Effect of nitrogen availability on lignin stability in soils

This PhD project aims to explore the biotic and abiotic mechanisms of the interactions between reactive nitrogen species and key compounds of soil organic matter (SOM), such as lignin, and their impact on soil N availability, soil organic matter stability and soil N trace gas emissions. The project has two main objectives:
1. To elucidate the mechanisms of nitrogen immobilization/fixation by SOM key compounds and their impact on N turnover, soil-atmosphere N exchange, N leaching, N fixation by SOM and microbial N immobilization;
2. To analyze the effect of N availability on lignin stability and decomposability. The research will focus on changes of extracellular oxygenase activities (LiP, MnP and Lac), shifts of lignin-degrading microbial communities (abundances and activities), as well as the pathways of lignin decomposition (metabolites, turnover rate and accumulation in SOM).
Incubations (e.g. litter-bag method) will be set up to mimic the natural conditions in organic and mineral layers of forest, grassland and agricultural soils as closely as possible with respect to in situ concentrations of ammonium, nitrate and organic substrates. Stable isotope tracing will be applied to detect the fate of N and the SOM key compounds.