To achieve the above objectives, the participant has split the project into four work packages with each having a six-month period. The structure and relationship among these WPs see Fig. 1. The main tasks included the preparation of expedition for new sample collection, development of new method of metabolic flux analysis, incubation of soil and marine sediment with 13C glucose addition, analysis of microbial lipids and their carbon isotope composition, and dissemination of scientific results as well as the following manuscript writing. The preliminary results show:
1: We developed a new approach of lipid-based metabolic flux analysis model on MATLAB platform, which aims to reveal the metabolic C flux pattern for specific/individual group within the microbial community in environmental settings (Objective 1).
2. The further application on soil samples with this model shows a distinct metabolic pattern for Gram-positive vs Gram-negative bacterial groups. The significance of our approach is to provide an experimental evidence of metabolic diversity within the microbial community, supplementing the information of genome-based metabolism information. (Objective 3, 4).
3. To further probe the effect of environmental conditions on the microbial organic matter utilization, we incubated the marine sediments from the Baltic Sea (low-salinity and methanic condition) and Laptev Sea, Arctic Ocean (high salinity and sulphate reduction) with different 13C glucose isotopomers. The preliminary results show a distinct metabolic way in oceanic sediment and terrestrial soil. In detail, soil microbial community prefers to utilize the pentose phosphate pathway to degrade glucose; whereas sedimentary microbes prefer Embden-Meyerhof-Parnas glycolytic pathway. Moreover, sedimentary redox conditions can affect the microbial metabolism with different fluxes through the metabolic network. Our work provides quantitative evidence on the microbial C utilization way, further regulating the biogeochemical C cycle in terrestrial and oceanic environment from the perspective of microbial intercellular activity. (Objective 3, 4, 5)
4. By using the marine sediment from the methane seep area in the outer of Laptev Sea, microbial lipids (e.g. fatty acids and hopenes) and their carbon isotopic compositions suggest a non-active contemporary anaerobic methane oxidization in the upper 20 cm sediment. However, the presence of hopene over upper 20cm sediment suggests an “ancient” aerobic methane microbial community in water column, further imprinting in the archived marine sediments. This work probably indicates that aerobic microbes in water column have an important role of attenuating the methane from the marine sediment in the Laptev Sea, Arctic Ocean. (Objective 2)
5. This project and the preliminary results have been disseminated via the various ways including social media and scientific conferences. It has been publicized on social media such as Facebook, Twitter, Instagram and departmental website after merging with the International Siberian Shelf Study 2020. The participants presented the results on several conferences including European Geosciences Union General Assembly, Bolin Day and ACES Day in 2021. The dissemination of this project aims to advancing the public attention on the global change in Arctic C cycling. (Objective 5)
