The relationships of present vegetation, bacteria, and soil properties with soil organic matter characteristics in moist acidic tundra in Alaska

Abstract

Soil organic matter (SOM) is related to vegetation, soil bacteria, and soil properties; however, not many studies link all these parameters simultaneously, particularly in tundra ecosystems vulnerable to climate change. Our aim was to describe the relationships between vegetation, bacteria, soil properties, and SOM composition in moist acidic tundra by integrating physical, chemical, and molecular methods. A total of 70 soil samples were collected at two different depths from 36 spots systematically arranged over an area of about 300 m × 50 m. Pyrolysis-gas chromatography/mass spectrometry and pyrosequencing of the 16S rRNA gene were used to identify the molecular compositions of the SOM and bacterial community, respectively. Vegetation and soil physicochemical properties were also measured. The sampling sites were grouped into three, based on their SOM compositions: Sphagnum moss-derived SOM, lipid-rich materials, and aromatic-rich materials. Our results show that SOM composition is spatially structured and linked to microtopography; however, the vegetation, soil properties, and bacterial community composition did not show overall spatial structuring. Simultaneously, soil properties and bacterial community composition were the main factors explaining SOM compositional variation, while vegetation had a residual effect. Verrucomicrobia and Acidobacteria were related to polysaccharides, and Chloroflexi was linked to aromatic compounds. These relationships were consistent across different hierarchical levels. Our results suggest that SOM composition at a local scale is closely linked with soil factors and the bacterial community. Comprehensive observation of ecosystem components is recommended to understand the in-situ function of bacteria and the fate of SOM in the moist acidic tundra.