Using Novel Metabolomics Approaches to Understand Microbial Carbon Cycling in Response to Precipitation in Desert and Grassland Soils.

The cycling of soil organic matter (SOM) by microorganisms is a critical component of Earth’s carbon cycle but remains poorly understood. Of vital importance is how the distribution of carbon between the atmosphere and the subsurface will change in response to altered rainfall, temperature and vegetation patterns. In this project, we investigate how altered rainfall impacts the dynamics of carbon stored in desert and grassland soils using experimental manipulation of water inputs to mimic shifting precipitation regimes that are relevant to climate change scenarios. Here we establish a simple soil extraction and metabolomics workflow that will enable rapid comparison between samples collected at various timepoints during rainfall manipulation and at different depths.

To release metabolites from microorganisms and obtain a measurement of total extractable organic matter (intracellular and extracellular), soil was fumigated with chloroform vapor while unfumigated soil was used as a measure of extracellular compounds. A series of extractants were tested (aqueous vs. organic solvents) and extracts analyzed by gas chromatography/ mass spectrometry.  In total, 55 metabolites were identified, with fumigation having a significant effect on the range and intensity of metabolites. Sugars (fructose, glucose, trehalose, sucrose) were among the most abundant, followed by sugar alcohols, fatty acids, dicarboxylic acids, sterols, nucleobases, osmolytes and many other metabolic intermediates. Water was one of the most effective extractants in terms of the number and range of metabolites detected. The inclusion of organic solvent facilitated the extraction of fatty acids and sterols. This study presents a simple SOM extraction and metabolomics workflow that will be combined with genomics, proteomics and transcriptomics to understand how desert and grassland ecosystems will respond to future climate change.