Conservation of fragile karst forests through rhizosphere microbiome of endangered species and ecological restoration of Hopea celebica

Abstract

BACKGROUND AND OBJECTIVES: Hopea celebica is an endangered dipterocarp endemic to Sulawesi, restricted to fragile karst forests with shallow nutrient- poor soils. Furthermore, the conservation value is high, yet the threats to its habitat are on the rise, and ecological knowledge, especially concerning its belowground microbial relationships, is still quite restricted. The rhizosphere microbiome plays an important role in plant nutrition and stress tolerance, yet the microbial community associated with H. celebica remains undocumented. The objective of this study was to record the diversity of bacteria and to identify the ecologically and functionally significant dominant taxa in the rhizosphere of H. celebica in the Maros-Pangkep Karst region.METHODS: Rhizosphere soil samples were collected from four natural populations of H. celebica within the Maros Karst region, South Sulawesi, Indonesia. Total community deoxyribonucleic acid was extracted, and the composition of the bacterial community was analyzed using 16S ribosomal ribonucleic acid gene amplicon sequencing targeting the Variable regions 3 and 4 region on the deoxyribonucleic acid nanoball sequencing-G400 platform. Sequence data were processed using the quantitative Insights Into microbial ecology 2 pipeline, including quality filtering, amplicon sequence variant inference, and taxonomic classification against the systematic interactive labeled viewer of alignments 138.1 reference database. Alpha diversity indices were applied to evaluate bacterial richness and evenness among sampling sites.FINDINGS: A total of 89,862 high-quality sequence reads were obtained, representing 12 bacterial phyla, 103 orders, 155 families, 204 genera, and 720 species. Proteobacteria were the most abundant and diverse phylum, forming two major phylogenetic clusters dominated by families such as Geminicoccaceae, Methyloligellaceae, and Rhizobiales incertae sedis. The family Gaiellaceae, especially the Gaiella genus, consistently exhibited dominance across every sampling sites. The analysis of alpha diversity revealed that the composite sample derived from rhizosphere soils linked to mature trees at the Leang-Leang site exhibited the highest bacterial richness and community evenness when compared to the other samples tested..CONCLUSION: As an initial exploratory baseline, this study reveals that Hopea celebica is associated with a structured rhizosphere microbiome functionally equipped for extreme environments. The prominence of particular taxa implies possible essential functional roles, including the solubilization of rock phosphates, the promotion of nitrogen cycling, and the enhancement of stress tolerance, which collectively aid in the survival of plants in nutrient-scarce karst soils.

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