Network analysis of integrated mass spectrometry and genetic data provides new insights on microbial carbohydrate and lignin transformations resulting from long-term experimental warming.

Abstract:

Complex interactions between members of the soil food web including plants, insects, fungi, bacteria and viruses determine soil carbon dynamics and other soil biogeochemical transformations. In our long-term soil warming experiment in the Barre Woods tract at Harvard Forest, a 5C elevation in soil temperature has increased respiration rates and resulted in a net loss of soil carbon and increase nitrogen mineralization. In order to link microbial metabolism with soil biogeochemistry, we measured cellular metabolism and soil organic matter chemistry using both next generation sequencing and high-resolution mass spectrometry (MS). The high resolving power and measurement accuracy of masses detected with FTICR-MS of soil organic matter enabled us to identify 16,814 carbon molecules, including 57.8% with assigned molecular formula and 15.2% with hits to the KEGG database. Changes associated to lignin, hydrocarbons, and lipids reveal significant differences with the warming treatment. Microbial diversity also shows shifts in response to the temperature treatment, including metabolic changes associated to degradation of benzoic compounds, denitrification and ammonification, sulfur assimilation, and potassium uptake. Other metabolic changes associated with cellular processes such as dormancy and sporulation also increased with the experimental treatment. Targeted analysis of cellular metabolites (GC-MS) and lipids (LC-MS/MS) revealed differential abundant metabolites, including a potent inducer of cellulases. Network analysis integrated both MS and metatranscriptomes providing new insights on microbial carbon transformations. This integrative approach provides a framework to inform soil respiration models that can be incorporated into ecosystem and biogeochemical processes.