Carbon Productivity of Plant Communities and Soils, Cryogenic Processes, and Microbiological Activity in Southern Hypoarctic Tundra Landscapes of the Yana-Indigirka Lowland, Russia

To assess the carbon productivity of plant communities, soils, and the heterotrophic res-piration of permafrost landscapes, we conducted studies in the southern hypoarctic shrub tussock tundras of northeastern Siberia. We determined the structural characteristics, quantified the above-ground and below-ground phytomass, and evaluated the carbon and nitrogen deposition by various community components, plant fractions and organs. Our findings establish that the most significant primary producers in the southern tundras are deciduous shrubs, bryophytes, and graminoids. The degree of mortmass accumulation indicates a significant slowdown in the microbial decomposition of plant residues and a low rate of annual production. Shrub-lichen-green moss tundras with a significant pres-ence of Eriophorum vaginatum L. in the ground cover accumulate the most total organic carbon (TOC) in the litter-humus and peat layer—449.48 t C ha-1, which is double that of shrub-sphagnum-green moss tundras with Carex L. species. In the mineral layer at 0–10 cm depth, the corresponding values are 29.47 and 6.07 t C ha-1. With continued climate warming, large-scale thermokarst development, an increase in the proportion of grass-sedge bogs, and a reduction in shrub community area could lead to a net carbon loss from the southern hypoarctic tundras. Microbiological parameters showed that the shrub-lichen-green moss tundra has a stable microbial community with high respiratory activity in the litter-humus (23.745 µg CO2-C/g soil/hour) and peat layers (70.627 µg C/g soil), as well as high availability of TOC for processing. The microbial metabolic quotient ranged from 0.14 to 0.73.