Investigating soil dissolved organic matter composition to inform its fate in furture warmer and wetter boreal forests

Boreal forests store large amounts of soil organic carbon (SOC) yet rising temperatures and intensified precipitation due to climate change are increasing the vulnerability of these stocks. The movement of dissolved organic matter (DOM) is a primary pathway of carbon transfer to and from mineral soils; however, current carbon budget models do not account for carbon storage and loss via DOM transfer, despite the evidence of increased DOM mobilization under warmer and wetter conditions. Improving the accuracy of global carbon models requires a clearer understanding of the processes associated with DOM retention and release in boreal forest mineral soils. This thesis describes experimental investigations of: (1) how two main soil processes, microbial degradation and mineral soil physicochemical processes, alter DOM composition, and (2) how initial soil moisture and soil carbon saturation impact the composition of DOM retained or released by mineral soils over event-based time scales (days-weeks). This study demonstrated that coupled monitoring of soil DOM aromaticity and amino acid composition described the degree and type of transformation DOM undergoes on an event-based timescale. Monitoring these characteristics can provide insight into the fate of DOM and mineral SOC stores with increasing climate change.