Landscape and environmental controls on soil organic matter decomposability in the High Arctic

Abstract

I employed 90 day-laboratory soil incubations, proximate carbon fraction analysis, diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to explore how variability in vegetation and soil moisture across the High Arctic landscape influences soil organic carbon (SOC). My results demonstrate that vegetation type significantly influences the size of labile and more persistent SOC pools and labile SOC mineralisation rates in the High Arctic. Wet sedge (WS) soils had significantly higher SOC decomposability than mesic tundra (MT) and polar desert (PD) soils. Further evaluation of soils under dominant High Arctic plant types: Salix arctica Pall (SA), bare ground mats (BGM) and moss identified as Grimmia torquata Drumm. (GT) reveal that plant type significantly influences more persistent SOC mineralisation rates. Spectroscopy results (from NEXFAS) corroborated incubation results, revealing significantly lower alkyl/O-alkyl ratios in BGM than GT (p<0.001) and SA (p=0.002). Similarly, proximate C fraction analyses of plant tissue samples found higher lignin content in SA roots, litter, and stems than BGM, fresh SA leaves and GT plants. Stronger correlation between plant tissue and soil lignin was observed in lower depths than in surface depths of soil underlying all plant types. Finally, the research investigated the influence of moisture controls on SOC decomposability and found that moist wet sedge (MWS) had significantly higher alkyl/O-alkyl ratios and molecular diversity than dry wet sedge (DWS). Positive correlation was observed between field moisture and CO2 production (mg/gC) with field moisture (FM) predicting about 20% of the variation in CO2 production compared to 1.4% predicted by SOC. Similarly, strong positive and significant correlations were observed between field moisture (FM) and SOC content with FM predicting approximately 83% of the variation in SOC in WS soils. Overall, this study establishes that variability in SOM decomposability linked to vegetation and moisture controls can influence rates of release of C to the atmosphere following warming in the High Arctic