Physical and biological controls on the soil carbon dioxide profile

In this dissertation, I present results from a new automated sampling system designed to measure changes in the soil CO2 profile on an hourly basis, to measure CO2 production with depth over the course of a season at a remote field site, and to identify the contribution of different sources to CO2 production in the soil.; Chapter 1 presents an overview of terrestrial carbon cycling. It also describes how soil CO2 profile measurements can be used to quantify soil CO2 production with depth and how to partition that production between different sources.; Chapter 2 describes the automated sampling system and a laboratory experiment designed to quantify soil CO2 transport using a high CO2 tracer.; Chapter 3 describes the first field test of the automated sampling system, located in a dry marsh soil. The results show that the belowground CO 2 profile varies greatly over the course of a day, driven primarily by wind.; Chapter 4 focuses on the diel cycle of the soil CO2 profile in the boreal forest of northern Manitoba. As with the marsh soil, the soil CO2 profile shows a pronounced diel cycle caused by wind. The soil CO2 storage flux is compared with the canopy CO2 storage flux and soil CO2 efflux.; In Chapter 5, automated soil CO2 profile measurements are used to study the seasonal pattern of CO2 production in the soil. The contribution of the deep soil to total profile production rises over the course of the summer. The sensitivity of deep soil CO2 production to the temperature at 50cm depth was found to be 0.6 kgC/m/day per degree Celsius.; Chapter 6 presents additional CO2 and 222Rn soil profile data collected in northern Manitoba. The data suggest that deep soil respiration represents a higher proportion of total profile production in forest stands that have burned more recently.; Finally, in Chapter 7, I assess the hypothesis of Goulden et al. [1998] that deep soil decomposition has accelerated dramatically in the northern Canadian boreal forest due to recent climate warming and outline future work needed to improve the automated system.