Effect of mineral sediments on carbon mineralization, organic matter composition and microbial community dynamics in a mountain peatland
Citation
Wang, X., Helgason, B., Westbrook, C., Bedard-Haughn, A. (2016). Effect of mineral sediments on carbon mineralization, organic matter composition and microbial community dynamics in a mountain peatland. Soil Biology & Biochemistry, [online] 103 16-27. http://dx.doi.org/10.1016/j.soilbio.2016.07.025
Plain language summary
Rocky Mountain peatlands store a vast quantity of carbon. Climate change may result in a loss of this carbon to the atmosphere as carbon dioxide, an important greenhouse gas. Mountain peatlands are formed from decomposing plant material, however not all peatlands are formed under identical conditions and thus do not contain the same forms of peat. For example, there can be layers of mineral soil embedded in the mostly organic peat material. We determined that these embedded mineral soils reduced the proportion of carbon lost from deep in the peat/soil profile compared to fully organic peat. This reduction was attributed to the effect of the mineral soil layer on chemistry of the adjacent peat, the type and abundance of microbial peat decomposers that generate the carbon dioxide and by slowing water infiltration. Our findings show that mineral soil interbedding is an important factor in predicting the response of Rocky Mountain peatlands to climate change.
Abstract
Carbon (C) dynamics in northern peatlands are an important factor in the global C balance under climate change scenarios. They are microbially driven and influenced by the chemical composition of organic matter. Peatlands in the Rocky Mountains are usually formed on mineral sediments or developed with interbedded mineral lenses, which have been found to affect soil properties such as volumetric water content, pH, TOC and TN. Our objective was to investigate whether the presence and relative depth of mineral horizons (i.e., stratified mineral horizons) affect microbial community structure and C composition, and in turn influence C mineralization. Three organic soil profile types were selected in the Sibbald research wetland of southwestern Alberta: peat over silty mineral over calcareous sediment (PMC), peat over silty mineral over peat (PMP), and sedge peat over moss peat profiles (PP). Peat samples were subjected to C composition and microbial community abundance and structure measurement and then incubated to test potential C mineralization. The main differences were detected in subsurface peat. In subsurface peat above mineral sediments (PMC, PMP) versus at equivalent depth in PP, the presence of a mineral horizon caused different C mineralization (mg C-CO2 kg−1 soil) among soil types (PP > PMC and PMP). In addition, specific C mineralization (mg C-CO2 kg−1 SOC) decreased with depth in subsurface peat in PP, but not in PMP, as greater volumetric water content (θv) above the mineral horizon created anaerobic conditions in PMP. Microbial community structures also differed between PMP and PP due to different θv in peat below mineral sediments. Recalcitrant C: labile C, bacteria: fungi, and microbial physiological stress were greatest in the subsurface peat above mineral sediments. Depth had an even greater effect: both C mineralization and microbial abundance decreased significantly with depth. Moreover, microbial community structure mainly grouped according to relative depth. Overall, our findings indicated that stratified mineral horizons affected C mineralization, microbial community structure, and peat chemistry in subsurface peat.