ABSTRACT                              

Microbiota are pivotal to the ecological and biogeochemical processes of deep-sea wood-fall ecosystems. However, the dynamics and interactions of archaea within these ecosystems remain poorly understood. This study determined the age and source of a deep-sea wood fall in the South China Sea (SCS) and investigated the diversity, community assembly, and ecological functions of archaeal microbiota via 16S rRNA gene amplicon sequencing. The results showed that the deep-sea wood fall was identified as Homalium hainanense Gagnep., with associations to wooden vessels from the 1979-1981 period onwards. The center of taxonomic and functional diversity of the archaeal microbiota is located in the transition region (TR) of the deep-sea wood fall. Compared to the sediment contact surface (SDCS) and seawater contact surface (SWCS), the archaeal ecological interaction network (AEIN) in TR exhibits higher net immigration rates, as well as resilience and energy-information efficiency. Archaeal community assembly in deep-sea wood fall is dominated by stochastic processes, which account for over 90% of assembly processes across all contact surfaces. The ecological functions of the archaeal community in TR are co-dominated by methane metabolism (65.7%) and nitrogen metabolism (34.3%), whereas those in SDCS and SWCS show pronounced enrichment in methane metabolism (97.6%) and nitrogen metabolism (100%), respectively. The archaeal diversity and interaction hub may serve as an indicator of the fastestdegrading zone in deep-sea wood fall. The TR may also provide diverse ecological niches that maintain this inherently unstable archaeal community. In addition, the prevalence of stochastic processes likely plays a crucial role in maintaining archaeal diversity. Furthermore, the archaeal community is critical to carbon, hydrogen, and nitrogen cycles within the deep-sea wood fall: methane metabolism is active in the archaeal community during the early and middle stages of wood-fall degradation, whereas nitrogen metabolism dominates the community's biogeochemical activities in the late stage. These findings provide new insights into the age and source of deepsea wood falls in the SCS, and highlight the diversity, ecological functions, and biogeochemical processes of archaeal microbiota in deep-sea wood-fall ecosystems.