Composition of Dissolved Organic Matter in Arctic Soils

The composition and molecular characteristics of dissolved organic matter (DOM) in arctic soils are largely unknown. We are examining the chemistry of soil DOM as part of a larger effort to understand the biotic and abiotic factors driving the decomposition of organic matter in arctic soils. Current terrestrial carbon models have limited predictive capability for arctic soils partly because they were developed for temperate soils, and partly because they over-simplify the complex nature of soil organic matter. Our research seeks to link the activities of microbes at the molecular level to decomposition processes at the ecosystem scale, and to understand how they may be affected by rapid climate change.

This work focuses on characterizing organic components of soil pore water and in microbial biomass from different vegetation types at Toolik Field Station in northern Alaska. Vegetation types include wet sedge (Carex aquatilis and Eriophorum angustifolium), moist acidic tussock (E. vaginatum) and shrub (Betula nana and Salix sp.) tundra. These sites were sampled during winter/summer transitions in order to capture both growing season and winter dynamics. Soil pore water was isolated through centrifugation and is being characterized through the use of ultra high performance liquid chromatography (UPLC) in line with a quadrupole time of flight mass spectrometer (Q-TOF-MS). Microbial biomass constituents were isolated using chloroform fumigation and are being investigated for composition across seasons and vegetation types to examine physiological adaptations of these microbes to their environment.

We predicted the composition of DOM would differ among vegetation types due to distinct plant inputs and microbial communities, however, initial data from UPLC-MS analysis indicated no difference in wet sedge and tussock tundra soil pore water. Instead, the pore water DOM consisted of a common set of typical fulvic acid-like features along with a suite of approximately 40 small molecules ranging in mass from 191 to 636 amu. Quantification of microbial biomass constituents is ongoing with the expectation that winter sampling will reveal higher concentrations of cryoproctectants such as trehalose. The integration of soil pore water and microbial biomass DOM dynamics across seasons is the starting point for understanding how rapid climate change will affect these pools, and what the consequences of these changes are for ecosystem level carbon cycling.