT). Venn and LEfSe analysis found that the soil microbial communities inside the tiankeng had 640 more endemic species and 39 more biomarker microbial clades than those identified outside of the tiankeng (OT)..Functional prediction indicated that soil microorganisms in outside the tiankeng had a high potential for carbohydrate metabolism, translation and amino acid metabolism. There were biomarker pathways associated with several of human diseases at both IT and OT sites. Except for auxiliary activities (AA), other CAZy classes had higher abundance at IT sites, which can readily convert litter and fix carbon and nitrogen, thereby supporting the development of underground forests. The differences in microbial communities were mainly related to the soil water content and soil total nitrogen.

Conclusions

Our results provide a metagenomic overview of the karst tiankeng system and provide new insights into habitat conservation and biodiversity restoration in the area.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02513-1.

Species Abundance Distributions Patterns between Tiankeng Forests and Nearby Non-Tiankeng Forests in Southwest China

Identifying the species abundance distributions (SADs) in Tiankeng forests is crucial for restoring and managing degraded karst ecosystem, whereas previous studies rarely explored the differences and response of vegetation dynamics to environmental variations. The species composition and SADs of the inner and outer fringe areas of Tiankeng forest and nearby non-Tiankeng forest were compared in Southwest China. Six models were adopted to compare SADs of three habitats. Kolmogrov–Smirnov (K–S) test was selected to compare the discrepancy between the simulated and observed SAD patterns. The Akaike Information Criterion (AIC) test was adopted to compare the models, and the best model was indicated by the lowest AIC value. The results showed that (1) the species dispersal from the inside of Tiankeng forests to the nearby non-Tiankeng forests is limited, while species have unlimited dispersal from nearby non-Tiankeng forests to the inside of Tiankeng forests via the fringe of Tiankeng forests. (2) Species abundance, species rarity, richness, and species accumulation rate in the Tiankeng forests were significant in non-Tiankeng forests (p < 0.05), and most species in inner Tiankeng forests originated from nearby non-Tiankeng forests. (3) Based on the criterion of K-S values, all models have passed the K–S test (p > 0.05), which indicated that niche processes and neutral process worked together in the maintenance of community species diversity, the community in study area is a niche-neutral continuum. (4) Considered the lowest AIC value, the neutral (△mean AIC = 1.3) models performed better than the niche (△mean AIC = 22.7) models and statistical (△mean AIC = 2.7) in the Tiankeng forest, while the statistical models performed better than the niche and neutral models in the non-Tiankeng forests. The results suggested that the main driving force of Tiankeng forests is the neutral process. The negative terrain in Tiankeng restricted the species dispersal due to topographic constraints. However, the species dispersal from the nearby non-Tiankeng forests could promote the species succession in the inner Tiankeng. Therefore, we propose that nearby non-Tiankeng forests should be emphasized for protecting the biodiversity of Tiankeng forests.

Characteristics of the Soil Microbial Communities in Different Slope Positions along an Inverted Stone Slope in a Degraded Karst Tiankeng

Simple Summary

Karst tiankeng is a special and magnificent surface negative terrain with unique scientific value. The underground forests developed on inverted stone slopes in tiankeng are important areas for biodiversity conservation. This research used Illumina high-throughput sequencing technology to determine the soil microbial communities at four sites (at the bottom of the slope (BS), in the middle of the slope (MS), in the upper part of the slope (US), and outside the tiankeng (OT)) along the inverted stone slopes. The microbial communities at different slope positions presented similar compositions but different abundances. The dominant phyla in the inverted stone slope were Proteobacteria, Actinobacteria and Acidobacteria. The microbial community diversity was greater at the US site. The microbial communities with more abundant functional genes involved in C/N cycles were located at the BS site. The distribution of the microbial community was highly correlated with the Total nitrogen and pH. Understanding the soil microbial communities on inverted stone slopes is important for monitoring the ecology of tiankeng and biodiversity value assessments.

Abstract

The underground forests developed on inverted stone slopes in degraded karst tiankengs are important areas for biodiversity conservation, but the microbial community profiles have not been sufficiently characterized. Thus, we investigated the soil microbial communities at four sites (at the bottom of the slope (BS), in the middle of the slope (MS), in the upper part of the slope (US) and outside the tiankeng (OT)) in the Shenxiantang tiankeng. The dominant phyla in the inverted stone slope were Proteobacteria, Actinobacteria, and Acidobacteria, and the relative abundance were different in different slope positions. The Shannon–Wiener diversity index of the microbial community was significantly greater for the US site than for the MS or BS sites. The metabolism functional pathways (including C/N cycle) were more abundant at the BS site. Total nitrogen and pH were the dominant factors in determining the distribution of the microbial community along an inverted stone slope. These results suggest that topographic heterogeneity can influence the variations in the soil microbial structure, diversity, and function in degraded karst tiankengs and emphasized the ecological value of inverted stone slopes within karst tiankengs.

The Biomolecular Spectrum Drives Microbial Biology and Functions in Agri-Food-Environments

Microbial biomolecules have huge commercial and industrial potential. In nature, biological interactions are mostly associated with biochemical and biological diversity, especially with the discovery of associated biomolecules from microbes. Within cellular or subcellular systems, biomolecules signify the actual statuses of the microorganisms. Understanding the biological prospecting of the diverse microbial community and their complexities and communications with the environment forms a vital basis for active, innovative biotechnological breakthroughs. Biochemical diversity rather than the specific chemicals that has the utmost biological importance. The identification and quantification of the comprehensive biochemical diversity of the microbial molecules, which generally consequences in a diversity of biological functions, has significant biotechnological potential. Beneficial microbes and their biomolecules of interest can assist as potential constituents for the wide-range of natural product-based preparations and formulations currently being developed on an industrial scale. The understanding of the production methods and functions of these biomolecules will contribute to valorisation of agriculture, food bioprocessing and biopharma, and prevent human diseases related to the environment.