The relative contribution of the five pedogenesis factors to soil formation and soil organic matter incorporation across environmental gradients

Climate change is likely to call into question the future persistence of soil organic carbon (SOC) in terrestrial ecosystems. Given the complexity of soil organic carbon evolution, plant-soil interactions, climatic conditions and biotic factors are key to understanding ecosystem functioning and soil formation. In recent decades, human-induced climate change, habitat destruction and ecological disturbance have led to significant changes in socio-environmental dynamics, resulting in altered soil properties and ecosystem dynamics. These changes are expected to have a major impact on the services that soils provide to man, threatening the persistence of many species and, consequently, the overall health of ecosystems. Studying SOC changes in a changing world is crucial for understanding contemporary environmental systems. In this thesis, I first sought to understand how environmental changes drive SOC changes in soils over decades, examining soils from the perspective of an environmental gradient, from lakeshores to alpine meadows. Secondly, I studied how changing environmental conditions - using altitude gradients - drive organic matter decomposition dynamics in the context of climate change. Decomposition dynamics are not only influenced by global warming; they are also expected to change with altitude, as vegetation cover shifts and migrates upwards to follow optimal temperatures under warming.

I therefore use altitude with north- and south-facing slopes in the Swiss Alps to simulate future climate scenarios. The study of soils across time and environmental gradient to predict SOC change is presented in themes 1 and 2. The study of decomposition dynamics using altitude gradients for climatic variation as well as north-south oriented slopes and teabags is presented in themes 3 and 4. Furthermore, to further investigate the effect of plant organ pytochemistry on decomposition dynamics, I used handmade litter bags filled with local plant material to show how leaf and root phytochemistry influences litter decomposition in a litter transplant experiment (theme 3). Last but not least, to examine the last soil-forming factor, I also studied microarthropod diversity along altitude gradients to better explain local ecological indicators of soil biodiversity (theme 4).