Research on carbon fixation in the deep sediments of the Challenger Deep(Supplement data)
Nevertheless, it remains unclear how carbon fixation pathways are vertically organized across redox gradients in hadal sediments, which energy conservation mechanisms support autotrophy under extreme energy limitation, and whether hydrogen functions as a primary driver of anaerobic carbon fixation in the deepest sediment layers. To address this knowledge gap, we analyzed the microbial carbon cycle in a 7.5 m sediment core retrieved from the Challenger Deep in the Mariana Trench. Metagenomic sequencing and metagenome-assembled genome (MAG) analysis were used to resolve the vertical stratification of microbial carbon fixation pathways and their coupled energy conservation mechanisms across redox gradients.The objectives of this study were to: (1) characterize the vertical distribution of microbial carbon fixation pathways across redox-stratified hadal sediments; (2) evaluate the dominance of energetically efficient autotrophic pathways under oxygen-depleted conditions; and (3) assess the role of hydrogen as an energy source supporting anaerobic carbon fixation and mixotrophic lifestyles in the deepest sediment layers.