Arctic microbial systems continue to get attention today as our understanding regarding their structure and function in a rapidly changing system is paramount to C feedbacks with warming and changes in precipitation. Since environmental conditions and plant community structure drive microbial cycling of soil organic matter resolving the linkages between environmental drivers, plant communities and microbial community processes across the Arctic landscape is central to understanding tundra ecosystem processes. Here, we want to understand how soil microbial respiration, mineralization, biomass and community composition are linked to three Alaskan tundra plant communities, namely Shrub, Tussock and Sedge tundra. A total of 64 points were visited between 2018 and 2019 within a spatial extent of ca. 44,800 km2. Soils were collected in March, June, July and September, homogenized and incubated at realistic field temperatures to quantify soil microbial respiration (SMR) and potential N mineralization. Microbial C and N biomass were assessed through fumigation/extraction. PLFA extraction was used to assess microbial community structure (nmol/g) from major groups such as Gram+ and Gram- bacteria, Actinomycetes, and Fungi. Soil temperature, water content, thaw depth and pH were collected from all sites in summer. In winter snow depth, snow and snow ground interface temperatures were also measured.
Results/Conclusions
We found significant variation in microbial function across time and among plant communities. In March SMR rates were low but distinct in all plant communities, and allover N mineralization rates were the highest. In July SMR peaked for all plant communities, and for all but Tussock soil N immobilization rates peaked. Although soil microbial activity was high, overall microbial biomass as measured MBC, MBN and PLFA (nmol/g) was at the lowest point in July. These results show the strong influence of seasonality where microbes are mineralizing inorganic N during the winter and immobilizing inorganic N during growing season. Summer is the time when microbial- plant interactions are most pronounced and stresses the importance of winter for annual C and N cycling in the Arctic. No significant differences between soil microbial community structure among the different plant communities was found which suggests that a potential plant driven change in microbial function is not changing community-level microbial structure.