A System for Studying the Dynamics of Gaseous Emissions in Response to Changes in Soil Matric Potential.

An incubation system was developed to study the dynamics of greenhouse gas emissions from soil cores at different matric potentials. It combines the facility to establish and easily alter matric potential in soil columns, contained in nine parallel incubation chambers, with the feature of highly time resolved measurements of NO, N2O, N2, O2, and CO2. Studies on chamber performance demonstrated that the repeated application of specified suctions or pressures gave highly reproducible water contents and that the water release curves were similar to those obtained with traditional methods. The system was used to examine how soils preincubated at -5 or -75 kPa for 90 d responded to matric potential increases during a subsequent anaerobic incubation. The data showed that as large pores were filled with water rates of both CO2 evolution and total denitrification increased up to -2 kPa. This is in contrast to aerobic studies that show a decline in CO2 evolution at such high matric potentials. The data suggest that C that was not decomposed in large air-filled pores during the aerobic preincubation became colonized only when these pores became water-filled in the subsequent anaerobic incubation and provided substrate for denitrifying organisms. These studies demonstrate the capacity of the incubation system to explore the complex interaction between soil structure and the microbially mediated soil processes responsible for gaseous N and C emissions. This interaction is crucial to understanding factors controlling gaseous emission rates but has historically been difficult to be examined directly. [ABSTRACT FROM AUTHOR]