Soil organic carbon stabilisation in summer grazed low-alpine podzols

This study aims to improve mechanistic understanding of SOM stabilisation through analysis of three Podzols subjected to varying summer grazing intensity in Setesdal, Norway. Setesdal is a low-alpine region with high precipitation, low temperatures and nutrient poor, coarse soils of intrinsically high soil organic matter (SOM) content. Combined with a long sheep grazing history and its stimulation of particulate organic matter (POM) forming low-quality litter, these pedoclimatic conditions produce remarkable characteristics, such as millennia-old POM. The contribution of inherent properties versus external climatic factors in controlling SOM stability in these systems remains unclear.

The profiles were sampled along a natural sheep density gradient derived from local practices, with one sample from each soil horizon, totalling fifteen, being analysed; SOM fractions are currently being analysed for composition (FTIR spectroscopy), thermal stability and radiocarbon age (TGMS and ramped combustion radiocarbon dating). We hypothesise that highest SOC stocks will be found under highest grazing pressure. We also hypothesise that SOC persistence is primarily controlled by external factors rather than mineral association, with some complex POM compounds providing intrinsic decomposition resistance, and that POM dominates carbon persistence in O- and E horizons, while mineral associated organic matter (MAOM) dominates in B horizons. Preliminary findings suggest a decoupling between SOM stabilisation and turnover times, implying that POM plays a larger role in long-term carbon storage in low-alpine systems than previously recognised. Using novel thermal techniques, our study offers insights into SOM stability and dynamics in cold, wet regions.