Influence of elevated carbon dioxide (eCO2) on microbial communities linked to carbon cycling in mangrove sediments

Abstract

The rapid growth in global population has led to excessive energy consumption, resulting in elevated carbon dioxide (eCO2) levels and dramatic climate change effects. As a mitigation strategy, considerable attention has turned to carbon sequestration in various ecosystems. One global hotspot for carbon sequestration is the mangrove ecosystem, which excels in capturing and storing large amounts of carbon, particularly in their sediments. Besides providing crucial ecosystem, mangrove sediments support diverse microbial communities essential for carbon cycling and maintaining the ecosystem’s high carbon sequestration capacity. Despite their recognised carbon sequestration potential, the impact of eCO2 on microbial communities in mangrove sediments remains underexplored. This thesis investigates how eCO2 levels affect changes in the composition and function of microbial communities linked to carbon cycling in mangrove sediments. Mangrove sediments of different depths were collected from Kuala Selangor Nature Park and subjected to aerobic and anaerobic enrichments of CO2 (278,000 ppm) over 72 hours of incubation. Physicochemical analyses, including pH, salinity, particle size, and organic matter content, were also determined. At selected time points (0, 4, 8, 12, 24, 48, 72 h), the headspace and sediments were collected to determine the CO2 concentration and to analyse the microbial community and functional changes using 16S rRNA amplicon sequencing. The physicochemical results revealed variations in soil properties across depths and differences in organic carbon decomposition rates under aerobic and anaerobic conditions. Taxonomic analyses of the V3-V4 region of the 16S rRNA gene revealed a diverse range of bacterial taxa, with key species such as Catenococcus thiocycli, Vibrio chemaguriensis, and Methyloceanibacter caenitepidi playing crucial roles in sulfur oxidation, organic matter decomposition, and methanogenesis, respectively. These taxa exhibited shifts in relative abundance over time in response to eCO2 levels. Despite the changing microbial composition, functional predictions indicated consistent carbon-related microbial activities, highlighting the resilience of microbial communities in carbon cycling processes. This study provides fundamental insights into microbial adaptation to elevated CO2 and its implications for carbon regulation in mangrove sediments.