Past decomposition dynamics in Arctic terrestrial environments revealed by shotgun sedaDNA

Dynamics of litter decomposition in Arctic terrestrial environments control about carbon storage in permafrost soils and release of CO₂ into the atmosphere. Climate warming can accelerate litter decomposition because degradational processes increase, due to shifts in types of labile organic matter available and the composition of decomposing taxa. How litter decomposition changed in former interglacial and glacial periods is rarely studied, because time-series data is lacking, but highly needed to foresee consequences of decomposition and carbon cycling for warming Arctic ecosystems. Innovative shotgun ancient DNA sequencing on sediment core samples provide a snapshot of entire components of past biotic ecosystems and deliver qualitative data on organismal and functional compositional shifts. Our study, for the first time, investigates sedimentary ancient DNA shotgun data in a 52ka sediment core from Far North-Eastern Russia, Lake Ilirney, that recovers former glacial and interglacial periods with pronounced shifts in taxonomic composition in terrestrial vegetation, microbial and fungal diversity. At the same time, the ancient DNA data provides information on gene functions, like degrading enzymes that support variation in functional composition through time. With this data, we aim to understand how litter quality, based on vegetational composition, alters the taxonomic (bacteria, fungi) and functional (enzymes involved in decomposition) community of decomposers. Our result show that glacial times are characterized by tundra vegetation, mainly herbs, accompanied with a dominance of cryophilic soil degraders and relatively lower abundance of enzymes degrading plant organic material. Interglacial periods (like late Holocene) are typified by shrub-tree and heath dominated vegetation with microbes more specialized to degrade plant material, which is supported by an increase of the relative abundance of cellulose and ligninolytic enzymes. Our preliminary results support that under future warming the expansion of shrubs and trees and the increase of specified degraders in Arctic terrestrial environments might lead to enhanced degradation of plant litter resulting in a potential increase of CO₂ emissions.