Soil organic matter characteristics in moist acidic tundra and its relationship with vegetation, soil bacteria, environment, and microtopography

Abstract:

Soil organic matter (SOM) in the Arctic tundra region contains a huge amount of carbon (C) which is susceptible to climate change. Understanding the quality as well as the quantity of SOM is essential to predict the C dynamics in terrestrial ecosystem that is undergoing climate change. Therefore, we investigated the molecular compositions of SOM and the relationships between SOM chemistry with both plant and soil properties in a moist acidic tussock tundra found in Council, Alaska. A total of 70 soil samples was collected at two different depths with 10 cm intervals from 36 spots arranged with 25 m spaces over an area of about 300 m 50 m. Pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) and pyrosequencing of 16S rRNA gene were used to identify the molecular composition of SOM and bacterial community, respectively. Soil physico-chemical properties were also measured. Our results showed that SOM composition was spatially structured and linked to microtopography however, vegetation, soil properties, and bacterial community composition did not show any spatial structure in overall. The composition of SOM was clearly descried by three different groups: Sphagnum moss-derived SOM, lipids and lignins rich materials, and aromatic rich materials. Simultaneously, soil properties and bacterial compositions were main responsible of variation for SOM composition, while vegetation composition had a residual effect. While Sphagnum moss-derived SOM was associated with higher soil MC and lower soil pH, aromatic rich materials were related to the lower TC content. Our study demonstrates that SOM composition in the moist acidic tundra was strongly related to soil properties and bacterial community composition rather than current vegetation structure.