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On Wednesday 1 April, Songyu Yang will defend his PhD thesis

Detail Summary
Date 1 April 2020
Time 10:00

As long as the measures related to the coronavirus remain in force at the UvA, PhD defence ceremonies will take place online (using Zoom) rather than on location in the Aula or the Agnietenkapel. 


Soil organic matter in the Peruvian Andes - Unravelling factors controlling soil organic carbon distribution and the underlying organic matter stabilization mechanisms

Alpine grasslands of the Peruvian Andes are characterized by large soil organic carbon (SOC) stocks. The large SOC stocks are crucial to the ecosystem services but less-studied with regard to their persistence and the underlying mechanisms. The objectives of this thesis were to quantify the SOC stocks and find key factors controlling the SOC spatial distribution, and to gain insights into the underlying mechanisms of organic matter (OM) stabilization. Soil samples were collected from sampling sites with contrasting lithologies (limestone and acid soils) and precipitation levels (wet and dry sites). For the wet site, lithology was the key factor controlling SOC spatial distribution. Limestone soils had higher SOC stocks, which can be explained by the OM stabilization controlled by Ca2+ bridges in addition to the Fe- and Al-controlled stabilization that was found in all soils. In both wet and dry sites, OM stabilization was mainly controlled by adsorption on mineral surfaces, whereas occlusion in aggregates played a minor role. SOC stability estimated by SOC mineralization rates decreased with precipitation in limestone soils but had limited changes in acid soils. The SOC mineralization rates were predicted by relative abundances of unsaturated fatty acids, whereas the stability of fatty acids was controlled by the presence of double bonds and carbon chain length, likely through their interactions with the soil matrix. The results highlight that the SOC stability is controlled by interactions between precipitation and soil mineralogy, whereas the inherent properties of OM also affect its persistence and interactions with the soil matrix.