X‐ray computed tomography to predict soil N2O production via bacterial denitrification and N2O emission in contrasting bioenergy cropping systems

摘要

While renewable biofuels can reduce negative effects of fossil fuel energy consumption, the magnitude of their benefits depends on the magnitude of Nsub2/subO emissions. High variability of Nsub2/subO emissions overpowers efforts to curb uncertainties in estimating Nsub2/subO fluxes from biofuel systems. In this study, we explored (a) Nsub2/subO production via bacterial denitrification and (b) Nsub2/subO emissions from soils under several contrasting bioenergy cropping systems, with specific focus on explaining Nsub2/subO variations by accounting for soil pore characteristics. Intact soil samples were collected after 9?years of implementing five biofuel systems: continuous corn with and without winter cover crop, monoculture switchgrass, poplars, and early‐successional vegetation. After incubation, Nsub2/subO emissions were measured and bacterial denitrification was determined based on the site‐preference method. Soil pore characteristics were quantified using X‐ray computed microtomography. Three bioenergy systems with low plant diversity, that is, corn and switchgrass systems, had low porosities, low organic carbon contents, and large volumes of poorly aerated soil. In these systems, greater volumes of poorly aerated soil were associated with greater bacterial denitrification, which in turn was associated with greater Nsub2/subO emissions ( R sup2/sup?=?0.52, p ?0.05). However, the two systems with high plant diversity, that is, poplars and early‐successional vegetation, over the 9?years of implementation had developed higher porosities and organic carbon contents. In these systems, volumes of poorly aerated soil were positively associated with Nsub2/subO emissions without a concomitant increase in bacterial denitrification. Our results suggest that changes in soil pore architecture generated by long‐term implementation of contrasting bioenergy systems may affect the pathways of Nsub2/subO production, thus, change associations between Nsub2/subO emissions and other soil properties. Plant diversity appears as one of the factors determining which microscale soil characteristics will influence the amounts of Nsub2/subO emitted into the atmosphere and, thus, which can be used as effective empirical predictors.