The Response of Soil Organic Carbon to Climate Change and Potential to Increase Carbon Sequestration in Soils through Management

Abstract

As the largest terrestrial carbon pool, changes in soil carbon pools in response to climate change or management practices have the potential to significantly impact atmospheric CO2 concentrations. This dissertation examines the effects of climate change and two management strategies on soil carbon pools in order to understand how soil carbon storage might change under these conditions. Changes in soil carbon concentrations were studied in a Danish heath/grassland exposed to elevated CO2, summer drought, and warming. Soil carbon was observed to increase significantly over the course of 8 years in the presence of elevated CO2, regardless of the addition of warming or drought treatments. Soil carbon pools at this site are therefore likely to serve as a negative feedback to increasing atmospheric CO2 concentrations. To examine how management strategies could take advantage of the potential for soils to be used as a carbon sequestration tool, this dissertation also investigated the effects of two types of management practices on soil carbon dynamics. In a Pacific Northwest Douglas-fir stand, deep soil carbon storage was shown to increase when competing vegetation was not controlled, presumably due to deeper Douglas-fir rooting in response to competition for more shallow soil moisture reserves. In an incubation study, applying olivine with the goal of increasing soil pH and capturing CO2 resulted in decreased decomposition of organic matter compared to the application of agricultural lime. There was no difference in CO2 flux between the olivine amended and control samples, whereas the CO2 flux from the limed samples was 221% higher than the control. The application of olivine also increased soil pH to a level sufficient to overcome aluminum toxicity. The use of olivine as an alternative to lime would therefore significantly reduce agricultural CO2 emissions. The results of this dissertation suggest that not only is there potential for increasing soil carbon stocks to serve as a negative feedback to rising atmospheric CO2 concentrations, but that an opportunity also exists to design management practices that utilize soils as a climate change mitigation tool.