Abstract

ABSTRACTThe geological role of microorganisms has been widely studied in the karst cave ecosystem. However, microbial interactions and ecological functions in such a dark, humid, and oligotrophic habitat have received far less attention, which is crucial to understanding cave biogeochemistry. Herein, microorganisms from weathered rock and sediment along the Heshang Cave depth were analyzed by random matrix theory-based network and Tax4Fun functional prediction. The results showed that although the cave microbial communities have spatial heterogeneity, differential habitats drove the community structure and diversity. Actinobacteria were predominant in weathered rock, whereas Proteobacteria dominated the sediment. The sediment communities presented significantly higher alpha diversities due to the relatively abundant nutrition from the outside by the intermittent stream. Consistently, microbial interactions in sediment were more complex, as visualized by more nodes and links. The abundant taxa presented more positive correlations with other community members in both of the two networks, indicating that they relied on promotion effects to adapt to the extreme environment. The keystones in weathered rock were mainly involved in the biodegradation of organic compounds, whereas the keystone Nitrospira in sediment contributed to carbon/nitrogen fixation. Collectively, these findings suggest that microbial interactions may lead to distinct taxonomic and functional communities in weathered rock and sediment in the subsurface Heshang Cave.IMPORTANCE In general, the constant physicochemical conditions and limited nutrient sources over long periods in the subsurface support a stable ecosystem in karst cave. Previous studies on cave microbial ecology were mostly focused on community composition, diversity, and the relationship with local environmental factors. There are still many unknowns about the microbial interactions and functions in such a dark environment with little human interference. Two representative habitats, including weathered rock and sediment in Heshang Cave, were selected to give an integrated insight into microbial interactions and potential functions. The cooccurrence network, especially the subnetwork, was used to characterize the cave microbial interactions in detail. We demonstrated that abundant taxa primarily relied on promotion effects rather than inhibition effects to survive in Heshang Cave. Keystone species may play important metabolic roles in sustaining ecological functions. Our study provides improved understanding of microbial interaction patterns and community ecological functions in the karst cave ecosystem.

Highlights

  • The geological role of microorganisms has been widely studied in the karst cave ecosystem

  • A response ratio analysis of the top 12 phyla (97.80%) was conducted, showing that Actinobacteria was more abundant in weathered rock, whereas Proteobacteria, Acidobacteria, Chloroflexi, Planctomycetes, Nitrospirae, Candidate, and Thermotogae were more abundant in sediment (Fig. 1a)

  • As to the top 16 genera (50.30%), the relative abundances of Crossiella, Sphaerobacter, Solirubrobacter, and Rubrobacter were higher in weathered rock, while the relative abundances of Brevitalea, Gemmatimonas, Planctomycete, Nitrospira, Bacterium, Gaiella, and Anaerolinea were higher in sediment (Fig. 1b)

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Summary

Introduction

The geological role of microorganisms has been widely studied in the karst cave ecosystem. The keystones in weathered rock were mainly involved in the biodegradation of organic compounds, whereas the keystone Nitrospira in sediment contributed to carbon/nitrogen fixation These findings suggest that microbial interactions may lead to distinct taxonomic and functional communities in weathered rock and sediment in the subsurface Heshang Cave. Two representative habitats, including weathered rock and sediment in Heshang Cave, were selected to give an integrated insight into microbial interactions and potential functions. Our study provides improved understanding of microbial interaction patterns and community ecological functions in the karst cave ecosystem. It has been proposed that cave microorganisms were translocated soil heterotrophs, which were transferred into the cave by air currents or water percolating from the terrestrial surface [5] These exotic microorganisms were subsequently adapted to different habitats in caves, such as weathered rock, sediment, stalagmite, and drip water [6, 7]. Our understanding about the microbial interactions in the shallow subsurface of karst caves is still very limited

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